Intersting round ball barrel ballistics

[zimmerstutzen]

Figures are from the Lyman Black Powder Handbook 1st ed.

peak pressure for 60 grains in a 45 caliber barrel
in Lead units of pressure
28 inch, 5,660 LUP
40 inch 9,140 LUP
43 inch 9,720 LUP


substantially more peak pressure in longer barrels. Even with such a moderate load, peak pressure increases between the 40 inch and 43 inch bores.

compare the figures for the same charge in a 54 caliber barrel

28 inch 4,860 LUP
34 inch 6,800 LUP
43 inch 7,000 LUP

the same trend is apparent.

I would have thought the Pressure in the 54 would have been higher because of the much heavier ball. I also never expected the pressures in a 45 to be so high with a moderate load like that.

Just thinking out loud, but it seems like heavy loads would be more dangerous in a longer barrel than a short barrel. Not that I would ever push that limit anyway.

[BrownBear]

I'm more surprised by the increasing pressure with barrel length than the comparison of pressures between calibers.  Unless Lyman too is guilty of keyboard ballistics in assigning the same bore and groove diameters to three barrels, they were clipping the same barrel to get different lengths, making the comparisons useful.

As for large caliber versus small, that's always been my experience with cartridge guns, both in reading and doing my own checking when I've had access to pressure equipment.  Pro ballisticians I know and have worked with attribute the lower pressures in larger calibers to the larger surface area on the rear of the projectile and the comparatively larger than long powder column or "chamber" in the bigger bore.  I.e., the diameter and length of 80 grains is going to be substantially different in a 45 cal than a 54 cal while pushing on a much larger surface as the powder ignites.  There's less surface resistance of the projectile against the bore wall compared to weight with the larger diamter, so it takes less effort to move it. And the long "skinny" powder column in the smaller bore burns differently than a short fat one.

[Daryl]

Increased length equalling higher pressure, all else being equal is interesting.  Note that throughout the book, when velocities are similar, so are the LUP pressures. A .50 cal. at 32" running a round ball at 1,800fps is producing roughly the same pressure as a .58 with 32" producing the same velocity - now, check the powder charges needed in the .58 - is that interesting or what?

Due to that book, back in the late 70's, early 80's, I tested my .58 heavy barreled Hawken all the way to what Lyman shows and at that time, but recored slightly higher velocities. The lubricant used makes a BIG difference, especially in velocity and shot to shot velocity variations.

[Dave Faletti]

There is something missing or flat out wrong with that data.  Peak pressure will not increase because the barrel is longer.  That makes zero sense.  They were comparing different barrels or got their numbers scrambled.

[BrownBear]

There is something missing or flat out wrong with that data.  Peak pressure will not increase because the barrel is longer.  That makes zero sense.  They were comparing different barrels or got their numbers scrambled.

I think you're right.  Looking at the Lyman 2nd edition, their selection of barrel lengths in other calibers is not as great, but in 54 and 58 caliber there are a number of barrel lengths and they report no such trend. 

[Daryl]

Dave, there are other annomolies in the data - so mixing data is quite possible.  Too- they used the same barrel in each calibre, I think, reducing the length for each barrel length data stream. I agree the pressure averages should have been quite similar throughout the test.

One thing I noticed that really stood out, was the difference between the Lyman data with 24" barrel with what I achieved in my own .58 24" bl.  Their 70gr. 2F GOX velocity was some 300fps slower than what I achieved with only 5gr. more GOEX, ie: 75gr. Indeed, they also recorded lower speeds with the same charges in longer barrels, in that .58 calibre, which seemed interesting as well. 

Now, we know the larger the bore, the shorter the barrel can be & still remain efficient due to expansion ratios in larger holes, however I'd not have thought the 24" bl. would outshoot the 32" with most all loads.  It is possible that much mixing of data while recording is responsible for these non-logical results.

[bgf]

Same pop in a smaller space = higher pressure , so the decrease in peak pressure with caliber increase is reasonable, and I thought was the accepted "truth".  Increase in peak pressure with a longer barrel makes no sense.  I could see it if pressure were integrated over time, but that wouldn't be peak pressure.  What exactly is Lead Unit Pressure (LUP) and its method of measurement?  Is it possible these results are the artifact of their measuring device or the definition of LUP?

[roundball]

There is something missing or flat out wrong with that data.  Peak pressure will not increase because the barrel is longer.  That makes zero sense.  They were comparing different barrels or got their numbers scrambled.

Agree...and by far, not the first time that errors have been noted referring to Lyman's 1st edition.

[billd]

Rice tested a 50 and got more speed with longer barrels.  Doesn't it take more pressure to make more speed?

Bill

[zimmerstutzen]

The fact that the pressure curves seem to reach higher peak pressures in the longer barrels makes it sound like the powder is still burning and increasing pressure even when the ball is 26 or 32 inches down barrel.

 

[Daryl]

I see that as the longer barrels give the expanding gasses, longer to act upon the ball's base, thus increasing the speed.  I suggest ALL the powder is burnt quite early in the barrel and that it is the perios of time the expanding gasses of the burnt powder have to act upon the ball, is what increases the speed.

As far as lead units of pressure - I seem to recall Lyman said they used lead crushers as copper crushers were not consistant at such low pressures - ie: less than 15,000 CUP, hense the use of lead.  How those lead numbers  correspond to actual pezio pounds per square inch numbers, I've no idea - but the suggestion is there that they are comparable.  It is quite probable that the 'conversion' charts in LUP would represent CUP or PSI quite easily.

We do know that straight case CUP and straight case PSI #'s are very close, and in some calibres & cartridges, they are virtually identical.  For instance, .357 mag  & .44 mag pistol #'s coincide, as do .38/55, .45/70, .458 mag, .458 Lott etc.  On the other hand, bottle necked cases on the other hand, can show very large differences in the numbers generated and are not mathematically comparable. There is no way to accurately change one to the other.

 What does this have to do with us?

Thus, straight cases giving virtually the same number are important to us. Our barrels are litterally straight ctgs. in which we load powder and ball as if placing it in a ctg. Thus CUP and PSI generated in our barrels are virtually the same number - now, are LUP #'s the same as well?  That's the million dollar question.

 If we look to shotgun data, we see this seems to be the situation - at least close enough for 'rough' use. There are no absolutes as variations in loads changes the delivered 'goods' instantly - tight, loose, granulation change, powder make change, different compression of the powder by the ball, the size of nipple hole or vent, make and designation of percussion cap, etc. 

However, rough use is all we need for our purposes. It works.

Gas leakage at the breech can make for quite large speed differences, gun to gun. We're told 200fps is common.

[roundball]

Rice tested a 50 and got more speed with longer barrels.  Doesn't it take more pressure to make more speed?

Bill

Its a case of there's already enough pressure to begin accelerating the projectile...and as we know, the acceleration stops at muzzle exit of course, so different barel lengths will give different velocities with the same identical load, depending on how long they're able to continue to accelerate...until muzzle exit.
There is probably also some point of diminishing returns where if a barel was long enough and/or the powder charge small enough, that friction begins to have more of an effect than the declining push of the decaying pressure curve.

[hanshi]

In reading a researcher's figures measuring pressures with a transducer, the figures were quite different from what Lyman gathered and were much more consistent - this was in an old Gun Digest.  I'm guessing there's a problem with Lyman's methodology or either these were misprints.

[longcruise]

I've always found  much to disagree with in Lyman's numbers!

Okay, who has an Oeler Ballistics Lab??

[bgf]

In the Wikipedia article on CUP (and LUP), there is this statement:
"Since a longer duration, lower pressure pulse can crush the cylinder as much as a shorter duration, higher pressure pulse, CUP and LUP pressures frequently register lower than actual peak pressures (as measured by a transducer) by up to 20%.

I would guess what is happening with the Lyman numbers could be related to that observation: the longer barrel has pressure for a longer time, so the lead crusher guage registers higher pressure than the shorter barrel.  Interestingly, I would say this is not really "peak" pressure but some function of pressure and time -- though the distinction is academic; my guess is the peak pressure is exactly the same, and there would be no concerns safety wise with the longer barrel vs. a shorter one.  It is for the same reason that longer barrels produce higher velocities (pressure applied for a longer time), so even the distorted pressure reading could be useful in a way, if looked at for what it is.

[Dave Faletti]

The pressure pulse they are refering to is the short duration about the peak.  A small amount of fast burning may have a peak that lasts 10uS.  Defining the pulse to be the time interval where the pressure is still greater than 90% of peak.  A much larger amount of slow burning powder may have a pulse that lasts several times that but it still amounts to the point where the bullet is only a short distance down the bore.  Once the crusher starts to deform it doesn't take as much to continue for a moment.  Dynamic and near static loading on crushers do not correlate real well.  The intention was for it to be psi which is why it seems to equate.

[Daryl]

You - and they are right bgf - in bottle necked cases. If you research you will find what I said to be correct. In the straight cases the numbers for CUP and PSI are the same. I am also saying the straight barrels of our guns are quite similar if not exactly so, ballistically to a straight case - logic says this is true, along with cross comparrisons to shotshell pressures.

[doug]

     any pressure curves that I have ever seen have shown maximum pressures to peak within the first 10 inches of the barrel.  In other words the pressure at the breach should not increase with any barrel over 10" and probably any barrel over 6 or 8 inches.  I think the increased pressure is an artifact of a long slow low pressure crush in a longer barrel

cheers Doug

[Dphariss]

This is Mad Monk territory but here goes.
This is from a post on another web site where members were inflicted with the same "revelation"


There were SIGNIFICANT variations in powder from can to can (or even in the same can) in the time frame we are discussing (I was using quite a but of powder at the time in competition.) As a result there is no way to draw conclusions. Its impossible. There could be significant pressure and velocity changes within the same can of powder and certainly from lot to lot.
So... Did the maker pack one can/case/lot of powder with just a little more moisture content? Did they put just a little too much graphite in the drum when "polishing" the powder? Was the steam used to stick the graphite perhaps a little too much? Did they make one lot of powder during a period of little rain fall? This increases the concentration of SULFUR OXIDIZING BACTERIA in the water. Then when making powder with the water the bacteria EAT the sulfur starting when the water is added and the powder tends to turn to dust IN THE CAN. Were the can lids loose? Many were and as long as the oxygen level is high enough the bacteria would be at work. If sealed the bacteria would eventually go dormant until the can was opened. So back before Swiss the first thing done when new powder arrived was to tighten all the lids.... Yeah.
The "bugs" and having a slightly too high moisture content was why some cans of powder had rust from the can mixed with the powder. I have heard reports of cans developing holed from the inside out due to rust.

Back before the move to Minden throwing away 1/4 of a can of Goex powder was "normal" since there was that much dust in the cans of some powder lots. This will not be apparent in loading a ML but in loading BPCR ammo with a drop tube its very apparent since the powder falls faster than the dust. So when dust appears in the cartridge case the powder is thrown away and a new can opened. The dust, for whatever reason settled in the bottom 1/3-1/4 of the container. So pouring it into a powder dispenser like a Belding and Mull or RCBS etc. allowed the dust free powder out first. It was not really apparent until drop tubed.

I seriously doubt that Lyman knew of or even noticed the dust and if they did it was afterall "normal". ALL the powder did this to some extent.
Even the grains that are not destroyed are more porous and this changes the burn rate. They were weak and would crumble then the load was rammed on a ML.
This was a problem from the time Dupont shut down the boilers and stopped using distilled water (the standard back in the day) in the process. It had serious effects on the powders performance in firearms, as fuzes and and booster charges in propellants. In fuzes and boosters, I have read, there were serious "events". I do know that during my time in service, for example, we had all baseball grenades picked up since they had some with "instant" fuses, this is not desirable in hand grenades. Years later I learned there was a lawsuit against the powder maker. Yes, grenade fuses are made with BP.
The move to Minden eliminated the bacteria problem, no sulfur oxidizing bacteria in LA it would seem and a change in suppliers eliminated the problem with impure saltpeter, this also causes significant performance variations since its impossible to maintain the proper moisture level in the powder. So from the chemical standpoint Minden powder is superior and overall is superior to powder made at the Moosic plant in PA.
Having some sodium in the saltpeter was why some lots of powder used to suck up humidity and get relatively "wet". Extra moisture, even 1%, will significantly effect performance.

So given the possible powder variations variable results are going to be the norm. If Lyman had BLENDED 200 pounds of powder and sifted all the fines out their results may have been more consistent.
I have no idea why the numbers came out as they did.
But I suspect it was powder quality related.
OR, and this just occurred to me, it might be bore condition related, at least in the first edition the barrels were shortened to provide the additional barrel lengths. So the 43" barrels were brand new and the 32" barrels were much older having had something in the realm of 700+ rounds fired by the time they were cut to 32".
A slight roughing of the bore will create higher pressures and velocity. So with all the testing done is it possible the bores got a little rougher by cleaning all at once at the end of the day and barrels were allowed to set uncleaned as testing with other barrels was carried on? ALSO the bacteria by products in the powder may have increased the aggressiveness of the fouling so far as attacking the barrels is concerned.
THIS bore condition change scenario is one I could understand. But its supposition or course.
 Even if not noticeable the increased friction this creates WILL increase pressure and velocity.
It was a trick British ML shotgun makers used to use to increase penetration (velocity). They would slightly roughen the bore near the breech to retard movement of the wads and shot thus increasing powder efficiency.

Dan

[FL-Flintlock]

Crusher gauges are completely unreliable for firearms applications because it's impossible to identify if one is reading an accurate actual peak pressure or the time lapse exposure.  Something else to consider is how the particular load combination functions in a given barrel length.  While I haven't seen any data on BP loads, it's common knowledge in the nitro world that certain load combinations with certain powders are prone to producing SPS (Secondary Pressure Spikes) in longer length barrels that can be far higher than the safe operating pressure of the load produced in a shorter barrel.
Mark

Interesting, Mark - but I seriously doubt SPS has anything to do with the black powder pressure data Lyman produced in the 70's.  As to the bore wear or roughness producing increased pressure, the shorter barrels should have produded higher pressure - yet the reverse shows in the Lyman data.

The data is quite screwed - or squerred or something. OK- expample .54 w/same ball, powder, patch, lube as longer barrels: 28" = 10,890LUP" 30" =  10,440LUP:  34" = 12,200LUP:  43" = 11,700LUP  ZUPWIDAT?
Incidently, in the 28"- in order to get 10,610LUP with C&H 3F, it took 180gr. and 190gr. produced only 11,200LUP.
The 34" 100gr. 3F pressure with round ball is duplicated using 410gr. slug and 190gr. C&H 3F. Cool-not- but the comparrisons are interesting.