AmericanLongRifles Forums
General discussion => Gun Building => Topic started by: David R. Pennington on August 29, 2013, 05:55:19 PM
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I was wondering if there is a relation to barrel length and breech pressures in long guns? Anyone discussed that before? Do longer barrels typically need higher or lower charges? So far I've only shot 42-44" barrels but have a 48" barrel .45 waiting on my next project.
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I'm of the opinion that the same charge in a 48" barrel will produce slightly faster velocities than in a 42" barrel. Dagner has a program dealing with such things & may chime in.
Paul
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With a longer barrel do you have issues of the ball residing in the barrel longer? Like if I were to flinch, would I tend to throw the ball worse with a long barrel than a short one?
But I don't flinch, really. :D
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Yes, a longer duration of the ball in the barrel, but, at 1800 FPS, it takes a ball about .023 of a second to travel down the length and out of a 42" long barrel. And with a 48" long barrel, it takes about .026 of a second to exit the barrel,,,, so about .003 of a second difference.
I say 'about' because I'm using a constant velocity, and not factoring in powder ignition, ball acceleration, etc. But none the less, to make a difference in ball impact between the two barrel lengths, you're gonna need to be quick! ;D
John
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I would think that the BREECH pressure would be the same irregardless of normal rifle bbl length. After ignition, there's a "spike pressure" caused by projectile inertia and then a steady decrease in pressure as the projectile proceeds down the bbl.
There's a bbl length that allows complete ignition to occur producing maximum velocity, but that length is load specific......Fred
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In other words, if the load is too light, the pressure will stop increasing while the ball is in the barrel?
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Longer barrels will result in higher velocities than shorter ones Barrel length has no effect on breech pressure unless the barrel is so short that the bullet exits before peak pressure can be attained. In this case, you will blow a lot of unburned powder out of the muzzle.
Here is a graph from a software program I sell. It depicts the pressure velocity curves as the bullet moves down the barrel from left to right.
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi1207.photobucket.com%2Falbums%2Fbb471%2Feddillon%2FALR_zps5f5a652b.jpg&hash=3eff6267815d0e608315d698ad060ae64a1397fd) (http://s1207.photobucket.com/user/eddillon/media/ALR_zps5f5a652b.jpg.html)
RED line is the pressure curve. Blue line is the velocity curve.
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The above velocity and pressure curves would also be applicable to BP but the pressure would be considerably lower. The pressure "spike" overcoming projectile inertia is well illustrated along w/ the increasing velocity and decreasing pressure curves as the projectile proceeds down the bbl. .....Fred
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Very interesting. So in theory, I could expect to get a little more velocity which could result in a little straighter trajectory with no real change in breech pressure?
I remember reading somewhere (can't remember where) the reason the border scouts and pioneers liked a longer barrel was that it was quieter, or to say the report of the gun didn't carry as far a distance as the sound of a shorter barrel. This would be important if you didn't want to attract an enemy's attention or disturb the game in an area?
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I don't have any black powder data to confirm or dispute the longer is faster claim. However, there have been extensive studies of the lowly 22 long rifle cartridge. Maximum velocity is achieved at approximately 16 inches from the breech. The friction factor reduces the velocity beyond 16 inches.
I suspect a modest charge of black powder would behave in a similar fashion.
The studies done with rimfire actually chronographed shots fired as the barrel was shortened incrementally. Any body got a barrel they want to sacrifice to reproduce the tests in black powder?
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It would depend on the powder load. Once maximum burn of the given powder load is achieved, pressure will decrease and the velocity would slow if the ball is still in the barrel at that time, due to lack of more pressure and friction. Think 5 gr vs 100 in a .54. The ball may not even leave the bore with 5gr. The pressure will wain at a given point, if the charge burns out before the ball has exited. Another way to look at it is from a fire hose angle. A 2 1/2" fire hose loses 10 lbs of pressure in every 50' due to friction loss. To get 100 lbs of pressure at the nozzle in 150' of hose, the pump has to produce 130 lbs at the outlet.
Don, you entered as I typed. A very good example. With an equal load in two barrels of different lengths, the longer barrel will produce less velocity.
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This has been done Don, and I've read it.....just can't remember right now. >:(
Was it the back of the one of the old Dixie catalogs???.....I'll dig around, if somebody doesn't beat me to it.
Enjoy, J.D.
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Trying to compare a 22 RF to a BP load is a mistake. Most 22 RF ammo is loaded with a pretty fast smokeless and the pressure drops rapidly past probably 12-14". With standard velocity loads a 26" barrel has a very low report due to sub-sonic MV and the pressure dropping very low at the muzzle.
Black powder is a different propellant.
It has characteristics of a fast smokeless and characteristics of a slow rifle type smokeless, from pressure data I have seen for BPCR. It will impart very rapid acceleration to a bullet but will continue to push it along in longer barrels.
But round balls are not bullets. I suspect that for MOST applications with Modern BP that barrels over 34-36" are of little benefit. But remember the Kentucky rifle prior to probably 1800-1810 did not have access to a modern BP. Powders such as Swiss, Schuetzen and Goex did not exist or at best were very rare in 1800. Swiss for example is much like the highly refined powders of the late 19th C. The technology was not really in place to even make this powder in the 18th C.
So when we look at the long barrels we have to look at them in the context of the powders that were available.
The shorter barreled guns with heavier barrel contours of the last 2/3s of the 19th C are, in my opinion, a rusult of the improvements in powder making starting in the late 18th and early 19th C.
If someone wants to test this they need to order a 48 or 50" rifled barrel blank, straight round is best, screw it on a Pete Allen action and start shooting it with a charge that produces a velocity in 1750-1800 fps range with each of various brands and granulations of powders. Then start cutting it back in increments. But this is going to take a lot of powder an lead if testing say Swiss, one of the other European powders, Goex and their premium powder and one of the cheap import "battle" powders is the barrel is cut back to perhaps 10-12" in 1" or 2" increments with a full range of testing at each length. No need to worry about a stock with the Allen action. The round barrel can be clamped in a set of v blocks. But a good quality chrono needs to be used and it needs to be 15 feet out to reduce damage from patches striking it.
If someone has the energy they could dig out a first edition of Lymans BP book and compare the velocity vs charge vs barrel length between the C&H they used and the GOI. The C&H, being closer to blasting powder than Swiss for example, was pretty poor stuff and took a LOT of powder to make much velocity.
Dan
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Bullets are not propelled by burning powder; they are propelled by expanding gasses which are the result of the burning powder. I think the example cited about the .22LR was with standard velocity ammo. Since the .22LR has very little powder the pressure curve falls of pretty rapidly, but any load with more than a pinch of powder would take a much longer barrel (probably measured in feet, not inches) to see the same result.
Periodically some gunwriter will take a rifle, a hacksaw and a chronograph and prove that shorter barrels produce less velocity with normal loads, and just as often another writer will test ammo in two identical guns and have the shorter barrel produce a higher velocity. What is really proven is that there is no such thing as identical barrels.
The table in the Dixie catalog pretty much shows that longer barells and/or more powder = higher velocity. There are a couple of spots in the table that the data are so close as to be statistically insignificant, however I don't know if it really matters anyway. You are going to build the rifle and work up a load that shoots well, regardless of the pressure or velocity. The increased sight radius of a longer barrel more than offsets any ballistic concerns.
Sometimes I think we know too much and let it get in the way of things that really are important, like hitting where we aim. Natty Bumpo didn't know any of this stuff, and he can outshoot all of us; any day, any time.
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If all the powder has been totally consumed in whatever length of bbl achieved this condition, then each addt'l inch of of bbl length would provide only friction which would decrease velocity. Once the pressure decreases, there's no addt'l force exerted on the projectile and then bbl friction would decrease velocity.....Fred
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I don't have any black powder data to confirm or dispute the longer is faster claim. However, there have been extensive studies of the lowly 22 long rifle cartridge. Maximum velocity is achieved at approximately 16 inches from the breech. The friction factor reduces the velocity beyond 16 inches.
I suspect a modest charge of black powder would behave in a similar fashion.
The studies done with rimfire actually chronographed shots fired as the barrel was shortened incrementally. Any body got a barrel they want to sacrifice to reproduce the tests in black powder?
The boys at Rice Barrels sacrificed a barrel testing velocities.
heres the link
http://www.ricebarrels.com/velocity%20test.html
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I see no benefit in comparing Black powder to smokeless. They are truly apples and oranges. It is my understanding that the internal ballistics of the two are completely different.
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As far as truely long barrels, I've made or owned 5 barrels that were in exess of 60". Two were 45 cal & 3 were 50 cal. Making them shoot accurately didn't seem to be all that different as far as load, from say a barrel of 48" The 50s used around a 100 grs of 2F which is about what we're running in the rest of the 50s. I planed an 83"er one time but never got to shoot it. My gut feeling is that flex should have been an issue. If a barrel could have been long enough for the pressure to decrease & actually loose velocity this one was a good candidate.
Paul
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Don't encourage him. :D. My limited understanding is that all this is also dependent on barrel bore diameter. Even if one could make the same weight ball in 36 and .62, there's sure curves would be different in the same length barrel because of the volume into which the gasses can expand before the ball exits the muzzle.
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Here is a comparison. The only difference is barrel length. 100 gr GOEX FFG. .54 lead round ball. Barrel lenth #1 24". barrel length #2 36". Note velocity difference.
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi1207.photobucket.com%2Falbums%2Fbb471%2Feddillon%2FBP_zps348952e4.jpg&hash=5fdd3afeababead5c4eea77b88b927287349123e) (http://s1207.photobucket.com/user/eddillon/media/BP_zps348952e4.jpg.html)
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi1207.photobucket.com%2Falbums%2Fbb471%2Feddillon%2FBP36_zps3eb5adfc.jpg&hash=ae7d8376ced4f6561a53a9c4ffe8f93461bb23f3) (http://s1207.photobucket.com/user/eddillon/media/BP36_zps3eb5adfc.jpg.html)
There is a limit to lengthening the barrel. There is a point where the friction and the pressure that moved the bullet are equal to the air pressure in front of the bullet. At that point the bullet comes to a halt.
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There is a limit to lengthening the barrel. There is a point where the friction and the pressure that moved the bullet are equal to the air pressure in front of the bullet. At that point the bullet comes to a halt.
Golly, there are comedians everywhere.
But you bring up a good point, Ed. Of course you'd not make a barrel as long as you jokingly suggest. Suppose you want to get maximum velocity for your powder. But you also want a barrel that is a practical length to load/clean and carry.
In the chart below, which I understand is for smokeless, I'd say there isn't a lot of gain past 10 or 15 inches. But what is the 'Point of little gain' for a muzzleloading barrel? And it seems like that point would be load-specific.
(https://americanlongrifles.org/forum/proxy.php?request=http%3A%2F%2Fi1207.photobucket.com%2Falbums%2Fbb471%2Feddillon%2FALR_zps5f5a652b.jpg&hash=3eff6267815d0e608315d698ad060ae64a1397fd) (http://s1207.photobucket.com/user/eddillon/media/ALR_zps5f5a652b.jpg.html)
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Can you stretch the barrel lengths out on your estimator?
The original question was the difference in velocity between barrels 42-44" and one 48" long.
With a 24" and a 30" barrel, of course you'll have an increase in velocity. The Rice barrel test showed that velocity was faster at 42", than in a barrel shorter than that. Question is, is it still increasing at around 48" barrel length, or has pressure peaked and friction has started to slow it down?
John
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John, it's my understanding that you can keep increasing the pressure, as long as you have the fuel to burn.
So if you have a longer barrel, yes you can get the ball to travel faster from a 48" than from a 32", as long as you have more powder.
But there are practical limits to what your shoulder can take, and are your arms long enough to load the rifle.
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Can you stretch the barrel lengths out on your estimator?
The original question was the difference in velocity between barrels 42-44" and one 48" long.
With a 24" and a 30" barrel, of course you'll have an increase in velocity. The Rice barrel test showed that velocity was faster at 42", than in a barrel shorter than that. Question is, is it still increasing at around 48" barrel length, or has pressure peaked and friction has started to slow it down?
John
one thing interesting in the test conducted by Rice was that there was a decrease in velocity every time the barrel was shortened EXCEPT the 34 inch velocities were faster than the 36 inch velocity.
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Seems to me , there was a chart in a Dixie Gun Works catalog some while back that shows the velocity for a given charge in a .40 cal barrel that they cut shorter in increments. Interesting. The velocity did diminish as the barrel became shorter, however the differences /variances increased as the length decreased. That is, there was more of a difference between 20 and 30 in barrel, than 30 and 40 in. If I recall correctly, the difference between 20 in or so and 40 or 42 in was in excess of 200 fps
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So if you have a longer barrel, yes you can get the ball to travel faster from a 48" than from a 32", as long as you have more powder.
I would tend to agree with this. Also the granulation of powder comes into play. We used Goex 1F in the longer barrels & achieved good results. Being slower burning it would tend to still be active further from the breech. But as far as what length a barrel starts going the wrong way as far as velocity with reasonable loads, velocity is still on the increase at 48" & I've seen no sign of decrease at 60"
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Rather than the length of barrel [ reasonable length ] it is the powder charge that will reach a limit for the bore size where you will begin to see a decreasing increase in velocity per charge increment, and then a decrease in velocity. The larger the bore size, the more powder you can use before this occurs. I'm certain that I've seen evidence of this somewhere, but can't find it at the moment.
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If your charge is so big that the ball is halfway down the barrel when sitting on the powder, then you've effectively reduced your barrel length. :D
It's kind of a joke, but there's some truth in it.
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As a couple of us attempted to point out trying to use smokeless as a comparison is not going to work. Especially 22 rf which it is well known will start to suffer velocity loss in barrels over about 18" (depending on the loading used).
While BP is velocity limited it will continue to increase velocity with quite long barrels because it does not work like smokeless does. For that matter many of the Palma Match rifles have long barrels (for moderns) because it allows them to maximize velocity on the cartridges used which are marginal at 1000 yards. So modern CFs like 308 win can achieve a velocity benefit from a 30" barrel though most sporting rifles in this caliber are 22".
Smokeless powders can be engineered for specific applications. Short barrels, long barrels, straight cases or BN. Little or no smoke (relatively) reduced muzzle flash with the same ballistics.
I would also point out that 150 fps variation in a BP arm is a far different thing that the same variation in a smokeless powder firearm making much higher velocity.
If one loads his 45-70 with a lot of powder the produces 1300 fps and then gets a lot that only makes 1150 with the same charge weight there will be significant problems especially if the cartridges are not marked as to the powder used. 150 fps increase or reduction in velocity with cause MASSIVE vertical dispersion past 150-200 yards. And can be measured in FEET at 300 yards. BTDT. Even with the Goex of 25 years ago it required an error on the shooters part to get variations this large.
So far as the powder the barrel will burn? They will burn a lot unless very coarse powder is used. Now there IS a point of diminishing returns. But this has has little to do with what the barrel will burn and nothing to do with the load that will be most accurate in a given barrel.
Dan
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..... nothing to do with the load that will be most accurate in a given barrel.
Dan
Thank you for bringing some sanity back to the conversation. :D
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So if you have a longer barrel, yes you can get the ball to travel faster from a 48" than from a 32", as long as you have more powder.
Oh geeze, silly me, of course just add more powder!
Except I guess I thought the discussion was the difference in velocity between various barrel lengths, and not the differences between various barrel lengths with various powder charges,,,,,,,, That's waay to complicated for my simple brain on a hot Saturday morning, so I'll go back to drinking my coffee! ;)
John
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Here is a link to a site that puts things in an understandable form. Notice that QuickLOAD is referred to. The author of the article thinks that Q/L is over priced. I have sold over 10,000 copies to handloaders who consider a bargain. :)
http://www.frfrogspad.com/intballi.htm
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It's only overpriced if you don't use it. ;D
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True. I have been googling to find the volume of gas generated by a given amount of FFG. Armed with that info, it is a simple math problem to calculate the length at which max velocity is reached (volume of gas equals volume of chamber[barrel]) and the point at which everything comes to a screeching halt.
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As long as there is pressure behind the ball it will be accelerating - until the engraving forces/friction are greater than the pressure. At that point the ball will begin to decelerate. This is most likely going to become significant in barrels which are very long for the caliber and impractical for general use and for other factors such as extreme vibration/accuracy issues. As long as you hear a bang there is still pressure behind the ball when it exits the barrel. But there is some length after which there are no significant gains in velocity and that probably happens before 40 inches. It typically happens around 30 inches in modern rifles and the gain of another few feet per second by carrying a few more inches of barrel around just isn't worth it. Even Weatherby gave up after 26 inches of barrel in their custom rifles firing very large charges of progressive powder which could make maximum use of the extra length.
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You have to figure that this experiment has been done a lot of times over the years. A few minutes surfing the yielded the following:
http://powderburns.tripod.com/powder.html
Velocity gain per inch of barrel beyond 28 inches is approximately 8 fps per inch, declining gradually until at about 42 inches there is no velocity gain from increased barrel length. Velocity may be expected to drop as bore friction negates the velocity gains of an increased charge.
This reference cited someone named Ed Yard, who did the work for Thompson/Center Arms. Unfortunately, this source didn’t give any references so I couldn’t check out the original data.
From a thread on another site:
Per the Lyman BP Handbook:
26" --- 1574 fps
28" --- 1587 fps
32" --- 1663 fps
43" --- 1725 fps
This gives us a gain of 8.9 feet/second per inch of barrel length. I don’t have the Lyman book, so maybe someone will want to check the raw data.
From Rice’s site, with 30” to 44” barrels, I calculate a gain of 9.3 feet/second per inch of barrel length.
All three barrels were .50 caliber.
So, from three different sources, we find good agreement: 8.0 fps, 8.8 fps and 9.3 fps gain per inch of barrel length.
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Joe S.
Something appears to be wrong with the numbers you cite. from 26" to 28' the velocity increase is only 6.5 fps per inch. But from 28" to 32" the increase was 19 fps per inch. Then the last increment from 32" to 43" the increase is only 5.6fps per inch. The only way you get a 8+fps per inch increase is averaging of the entire length change. That doesn't make sense either as the numbers from 28 -32 inches are clearly inconsistent with the other two data points. Might want to revisit your reference to be sure the loads being compared are the same.
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The problem with lyman's data was the powder used.
Goex of the time might vary enough from can to can or even in the same can to screw up the data when dealing with only a few FPS.
So the loads tested for the 32" length may have been with better powder/new can/can just opened vs toward the end where it may have been 15-25% semi-combustible dust.
I made some statements about velocity variations in a previous post. I should have pointed out that some lots of powder before I switched to Swiss were so bad that it was not unusual to throw away a significant portion of each can. I did not use the fines in last 1/4 to 1/8 of the can. Now if people did not KNOW this and were shooting a ML where it would largely go unnoticed then high variations in velocity might occur.
If the barrel length vs velocity thing were done with current production powder, Goex, Swiss, Schuetzen for example the results would likely be more consistent or perhaps more linear.
Dan
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If all the powder has been totally consumed in whatever length of bbl achieved this condition, then each addt'l inch of of bbl length would provide only friction which would decrease velocity. Once the pressure decreases, there's no addt'l force exerted on the projectile and then bbl friction would decrease velocity.....Fred
I knew of a experiment where the fellow took a barrel of many feet and shot a 32auto round in it.....it went off and stopped due to friction after about 12 feet.......
I want some of those military rounds that find the green laser lighting up the target >:-)....self-correcting-rounds outta a 50cal.................wow!
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Jerry
There is nothing wrong with my numbers. As with any data set, there are a variety of ways we could choose to analyze the data. In this case I chose the simplest, which is (maximum velocity – minimum velocity) / (maximum length – minimum length). This gives us a good ballpark average of the effect of barrel length on velocity.
There are of course, other ways to approach the problem. The “best” would be to use nonlinear regression, which would give us a polynomial equation of the general form y = m(exp) + bx + c. I chose not to do this for two reasons: 1) most of the folks here would not understand how to use the equation, and 2) it would lead you to exactly the same conclusion that the simplest analysis does.
That conclusion is of course, for barrel lengths between 28 and 42 inches, barrel length has no meaningful impact on velocity. For hunting purposes, I could shoot deer with a 28” barrel or a 42” barrel, and I could kill deer all day long with either gun. If I happened to hit an inch or so higher or lower than I intended, the deer would be just as dead. If you want to shoot targets with Dan on the high plains desert where wind drift is a major factor, get bigger balls.
There is one really important feature of these data sets that you should notice. As Dan pointed out, there are a number of important variables that were not controlled. These include powder type (even to batch level), ball size, patch thickness, temperature, humidity and lube. Yet in spite of lack of control of these variables, all three tests show about the same effect. That is, for each inch in barrel length, the average change in velocity is on the order of 8 – 10 fps per inch. Or, roughly speaking, going from 28” to 42” will give you a velocity gain on the order of 100-150 feet per second.
We could of course, repeat this test with rigorous control of all the variables. This wouldn’t help much because it is a forgone conclusion that you gun is going to be different than the test gun.
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Velocity gain per inch of barrel beyond 28 inches is approximately 8 fps per inch, declining gradually until at about 42 inches there is no velocity gain from increased barrel length. Velocity may be expected to drop as bore friction negates the velocity gains of an increased charge.
This is the quote that I have a problem with. Since it is not put in context it is impossible to tell how the author arrived at this conclusion. This may be the case with a fixed powder charge, but I find it hard to believe that this is a hard and fast rule. If charges are increased, then it appears obvious that you can take advantage of longer barrels and gain velocity.
If it is an accurate statement of fact then why choose to post it? Am I missing something??? Enjoy, J.D.
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Thanks JDK, I thought it was me.
Robby
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It's about the effiecent burning of the powder. If we put a 100 grs in a 20" barrel it would puke a bunch of it out the other end. The same 100 in a 48" barrel would use much more of the powder & consequently produce much more velocity. Does the dead deer care, not really. But it's still the same conclusion that the same charge in short barrel is slower that in longer barrel up to the point where the steel is longer than the powder will produce pressure.
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I recently added a 50" Getz .540 smoothie to my meager collection. I've never shot her through a cronie,but she shoots real flat with a 80gr. charge with a .515 RB and a .025 lubed patch. I'm wondering if there is a diminishing return in a smoothbore and at what point? ( I sure had fun with this gonne at our annual Provincial meet at Heffley Creek!)
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I'm wondering if there is a diminishing return in a smoothbore and at what point? ( I sure had fun with this gonne at our annual Provincial meet at Heffley Creek!)
At less than 100 calibers long & 80grs I would think this charge is still doing fine. Translate the numbers to a 36 cal at 35" long or so. It would sound perfectly logical.
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Joe S,
If all you are trying to determine is an average change of velocity per inch of barrel you are chasing a useless number because we both know any correct answer has to be a diminishing returns curve, not a straight line (linear) value.
I think the original question was about breech pressure which many think of too simplistically equating it to velocity and recoil. The real issue is the area under the time vs pressure curve on the chart as that area represents "work" performed accelerating the ball. That area clearly diminishes as the time progresses so velocity increases would diminish in a parallel fashion. There is not going to be a definitive single value for velocity increases versus barrel length. Every barrel, caliber, powder charge, ball, will give a different value.
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We need to ask ourselves what the question is.
If its "Why were the 18th c barrels so long? To get a REAL answer we have to either step back in time and ASK Andreas Albright OR make 18th c powder maybe with a mortar and pestle then force the damp powder through screens, by hand, to form a grain size. For most of the 18 th c powder was not made in the same manner as in the late 18th to early 19th when improved methods really caught on and "modern" BP started to be made.
So if we have a slow to very slow powder with large (relatively) particle sizes, not very consistent from poor grinding technology we can expect a longer burn time with a longer, I expect, pressure curve and the need for a longer barrel. Also as it got older the powder tended to get finer since the stuff tended to break down easier.
This is a complex subject and the only way to REALLY know is to make some powder. Something I have no intention of doing.
As we progress to wheel mill powders we get finer particle sizes and a faster burn rate and compression starts to be used to control burn rate somewhat. This is one reason some lots of Elephant were so slow, they use too much pressure when they pressed the damp powder.
We do KNOW that the modern powder making of the late 18th and early 19th which means the use of wheel mills for grinding and the powder being pressed into cakes then broken to form granules resulted in MUCH better powder than stamp mills (they used what were essentially giant mortar and pestles driven by water power, a wheel driving perhaps 10-20 such machines) so they could shorten barrels.
So if we want to know the MODERN reason for longer barrels its APPEARANCE. Its not possible to make a nice John Armstrong with a 26-28" barrel.
Also longer barrels produce better accuracy with non-optical sights (so those really long chunk gun barrels) and they tend to hold better offhand which also produces better shooting.
My handiest hunting rifle is my Manton like 16 bore rifle. My best offhand rifle in a toss up between my 38" Don King Hawken and my 40" swivel breech.
And finally the long barrels in some cases may have simply been habit. Long barrels were needed to they made them long.
But wait!!!
There were short barreled rifles in the early 18th and even in the 17th c.
All I know is that its a tempest in a teapot.
By the second quarter of the 19th c large bore British sporting rifles were 30" or less in many cases since they often were hunting dangerous game in heavy cover in some parts of the Empire.
Reading Forsythe and using his carefully determined trajectory table to 100 yards I know that his 26"+- inch 14 bore rifle with a 15 gauge ball gave practically the same velocity with 137 gr "Hall's #2" powder as my 30" barreled FL rifle using a 16 gauge ball.
Back to velocity variations.
In lymans book IIRC they used the same barrel and shortened it as they went through the barrel lengths.
So...
If they shot this barrel a lot by the time they had progressed to the shortest barrel lengths the bore could have become smoother as so the velocity my HAVE BEEN LOWER than it might have been had the barrel been cut to 26" or whatever and shot when brand new since a nice smooth barrel produces LESS velocity than a one that is slightly roughened especially at the breech (this has been known for a very long time and the British used this to increase penetration (velocity) in shotguns but its harder to remove the fouling). They would also roughen them slight at the muzzle to "retard the wads" to stop them from being blown though the shot and spreading the pattern. So if the barrrels finish improved with shooting as they tend to do then Lymans data is not 100% reliable.
So with modern powders the break point is PROBABLY about what Joe states, in the 28-30" range. Based on my readings and personal experience I would have guessed it was about 30". By break point I mean the point at which the increased barrel length gave less and less gain.
Killing power?
I KNOW that a 50 caliber round ball will shoot through a deer or antelopes chest cavity at a striking velocity of 800 fps give or take 20 fps. I have done it with a FL pistols. I have shot through deer with a 50 caliber rifle with 1/2 ball weight of FFF to 150 and have done penetration tests to 200 that indicate it will STILL shoot through a deer at this distance.
The key is and was trajectory (for rifles for shotguns it was penetration) and this was written about at some length by Forsythe. Higher velocity makes for a flatter trajectory. This is very useful to the hunter but is largely meaningless to the target shooter.
So did they make the long barrels for velocity, or sight radius, or how the gun looked? I think it was to make use of what we today would call very substandard powder and later from habit. It was how things were supposed to me. By 1830 in American we have rifles with barrels in the "40s" and barrels down to 30" or so. Probably depending on the local preference or that of the person buying the rifle.
To me the best COMPROMISE is going to be 34-36" it will give best velocity/sight radius/offhand hold COMPROMISE. From a modern stand point. How it would be viewed in 1770 by someone making rifles in Eastern, PA is not something I can speak to except say most American rifles of the time were long barreled and to make a rifle that is typical of the era its gotta be 40" or more.
If the "modern" wants a hunting rifle that is the best compromise then read Forsythe. He will tell you 26" of so in plenty long enough. Something like what Joe stated.
Dan
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Nailed it, Dan. APPEARANCE. To my mind, if traditional appearance--for whatever period and location--is not important, then we might as well all be shooting black stocked stainless barrelled saboted slug
inlines (can't say that word). We're about American LONGrifles here, with some tolerance for smoothbores, pistols, Germanic/English guns from time to time.
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Yeah, but my black composite stocked SS Firestorm flinter is my "PRB assault rifle" ...
It 'assaults' the feelings of my fellow shooters! ;)
Cheers,
Smoketown
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My favorite black plastic stocked rifle shoots 1/2 MOA at 400 yards in limited testing. Will shot about MOA at 400 in actual matches.
The other one shoots under MOA at 100 never put on paper at 200, its just a backup hunting rifle when the hunting is hard.
But they are just tools really and have no aesthetic value.
Dan
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I forgot to put in Forsythe's velocity. 1600 fps by matching his trajectories with a ballistics program.
Dan