AmericanLongRifles Forums
General discussion => Black Powder Shooting => Topic started by: Acer Saccharum on May 05, 2009, 04:12:07 PM
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A friend of mine sent me what he's been thinking for his next gun. Frankly,I don't have the experience to know what to tell him, but his idea intrigues me. Keep in mind, this is for target shooting only, which is also my main interest.
Also, I am probably going to take some liberties on the caliber. Since this will be used for target shooting (I have enough hunting muzzleloaders), I'm thinking of a smaller caliber...45 with a faster twist than usual..1-48. This will limit the recoil somewhat and reduce the powder charge. What really impressed me several years ago was a the world championships (I forget where, maybe Germany) where I watched a Swiss competitor shoot a repro perc. Schuetzen rifle offhand at 50 meters. The target is similar to a NMLRA 100 yd. target. He put them all in the 10 ring (13 shots...best 10 count, worst 3 discarded, all his 13 shots were 10's). Now, I know a few NMLRA guys that, on any given day, could do that also. But what was really impressive was that you could not even tell he had fired, except for the muzzle smoke: He didn't move a fraction of an inch. No discernable recoil. I spoke to him later (a little confusing since he didn't know English, so we did it in French of which I was semi-fluent at the time) and found that he had a 45 cal very fast twist (1-24) and he was using a round ball with a 35 grain 3F charge. This may all be gibberish, but I'm going to try a 45 cal., 1-48 twist on the Jaeger.
That said, I'd be interested in what you guys think of this, or your experiences with such a rig.
Acer
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I'll throw in what little I can here..... Safe to assume that he was not actually shooting 35 grains (as we know it i.e. Goex, Schuetzen etc.) but was shooting Swiss which computes as something like 42 grains (as we know it). That 48 twist I'm told is @!*% critical as to charges meaning fussy. They will shoot well but you have to find the exact amount of powder to use and no spilling please. A few grains off = rotten shot! Slower twists being more forgiving.! The Schuetzen style of rifle can be held steady by some folks since the hooked butt plate helps prevent the rifle from slipping around on a shooter's shoulder, and helps hold her steady.
Was the Swiss shooter using a palm rest? And a hip rest (elbow on hip)!?
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I'd have used a 48" twist in my .45, however was after a trail-match + hunting twist, so chose the 60" GM barrel. Yes, it requires a descent charge to shoot well, oh well, it doesn't kick at all, being a .45 of 9 1/2 pounds. It's preferred charges are 75gr. 3F or 85gr. of 2F - some what heavier than the norm for most shooters of .45 cal. rifles. I see no difference in fouling as they both shoot seemingly 'cleanly' in that the bore is wiped by the next ball/patch to the bottom of the grooves and no fouling builds for a day's shooting.
The 48" twist has long been a favourite of bench shooters, but be aware it requires more care, I think in developing an accurate load. Being, that is may want a specific charge and 5gr. above or below that might not shoot well at all.
The .40 cal. barrel I have is a 48" twist and is somewhat particular in it's diet depending on temperature, it seems. In the winter, (sub freezing)it seems to prefer a light oil lubed patch, while in the summer it likes spit - same patch, but with 2f and a lighter charge as well. Winter uses 65gr. 3F while summer uses 55gr. 2F. With 2F, I have to prick the vent each shot as if I don't in 2 to 4 shots, a piece of fouling at the pan will block the vent. It's easier to prick it each shot - HA! - if I don't though, it shows if I'm flinching when it 'foof's on a blocked vent.
I think twist might depend on what your accuracy requirements are, Tom. I've a feeling the 48" might be more accurate than the slower twists - but perhaps a bit more finicky to loading. The larger the bore in a 48" twist, perhaps the more finicky. On the other hand, my .58 has a 48" twist and it shoots well several loads and isn't as finicky to lube as the other two barrels. It does not like heavy charges, though, however will shoot well enough with them for hunting purposes.
The barrel will, of course, will you want it wants or demands. There isn't much difference between 48" and 60", but small differences like these seem to matter.
I think you can find a load that will shoot amazingly well is a very fast twist like they guy with the Scheutzen rifle. But one like that might be a close range rifle only. With lower velocities, higher trajectories. I'd not go faster than 38" .50 cal., which shot for me with round ball only after I choked the barrel.
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The above is all I have at this point, Roger.
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The schuetzen game is different from what most of us are used to. One individual explained to me that you have more time to shoot and take it. Fouling is not likely an issue as the gun is cleaned between shots. Loading is done very carefully. We have had discussions on this in other threads, but a Schutzen rifle is a heavier off hand rifle such that a 45 with a lighter charge would not kick much. My wifes rifle is a 45 with a 1-48 twist and is not a fussy as some suggest. But she did very well with 45 grain charges. I basically set the rifle up for her and found that range 45-50 grains to be about the best. Hers was a flintlock, and a percussion may do a little better with lighter loads. I would be willing to bet taht 35 in a 1-24 inch twist would be accurate. What I am curious about is the conversion factor as Europeans use metric.
DP
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Acer,
I don't have experience on the question directly, but the way I look at the question goes to the issue of gyroscopic stability and what's required to do that with round balls. It's a queer subject in several regards, firstly because round balls don't really require gyroscopic stability since their center of aerodynamic pressure (cp) and center of gravity (cg)are essentially the same. Given that, it follows that slow twists work adequately to meet requirement that the ball simply be spun sufficiently to present its variables in consistent fashion to aerodynamic forces which act upon it. That is the basic difference between smoothbores and rifles. Smoothbores allow small random presentations by the ball to aerodynamic forces thus their dispersion is greater. They shoot "knuckle balls". A twist of 100-120 x ball diameter is sufficient to provide the consistency needed.
A well known shooter in the realm of round ball bench guns named Crowley used a .50 caliber gun twisted at 113" some years back with success. That's a wide variation from the guideline above, actually 226 x caliber...it illustrates what is required vs. what can or might work. Faster twists can work, but they might also be counter productive since they will exacerbate imbalance caused by voids in the ball or other imperfections. And nothing is perfect. I'm guessing the information your friend references says more about the shooter than the twist rate.
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I like the Schuetzen game, and would like to build a flint schuetzen just to bother the competition. It's a bit of an anachronism, to say the least, to put a flint lock on an 1870's gun. or is it a regression?
Many of these matches are 200 yds offhand. fifty shot match, 12" bull, iron sights. heavy guns. You are tired at the end of this match, lemme tell ya.
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Dan, what I think about roundball spin:
1) a smoothbore has no rifling, so the ball may come out of the muzzle with top spin, or side spin, causing the ball to climb or crab sideways, hence the difficulty in getting a tight grouping on the target.
2) rifling merely give the ball a consistent spin, so it's presentation to the atmosphere, once free of the muzzle, is always the same. This rotation is only useful to eliminate the atmospheric effects that the ball suffers in #1. A round ball should not need to be spinning to be stable, in theory.
3) rifling, if fast twist, creates resistance to moving the ball down the barrel, causing higher initial pressure buildup. Too much powder, and the ball may strip in the rifling. So light loads may give the desired spin, yet reduced recoil. I think you'd have a higher trajectory, which could be a negative, unless you had the approriate sights, and knew the settings for each range.
4) rifling, if slow, creates less resistance to getting the ball moving, yet still imparts the rotation which we know and love. Slow twist will allow use of a wider range of powder charges. Disadvantages might be recoil, if excessively loaded.
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I'm guessing the information your friend references says more about the shooter than the twist rate.
Dan, that there is a mouthful!
If the shooter's roundballs were swaged and weighed to eliminate the balls with voids, just that alone would go a long way toward making a gun shoot well.
Tom
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Most serious target shooters, as in bench rest, seem to see a trend in accuracy with round ball as fast twist =lighter charges slow twist =heavier. It gets argued with examples of exceptions but it seems to follow that trend. If the range is known trajectory is not so much of a problem as sights can be adjusted, its the wind that will get you at 100 yards or farther. 1-48 is not unpopular in the rest type accuracy events.
DP
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If the .45, 1 in 48 is popular, what kind of rifling? I would assume square, sharp rifling would be the order of the day.
Muzzle protector(like a false muzzle, but not rifled) would be a good idea, methinks.
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Tom- all the above rings true for me. It would be interesting indeed to shoot a round ball rifle with a false muzzle. Not that difficult to build if one has the requisite machinery and skill & knowledge of what is required. Between Taylor and I, I suppose we could be a 'bang-up' job, so to speak. Time- that's the problem - too many projects - so little time. He's got two on the go now, and a third coming in the mail!
Instead of that Hawken he's talking about, I think he should do the .25 first.
Regarding the smoothbores - those shooting perfectly round balls WITHOUT sprue will range farther than those with a sprue that catches the wind and starts the spinning - into trumpet-shaped patters close-in with light charges, farther out with heavy.
I'd say go ahead with the 48" twist - or even 38" or 32". As to rifling shape, I really like the Goodioen barrel's styling with the double wide (or more) grooves - flat bottomed - and the narrow, very thin lands. They load tight combinations easily & tight shoots the best - for me.
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I had a 1:48 twist rifle in .54 caliber that I shot for a while. Like some others have said, it was fussy about powder charge and the groups opened up either side of the best charge. What was strange was that the most accurate velocity was not the same for 2F and 3F powder. In my case 55 grains of 3F and 85 gr of 2F were the most accurate charges and they had dramatically different velocities.
cheers Doug
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I hear you Doug- my .40(48") shoots the same velocity with 3F or 2F - in the winter, but wants 200fps slower in the summer - go figure. In the .45 (60"), the 3f shoots 100fps faster than 2F - both with the most accurate loads.
Rifles are are different & if worked with, will show their idiosyncrasies.
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Dan, what I think about roundball spin:
1) a smoothbore has no rifling, so the ball may come out of the muzzle with top spin, or side spin, causing the ball to climb or crab sideways, hence the difficulty in getting a tight grouping on the target.
2) rifling merely give the ball a consistent spin, so it's presentation to the atmosphere, once free of the muzzle, is always the same. This rotation is only useful to eliminate the atmospheric effects that the ball suffers in #1. A round ball should not need to be spinning to be stable, in theory.
3) rifling, if fast twist, creates resistance to moving the ball down the barrel, causing higher initial pressure buildup. Too much powder, and the ball may strip in the rifling. So light loads may give the desired spin, yet reduced recoil. I think you'd have a higher trajectory, which could be a negative, unless you had the approriate sights, and knew the settings for each range.
4) rifling, if slow, creates less resistance to getting the ball moving, yet still imparts the rotation which we know and love. Slow twist will allow use of a wider range of powder charges. Disadvantages might be recoil, if excessively loaded.
Acer,
#1, that was what I was trying to get out.
#2, Ditto
#3, I think twist and stripping are a deep discussion in their own right. Related factors that spring to mind are alloy, groove depth, ball/patch/bore dimensions, and pressure. I'm not convinced that quick twists contribute greatly to stripping, particularly with PRBs. On another thread here about load inertia I posted some fair groupage (photo) with a paper patched conical from a cartridge gun. The bullet is 300 grains of pure Pb and launched with about 35KPSI at 1600 fps from a 20" twist. As the velocity moves up to the 1675+ fps range accuracy falls off quickly and right or wrong I attribute this to stripping. The transition is very abrupt, starting around 1675 fps.
On a second point about twists and resistance, I am also undecided. The energy required to impart angular momentum in conical jacketed bullets is very small as a proportion of total expended chemical energy. Less than 1/2%. It is probably less with muzzle loaders due to lethargic twist rates. Fast twist rates will cause more resistance to engraving the bullet from cartridge guns but that is not a factor with muzzle loaders since the bullets are somewhat pre-engraved by loading.
#4, The Crowley fellow I mentioned previously was of a mind that slow powers fared better in fast twists and vice versa. I'm pretty sure he had tongue in cheek in discussion about loads for his .50 with the slow twist, but he did use enormous charges of fffg in that gun. He mentions using a short starter to seat the ball, and I don't know if he was joking or not. He did say after the first shot at a match as Saratoga the range officer made him move out from under the covered line due to offensive concussion. This was published in a March issue of Muzzle Blasts sometime in the 70s, the year not clear...maybe 1974?
Anyway, your thoughts on powder choice versus twist seem congruent with Crowley's thoughts. He considered use of 4f in his bench gun. :o Then there is my picket rifle with the 38" twist that prefers Swiss 1-1/2 Fg. ??? Maybe I should try cannon grade? I dunno.....
Swagged balls are more consistent in my opinion, if all else is equal. They are not perfect though.
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When I started this game back in 1976 I bought a TC renegade with a 26" .54 1-48 twist barrel. I didn't know the barrel was too short or the twist was too fast to shoot well. I just developed a load (took awhile) and started hunting and going to matches. That was the year my son was born and I wasn't but a year or so above 20.
My most accurate loads ranged from 55 to 85 grains 2F. Above that the groups started to open. For 25 and 50 yards 55 got the nod. A lot of time was spent on the bench and the idea that I wasn't properly outfitted for this stuff never occured to me.
I gained quite a reputation locally. One year at the Southeastern regionals I placed 3rd in 50 yard offhand and also took a 3rd in one of the 25 yard matches. I never attributed my not winning 1st with haveing a barrel too short or rifling too fast. I just thought I needed more practice and experience.
Of course now I'm older and wiser and I know better. I still have the renegade but it's relagated to the back of a closet. I wouldn't dare take that shortbarreled, fast twist, inaccurate and highly inappropriate rifle to a match again. Never!
My groups have opened up a lot but I know its not those longbarreled flintlocks, it has to be my age.
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There is a difference between target guns and guns/rifles used for other purposes.
If you were shooting over a stockcade or out a loop hole at antagonists 150-300 yards away the 35 grain load would be a limited usefulness. It would be a poor choice for a hunting rifle for the same reasons.
It has been proven that fast twists and a rb will shoot very well with light powder charges this from the flintlock era. But it does so at the expense of velocity and the ability to hit anything past 50-60 yards unless the range is known exactly..
IMO an American rifle before 1800-1830 with a twist much under 48" would be an anomoly.
Concerning the 48" twist. This twist got a blackeye with the T/C Hawken with a 48" twist and shallow rifling. In reality it is OK to ball sizes to at least 50-54 with about 1/2 ball weight of powder if the rifling is .010-.012 deep. It might even be preferable with 50 cal.
Dan
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Hi- I'm the guy that started all this talk about round ball fast twist barrels. Acer Saccharum posted it on this site based on an e-mail I sent him. I am very impressed with the info you all have posted. My goal is to make a pre-Rev War Jaeger to be used in BAR (Brigade of the American Revolution) shoots. It has to be historically accurate. Events are mostly at 50 yards, a few at 25 and some at 75. I'll just be punching paper and blasting a few breakables. Nothing out to 100 yards or more.
I was thinking about the faster twist of 1-48 to reduce recoil (supposedly will use a lower powder charge). The barrel length would be around 38". 45 caliber is kind of small for a Jaeger, but again, I'm looking for a light powder charge. My reference to the Swiss Shuetzen shooter was only to make reference to someone that is already doing this successfully.
Thanks for all the input...especially about how finicky the proper powder charge may be. I'm still a long way from building this gun..just started getting my thoughts together. You have all been a great help.
Rick
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You are overly concerned about recoil, which is negligible for target loads in a properly fitting gun. I shoot a .50 cal with a 1/66 twist. My loads are as follow:
25 yards.........30 gr
50 yards..........50 gr
100 yards........70 gr
With these loadings, point of impact is the same using 3F Goex. None of them produce any noticeable recoil.
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You are overly concerned about recoil, which is negligible for target loads in a properly fitting gun. I shoot a .50 cal with a 1/66 twist. My loads are as follow:
25 yards.........30 gr
50 yards..........50 gr
100 yards........70 gr
With these loadings, point of impact is the same using 3F Goex. None of them produce any noticeable recoil.
Exactly right!!! What recoil ???We shoot these rifles in thin shirts no problemo and I'm pretty skinny! Actually underfed and underloved ::) ;D ;D
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Actually ... underloved ::) ;D ;D
Roger, we all love you.
Welcome, Rick!
Hahahaha. I knew if I told you about the ALR, it wouldn't be long before you were hooked. Glad to see you sign up. (Rick goes to Dixon's frequently, and will be going to the Fair.)
Tom
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You guys are right. I've been over thinking this. I have been shooting flint rifles with twists from 1-60 to 1-72 since the late 60's. I think I'll stick to the slower twists that I know how to work up a load for and that are probably more forgiving.
Now, I have an original target rifle from about 1870 that is 42 cal. with a twist of 1-42 that's giving me a problem....never mind...one thing at a time. :D
Rick
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I've found most accuracy problems, given a good bore & enough powder, can be eliminated or severely reduced with a heavier patch. I was amazed how much powder I had to use in my .40 with 48" twist. I would expect a .42 with 42" twist to like something in the 50 to 55gr. arena.
In small bores - less than .69 I use the same powder charge at all ranges - whether we're shooting playing cards on edge at 10 yards or foxes and rabbits at 100 yards.
As to a very accurate rifle of the Jaeger persuasion, I'd think a .58 or .60, with a 48" twist and shooting 60gr. to 70gr. of powder might give the best accuracy. The larger balls are forgiving and the faster twist shoots well with those small charges. I know this due to the 24" barreled Musketoon- an exceptionally accurate rifle with round balls, considering the rifling style is for slugs, not round balls. The gun doesn't seem to know it shouldn't shoot RB's well. I've only benched it to 40 yards so far, and bug-holes are the results for 5 shot groups with these light charges. Recoil is neglegible.
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What are we talking here? National championship shooting? How well did the second place finisher do?
When we're talking a score of 130 (the 3 scrubs were also 10s) little tiny differences can matter.
One thing that comes to mind is the pressure when the ball leaves the muzzle. I would imagine that less pressure behind the ball the moment it leaves the muzzle would be better. This can only be accomplished with small charges in a long tube. And to get a stabilizing spin with a small charge one needs a fast twist.
Personally, my shooting will never get to the point where I would notice such fine details. It's like really fine wine - it's just waisted on my taste buds. Thus if I shot the same gun that won the world championship, it probably wouldn't improve my score over shooting my regular gun.
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I hear you Doug- my .40(48") shoots the same velocity with 3F or 2F - in the winter, but wants 200fps slower in the summer - go figure. In the .45 (60"), the 3f shoots 100fps faster than 2F - both with the most accurate loads.
I chronographed one of my 54s comparing 2F, 3F, and some non commercial Swiss powder using 50 grains of each as I recall. The 3F was 100 fps faster than the 2F and the Swiss was 100 fps faster than the 3. The Swiss that I used was heavily graphited and finer than 3F powder and I would be reluctant to use a heavy charge of it because it definitely gave quite a crack compared to any charge of Goex I have ever used.
Also worth noting that when I used to shoot the fast twist 54, in really damp weather, I would often up my charge by 5 grains because I kept powder in a horn and felt that it probably absorbed a small amount of moisture.
I also had a short barreled jaeger (barrel was probably shortened) with a twist of 1:26 and caliber .63 that shot well enough for rondyvous with roughly 60 gr of 3F. I never tried more because being an old gun I was reluctant to stress it. Never tried less because my first choice of 60 gr worked well enough :>)
cheers Doug
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The relevance of twist rates to round ball stability notwithstanding, increasing velocity is a poor way to seek stability in any bullet, be it a round ball or conical. I'd say the matter of spin stabilized projectiles is fairly complex for many reasons not worth putting forth here...let it be known that upping the velocity has little merit if the objective is to influence gyroscopic stability. In part the reason is the influence of drag and overturning moments increases substantially in the transonic range and peaks at Mach 1.
Light target loads that do not stabilize a bullet at...oh....say 900 fps, will certainly not do so at 1160 fps or there abouts.
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The relevance of twist rates to round ball stability notwithstanding, increasing velocity is a poor way to seek stability in any bullet, be it a round ball or conical. I'd say the matter of spin stabilized projectiles is fairly complex for many reasons not worth putting forth here...let it be known that upping the velocity has little merit if the objective is to influence gyroscopic stability. In part the reason is the influence of drag and overturning moments increases substantially in the transonic range and peaks at Mach 1.
Light target loads that do not stabilize a bullet at...oh....say 900 fps, will certainly not do so at 1160 fps or there abouts.
This a whole "nother" can of worms.
Such as why to smoothbores often shoot best with heavy loads?
Why will some rifles not shoot light loads at all.
I have a 54 Douglas that is useless a 25-30 yards with 50-60 grains of FFFG.
So I shoot the HV load at everything.
I had a 72 twist 54 that was pretty harmless with 100 and did not tighten up till 120.
Now we can ask if this was some idiosyncrasy of the barrel or was it something to do with rotational speed.
Lots of people hear report heavy loads shooting better than the light ones. Like 60-70 gr in a 40 cal.
Then we have picket bullet guns in which the picket often requires more powder than the RB. The best load so far in my 40 cal with a 132 gr picket is 80 gr of FFG Swiss. I would have to go grab one but its about .7" long.
May not be the increased rotational velocity but something is going on.
Dan
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My 54 starts shooting for close range with about 70 grains of 3f which is not a heavy load. At 25 and 50 yards 70 grains does all that I need it too. I had a 58 Numrich whcih I think had a 72 twist. It shot very well with 70grains and then jumped up to 110 of 3f to shoot well. Most of the guns I went through followed a general pattern. I do think the 40 I had, with a 1-48, needed a heavier charge as Daryl suggested as I never quite liked the lighter charges. But then if you need to shoot heavy charges in a 40 why not shoot the same thing in a 45 and get better wind advantages? Thats why I am not real fond of small bores as they seem to need too much to get them to shoot. The 25 I am building should be small enough not to matter. The 45s 50s and 54s seem to behave the way they should. Go bigger and you have great hunting guns but they will thump the heck out of you for target matches. I have felt for some time that twists are made too slow and faster twists could give some advantages. The schutzen cartridge principle, use a smaller case and a heavier bullet for best accuracy as exemplified by the 38-55. Why not in a large bore ML. Say a 58 with a 1-48.
DP
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The relevance of twist rates to round ball stability notwithstanding, increasing velocity is a poor way to seek stability in any bullet, be it a round ball or conical. I'd say the matter of spin stabilized projectiles is fairly complex for many reasons not worth putting forth here...let it be known that upping the velocity has little merit if the objective is to influence gyroscopic stability. In part the reason is the influence of drag and overturning moments increases substantially in the transonic range and peaks at Mach 1.
Light target loads that do not stabilize a bullet at...oh....say 900 fps, will certainly not do so at 1160 fps or there abouts.
This a whole "nother" can of worms.
Such as why to smoothbores often shoot best with heavy loads?
Why will some rifles not shoot light loads at all.
I have a 54 Douglas that is useless a 25-30 yards with 50-60 grains of FFFG.
So I shoot the HV load at everything.
I had a 72 twist 54 that was pretty harmless with 100 and did not tighten up till 120.
Now we can ask if this was some idiosyncrasy of the barrel or was it something to do with rotational speed.
Lots of people hear report heavy loads shooting better than the light ones. Like 60-70 gr in a 40 cal.
Then we have picket bullet guns in which the picket often requires more powder than the RB. The best load so far in my 40 cal with a 132 gr picket is 80 gr of FFG Swiss. I would have to go grab one but its about .7" long.
May not be the increased rotational velocity but something is going on.
Dan
It is indeed....another can of worms. Fortunately there be some well defined principles of physics which takes the necessity of in depth twist rate analysis out of the equation for round balls, so we can look to other causes as we speculate on the subject. ;D Round balls need a little spin...they either have it or don't; case closed.
The "O" word comes to mind, but that is speculation.............
Round balls and exterior ballistics are as simple as the combination gets, whether it be smooth bores or rifles. I would ask you all to accept that, if for no other reason than you really don't want to read an in depth explanation about gyroscopic stability and so forth. I don't want to get into it anyway, because it really isn't pertinent to PRBs beyond what I've already stated. I will be happy to provide references to the subject if you want, but in the end all you'll be left with is a headache and the same understanding I have. When you get into conicals it becomes a very complex study. Just another reason to stay away from those bullets longer than they are wide. ;D
In simple terms:
1) 1:60" twist @ 1000 fps = 200 revolutions/second (rps) or 12,000 rpm
2) 1:48" twist @ 1000 fps = 250 rps (+25% of #1)
3) 1:36" twist @ 1000 fps = 333.3 rps (+33.3% of #2, or +66.7% of #1)
4) 1:60" twist @ 1250 fps = 250 rps
By the by, a child's top stabilizes as a much slower spin rate than 12,000 rpm. So do round balls, just for very different reasons. One does not need to over think this....
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Dan
I guess you could try spinning the kids top in a supersonic wind tunnel to see if the "relative wind" effected its stability.
Why is it that 72 twists are known for needing more powder in 50-54 cal than a 48 or a 66 to shoot with best accuracy? Its not that they can use it without stripping, they seem to NEED it in many cases.
It seems from my reading and experience that a significant number of rifles like quite a bit of powder.
I have read reports of 40 cal RB rifles shooting best with 60-70 grains of powder. Is it a requirement of the individual barrels, how they are keyed to the stock, internal stress or is it initial rotational velocity?
Look at the heavy benchrest RB shooters. Why do many of them use so much powder? Why are they doing this?
How about velocity bleed off? Most RBs are subsonic at 100 yards regardless of initial velocity.
But does the higher initial velocity, giving a higher rotational velocity, (which falls off far more slowly than the linear velocity) make the RBs more stable as they pass through the high drag transonic range?
Is this why faster twists shoot better, usually, with smaller powder charges than slow twists?? Is it the initial rational velocity keeping them more stable at the high drag velocities?
Is this why some bench rest shooters use large charges of powder to shoot 150-200 yards with a PRB?
How does ball size effect the need for more or less twist?
Forsythe tells us that a 69 cal. (14 bore) can use a 8' 8" twist and will shoot at well as he can to 200-250 yards. But that a 12 twist will only shoot to 150 with the same accuracy. Why is this? If the twist is irrelevant so long as it has "some" then the 12 ft twist should shoot as well as a 8'8" to 200-250 yards. Is Forsythe just pulling our legs?
There has not been much interest in the scientific community, such as gov't ballistics labs, in studies of spin stabilized RB ballisitics that I know of. In fact, at least until a few years ago, many of these folks did not think a 50-100 Sharps would shoot 1500 yards. So the round ball as a rifle bullet is somewhat unknown aside from Lyman's book which, my copy at least, does not delve into accuracy of the loads at all.
Dan
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I talked with Ernie Stallman from Badger barrels some years ago about long range BP cartridge shooting.
He said they developed loads and spins to keep the bullet BELOW the speed of sound, 1200 ft/sec.
The bullet breaking the sound barrier would disturb the accurate flight.
I don't know if this has any effect on patched roundballs, but some of it might translate. If you are above the speed of sound upon leaving the muzzle, you might want to have it stay above the speed of sound until the bullet is done. ie, passed thru it's target at the intended range.
Just thinkin out loud.
T
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I talked with Ernie Stallman from Badger barrels some years ago about long range BP cartridge shooting.
He said they developed loads and spins to keep the bullet BELOW the speed of sound, 1200 ft/sec.
The bullet breaking the sound barrier would disturb the accurate flight.
I don't know if this has any effect on patched roundballs, but some of it might translate. If you are above the speed of sound upon leaving the muzzle, you might want to have it stay above the speed of sound until the bullet is done. ie, passed thru it's target at the intended range.
Just thinkin out loud.
T
This depends on how far you are shooting. In BPCR silhouette the velocity is not so important. And the reduced velocity can actually reduce wind drift. But the flatter trajectory is an aid as well and my best silhouette rifle shot a 380 gr at 1425. Using too much elevation tends to move the shooters face off the stock. Trade off..
The launch angle of a low velocity load, 1100 fps vs 1350+ can be a factor at 1000 yards.
But there are numerous schools of thought on this too. All have valid points. The old time LR shooters shot 100-105 grains of powder in a 44-45 caliber with 520-550 gr or heavier PP bullet.
I am not sure everything would translate to the PRB but there are some interesting questions. Like does the balls rotational centerline travel at an angle to the "relative wind" at longer ranges as the bullets do.
Few RBs will stay supersonic past 90-100 yards but they will shoot with hunting accuracy to 200 or so, at least the 54s and above.. I think having sufficient rotational velocity at the trans-sonic velocities in important and this can be achieved by velocity better than by a fast twist at low velocity. Since the fast twist low velocity greatly raises the trajectory.
Dan
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I am not sure everything would translate to the PRB but there are some interesting questions.
Because of its unique shape, a round ball's ballistic coefficient does not change during its flight. A long bullet does. This change determines the bullet's stability and accurate bullets need to be designed for the range at which they will be shot. A certain bullet may not stabilize for a hundred or more yards and beyond a certain distance it will start to tumble. Each distance will require a different length bullet.
To make a round ball shoot at longer distances one need only to slow the twist down and add more powder.
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Dan, if there's not a booby trap somewhere in all those questions I'm Chinese! ;D ;D
There is an old saying about ballistics: "If all else is equal." Simple concept, but very difficult to put to practical use. More of a conceptual presentation than anything else actually and it says simply that if things are not the same your derived data is subject to question. EX: Same gun, different barrel...not the same. I'm sure you understand that variables are bountiful in this discussion. With the addition of each variable, the conclusions become less valid for broad application. The many comments made to this point about the necessity of heavy charges versus light charges needed to make a gun shoot is but one example.
To the issue of research on PRB ballistics. No, there isn't much out there and there probably won't be until the likes of Mr. Pletcher or like minded types set to and do it themselves. Ballistic research is geared in very much the opposite direction these days. The technology exists but the motive is absent.
Going back in time to Forsythe's day there is nothing but the highest regard for his work and that of others in the field. He was not pulling our legs and in fact it amazes me that the pragmatic approach to ballistic research and their intuition revealed so much to them. And there is the IQ thing at work. Forsythe was fairly brilliant in my opinion. I think his observation about 8-1/2' versus 12' twists are consistent. There is a practical minimum twist rate for a given caliber PRB. I don't know what it is but would think it caliber influenced to some degree. See my comment below about squares and cubes. On the other hand and this goes to the issue of variables, recall the success had by Mr. Crowley with his slow twist rate .50 caliber. Somewhere between the measures Forsythe commented on if I did my math correctly.
I would say that in very general terms, the exterior ballistics of PRB and conical bullets share but a few things. Gravity and drag are the big ones I'd say. Even though both are stabilized by rotation from rifled bores, there are distinctly different reasons for doing so and I think I touched on the primary issue early in this thread.
On the part of conical bullets, the CG and CP are not co-located and as a result gyroscopic stability is required to stabilize the bullet. CG and CP are co-located in round balls, thus there is no prevailing influence of overturning or pitching moments to influence its stability. Like conicals, PRBs are influenced by the magnus force to the extent that balls with random rotation typical of a smooth bore musket will disperse randomly. The slow spin of a RB rifle presents to consistent rotation on a single axis and does away with this adverse factor.
Conical bullets are affected by transition through the speed of sound when the CP shifts and a nutation or wobble is induced as it tries to stabilize from the influence of this upset. From my understanding of the circumstances, not all bullets experience this but in broad terms the CP shift is forward, or destabilizing. Since round balls do not have dislocated CG/CP, I have no reason to think this influences their flight path. I've certainly never seen such representation made in writing. Many folks seem to think the transition through the speed of sound is turbulent. It isn't. Regardless of twist rate or velocity from a PRB rifle, the spin rate is very low. I doubt it has anything to do with stability in the transonic range, either positive or negative. I say this simply because the reasons for spinning a round ball are different than for a conical and PRBs do not carry the same baggage in an aerodynamic sense. Gyroscopic stability in conical bullets presents a lot of penalties for the benefits gained...it is not a free lunch. If you peruse the Nennstiel web site linked below you'll begin to see that if you don't already.
Comment made about the ball orienting itself to the flight path: I don't think it would and such absence would, to very small degree, increase the influence of the magnus force. Understand that the magnus force is very small and not worthy of deep consideration in this discussion. It is present however.
http://www.nennstiel-ruprecht.de/bullfly/magnusf.htm#header
To the question, the act of a bullet's spin axis conforming to the flight path is known as the tractability condition. It occurs because the bullet is 1) gyroscopically stabilized and 2) is pitched up relative to the flow field. This results in nutations of small order and if properly stabilized the bullet will precess to a new pitch axis which reduces the upsetting forces. Again, round balls have co-located CG/CP and there is no upsetting force which might cause the precession. Even if the ball is slightly oblate in shape due to obturation, there is no significant displacement of CP to promote the tractability condition.
http://www.nennstiel-ruprecht.de/bullfly/tractf.htm#header
Random thoughts on variables which may have influence on the observations made by many of you.
1) Obturation is a variable influenced by charge, alloy and probably another half dozen things to small degree. A ball increases cross sectional area by the radius squared as caliber increases. It increases mass by the radius cubed. Raise the caliber, and you raise the BC, SD and a few other things.
2) Different rifles, each with a family tree of variables. Barrel pinning, breech, caliber, lock, patch...it's a long list I think. Each is its own animal.
I dunno that covered all the questions, but it's margarita time. ;)
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From a short barrel, fast twist, this thread took some turns. Certianly not pointing fingers as I'm the worse thread-drifter here. ;D
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It seems to me that the 1:48" twist is the ideal round ball twist for the .40cal...and IMO the .45cal is not all that much different than a .40 so it should follow that the .45 would do well with a 1:48".
I've owned / used multiple T/C standard .45cal x 1:48" barrels over the years, all with max loads and never had anything but great accuracy out of them...same thing in T/Cs .50/.54cal x 1:48" barrels.
I always used snug PRB combinations requiring a short starter and never had any strange fliers or indications that rifling was stripped.
My typical hunting loads:
90grns Goex 3F'
Oxyoke OP wad
.018" pillow ticking
Hornady .440/.490/.530 balls
Typical 100 yard benched groups ranged from 1+7/8" to 2+3/4", iron sights and tired eyes...personally, unless someone is heavy into competition I think 1:48" twists are fine for .45/.50/.54cals
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I like 48" in 50 cal and would not worry about one in a 54.
But there are a host of variables.
How tight is the fit, what is the land groove ratio, what is the groove depth.
I had a 48" twist 50 cal douglas that was probably the best shooting RB rifle I ever owned with 1/2 ball weight of powder.
As I tried to point out in my question post there are a host of variables.
The Europeans who developed the short barrel 1 turn in a barrel length idea were right. It shoots great from all accounts. BUT ITS NOT A HUNTING RIFLE past 30-50 yards.
The slower twist will shoot as well and will provide a flat trajectory or in the case of Forsythe a flat trajectory and enough drive to penetrate large game.
While 5 drams of powder in a slow twist 14 ga barrel 26" long would drive an hard ball through an Indian Elephants head a charge of 50-60 grains as was often used in the fast twist rifles would not.
If you could HIT a deer at unknown ranges with it it would kill. But its still a PITA to use and would be limited to short ranges due to trajectory concerns..
Dan
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From a short barrel, fast twist, this thread took some turns. Certianly not pointing fingers as I'm the worse thread-drifter here. ;D
Well, I'm a frequent offender too. ;D I thought myself well behaved on this discussion though. My bottom line for PRB guns remains enjoyment. They are fun and I enjoy the simplicity. I save all my anal retentive behavior for the other side of the fence with white powder and conicals...mostly.
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I prefer a 1/66 teist on a 45 it is much less forgiving as to what it likes to eat