Barrel length and velocity?

[Sparkitoff]

First, I'm putting this in the Percussion category because I am specifically referring to percussion rifles and I understand that flintlocks have different dynamics that would not compare directly to percussion rifles.

I've heard many times that the barrel length affects velocity. What is often written is that with the same caliber and load components the longer a barrel the more velocity to some point and then a taper off where the length no longer contributes.

What I am experiencing is virtually no change in velocity from length to length with the same components. I have a 24" barrel, a 28" barrel and a 34" barrel. I am using 80 grains of the same powder, dry-lubed patch and ball. There is virtually no change in velocity when looking at 5-shot averages over the chronograph. There is less than 60 FPS difference between the slowest and fastest shot, which to me is insignificant. The average deviation is 28 FPS so 60 FPS is not far out of bounds.

The one difference in these rifles is ROT. The 24" is 1:48, the 28" is 1:60 and the 34" is 1:70. Since that is the only variable other than length is that the cause and effect?

I have read about different ROT allowing for more or less velocity based on greater or lesser powder charges, but these are all being fed the same.

Obviously, this situation is not a "problem", I am just curious and seeking to learn.

Thanks

 

[Carbon 6]

I think it's more a function of utilization. Using today's powder in the amount you are using you are achieving full utilization.
Grade and quality of powder has been extremely variable in the past. It is my thought that longer barrels were needed to utilize slower burning and poor quality powders.
There are written references to powder quality and it's affects by balisticians of the day.
I also think that your test does not take advantage of barrel length. your maximum difference is only 10 inches. Although that ten inches shows what? A 60fps difference. To me that is significant.
If you are looking for a linear change in velocity/inch I don't think you'll find it.

If you repeat the test but change the powder to a larger granulation, I'll bet you'll get some interesting data.

The one difference in these rifles is ROT. The 24" is 1:48, the 28" is 1:60 and the 34" is 1:70. Since that is the only variable other than length is that the cause and effect?

Do the guns all have the same breech design? and, did you use the same nipple for each test?

 

[longcruise]

You are dealing with the possible variables and variations between the three barrels. If you take one barrel and shoot it while gradually cutting the barrel shorter you will be seeing the results of the one variable of barrel length.

However, to save yourself from ruining a barrel, Rice barrels used to have the results of such a test on their website. It's probably still there.

 

[Zonie]

Years and years ago, Dixie Gunworks tested the effects of shortening a barrel using different powder loads.

To do the testing they used one .40 caliber percussion barrel, loaded with 10 different powder loads ranging from 38 grains to 120 grains using DuPont 3Fg powder under a patched roundball.
After firing 5 shots with each of the 10 powder loads load they averaged the muzzle velocity of each load to obtain the velocities they published.

After shooting the 10 loads, they cut 2 inches off of the barrel and repeated the 10 different powder load/5 shot testing and averaging.
Starting with a barrel that was 40 inches long, they continued shortening and testing the barrel until it was cut down to 20 inches long.
They quit testing the larger powder loads with the shorter barrels when they felt the muzzle blast "became objectionable."

Looking at their data, there is no doubt that shortening the barrel reduces the muzzle velocity .
For instance, looking at the data for the 94 grain powder charge, the largest that was tested thru the entire 40 to 20 length barrel the velocity dropped from 2260 fps to 1976 fps.

 

[PluggedNickel]

I tuned into this one just too read Zonie's reply. Thankfully, he didn't use quantum physics or too much math, and I already knew length with no other variables would change velocity. I just didn't know how much. So thanks and KUDOS to you Zonie. I didn't get a headache trying to digest this post!

 

[hanshi]

The longer the barrel, the more the velocity...sometimes. Barrel length and velocity is NOT a linear effect. A 44" barrel may give 2000 fps; but when shortened to 39" it may give 2078 fps. This is just an example of what can happen with any given barrel.

 

[tenngun]

Looking at the velocity tables in Lyman’s muzzel loading handbook you see increased velocity with longer barrels... in general. However not big payoffs at any range. When TC came out with their Hawkens they settled on a 28” barrel, because on average they only they saw a 10 FPS increase for an inch of barrel charge for charge.
I don’t like short barrels and just sold off my short gun, a 36”. However it’s taste, not performance.

 

[Poboy]

Well, a couple of things. Actually, while people think of black powder as "slow burning " and smokeless as " fast" put a thimble of each in an ashtray and touch them off. The black powder will go up in a blinding flash, while the smokeless will fizzle to and end.

Now, what this means to the discussion at had is this: much as the confusion on high octane gasoline goes, higher octane in fact, burns slower. Sooo, logic tells us that smokeless powder barrels should produce more velocity while black powder, not so much.

BUT!!!!! The burning of the powder charge, is only part of the equation. The principal physics is that an exploding powder charge creates expanding gases, which are what causes the bullet to exit the barrel. So, again the longer the barrel, the more the bullet is going to benefit....UNTIL!!!! The barrel length exceeds the volume of the expanding charge, at which point, the drag of the patch, rifling, ect....begin to scrub off the gains of utilization by the longer barrel.

Sooooo....those are the reasons, and why there aren't any set in stone answers.Now, take the knowledge and apply....

 

[Zonie]

IMO, your comment about the speed that smokeless powder ignites is a bit off base.

The speed that smokeless power burns is dependent on the pressure around it.
While it just fizzles under normal atmospheric pressure under 15-20 thousand psi it burns much faster than black powder does. One might say, under 20,000 psi of pressure it almost explodes.

Black powder on the other hand burns at the same, explosive speed whether it is inside a barrel or just sitting on your sisters bicycle seat. (A small reference to Pat McManus's experiment and his singed eyebrows. )

 

[Bad Karma]

Kudos for the information but mostly the “Poof! No Eyebrows!” Reference...

 

[Poboy]

IMO, your comment about the speed that smokeless powder ignites is a bit off base.

The speed that smokeless power burns is dependent on the pressure around it.
While it just fizzles under normal atmospheric pressure under 15-20 thousand psi it burns much faster than black powder does. One might say, under 20,000 psi of pressure it almost explodes.

Black powder on the other hand burns at the same, explosive speed whether it is inside a barrel or just sitting on your sisters bicycle seat. (A small reference to Pat McManus's experiment and his singed eyebrows. )

Fair enough, but.....much like the gasoline octane analogy, ummmm, yeah, .... so?

You do have to have to have slower burning ( higher octane fuel) in what? Higher compression engines. Now, that is more to do with ignition point, but, we are getting far afield. The point was, ( and I understand yours) is that is a bang that creates expanding gasses, and...there is a limit to the benefit of a length of barrel to harvest it.

Now, again, logic dictates that a blackpowder rifle should be able to maximize that faster burn time as it should utilize all of it. BUT, now, you say modern smokeless powders burn faster under pressure.

Maybe why we don't have cops carrying BP pistols? But, seriously, it does bring up another interesting angle to investigate. No argument that modern smokeless generates more pressure and probably utilizes more of the pressure charge in barrel length ( ironically, by burning faster) but brings up the same question of barrel length vs. velocity.

Soooooo, just in case we haven't derailed this thread enough, which firearm suffers velocity loss less with shorter barrels and why? I say BP.

 

[Sparkitoff]

I'm not sure a direct answer was provided. I appreciate the input. What I am gathering based on the responses is that if I were to cut one of these barrels the velocity would surely drop, but the 3 lengths compared to one another really don't correlate because each has a different amount of "pressure" based on actual bore diameter, rifling lands and grooves, etc. Is this about right?

 

[Zonie]

... the 3 lengths compared to one another really don't correlate because each has a different amount of "pressure" based on actual bore diameter, rifling lands and grooves, etc. Is this about right?

I think that's pretty much it in a nut shell.

 

[Melnic]

My $ is on the fact that the OP's test had 2 variables and not just one.
60FPS is what? 3% change?

 

[PluggedNickel]

IMO, your comment about the speed that smokeless powder ignites is a bit off base.

The speed that smokeless power burns is dependent on the pressure around it.
While it just fizzles under normal atmospheric pressure under 15-20 thousand psi it burns much faster than black powder does. One might say, under 20,000 psi of pressure it almost explodes.

Black powder on the other hand burns at the same, explosive speed whether it is inside a barrel or just sitting on your sisters bicycle seat. (A small reference to Pat McManus's experiment and his singed eyebrows. )

Loved Pat McManus, read most of his books. Funny, doesn’t take himself to seriously. Makes you know it is OK to be human, and even the best and brightest of us do ....head up butt, stupid things at times. It may take a spell before we can laugh about it, depending on the screw up, but the sooner you can, the better off you’ll be. It would make a great thread. “What is the worst disastrous screw up you ever made?” I wonder how many would tell the unvarnished truth?

 

[Sparkitoff]

Really the max variation was 60 FPS from the slowest to fastest shot overall so the mean variation is closer to 30 FPS variation barrel to barrel.

Thanks for the help!

 

[tenngun]

Looking at Lyman’s data that tested several barrel lengths in each caliber we do see a general trend but no where near enough change to be a 1:1 correlation that 1” equals 10 FPS for a given charge/ patch/ball/lube combination
At some combo extra barrel length slows the velocity, while high charges it can increase30-40 FPS per inch. What is the payoff though?
A .40 as tested by Dixie at 1900 FPS and at 2200 FPS will both slow to about 1700 FPS at 25 yards

 

[longcruise]

I thought Zonies data was very interesting. I'd like to see the full set of data. The difference between the high and low charge at the end of his post way much less than I expected.

 

[Carbon 6]

I don't see any practical usefulness to barrel length velocity data. it's not like our barrels telescope or anything. We load for accuracy not velocity (except for shotguns maybe). Most people I know choose length based on style or model and fit. Not to many 14" long rifles or 48 " Hawkins out there.

 

[Poboy]

Loved Pat McManus, read most of his books. Funny, doesn’t take himself to seriously. Makes you know it is OK to be human, and even the best and brightest of us do ....head up butt, stupid things at times. It may take a spell before we can laugh about it, depending on the screw up, but the sooner you can, the better off you’ll be. It would make a great thread. “What is the worst disastrous screw up you ever made?” I wonder how many would tell the unvarnished truth?

No can do...that would get me locked up. Either in jail or the funny farm.