Velocity Increase/Loss per inch of barrel

[Artificer]

Has anyone done a definitive test of how much velocity is lost from a muzzle loading barrel firing a .45 or .50 cal. PRB with black powder (not a BP substitute) as the barrel is shortened one inch at a time from say a 42 inch length down to 20 inch length?

I am referring to using the SAME barrel, with the SAME powder charge, with the SAME size ball and patch and lube. IOW, the only thing that would change is the length of the barrel?

If someone has, please let me know the results per inch of velocity loss.

Gus

 

[longcruise]

Rice barrel company did such a test. The results are on their web site. I can't place links on my phone, but just google rice barrel company.

 

[Loyalist Dave]

I don't know if it was done with a ML barrel...I've seen it done with fixed cartridges

LD

 

[George]

The Rice test link:
http://www.ricebarrels.com/velocity test.html

Spence

 

[Artificer]

Rice barrel company did such a test. The results are on their web site. I can't place links on my phone, but just google rice barrel company.

Thank you VERY MUCH!! :thumbsup: :hatsoff:

For others who are interested, here is the link:
http://www.ricebarrels.com/velocity test.html

So by cutting off 14 inches of barrel down from 44" to 30", the velocity loss was on average 130 FPS total loss or less than 10 FPS per inch.

This is actually close to what I guessed from modern tests of loss per inch and figuring a little less than that per inch.

Gus

 

[Grumpa]

Just a thought, but by going from 2Fg to 3Fg, upping the charge or switching to, say, Swiss from GOEX, you might pick up that 130 fps.

 

[Zonie]

Years ago, Dixie Gunworks did the test your asking about but it was with a .40 caliber barrel.

They started with a 40" barrel and cut it down in 2 inch increments.

At each length, they tested 10 different powder loads and shot 5 strings to get an average velocity.

Just picking one of the loads at 65 grains under the patched roundball, here's what they got, starting at a 40" long barrel:

1987, 1992, 1994, 1966, 1913, 1932, 1903, 1838, 1784, 1733, 1703. The last one is with a 20 inch long barrel.

No. I don't know why some velocities went up.
I'm just reportin' what they printed. :grin:

 

[Artificer]

Just a thought, but by going from 2Fg to 3Fg, upping the charge or switching to, say, Swiss from GOEX, you might pick up that 130 fps.

Yes, of course you are correct. However, what I'm looking for is the differences in velocity per inch as the barrel is shortened, because that is going to have much to do with practical accuracy.

Gus

 

[Artificer]

No. I don't know why some velocities went up.
I'm just reportin' what they printed. :grin:

Jim,

Such minor discrepancies also show up when they cut modern barrels down one inch at a time. Thanks for the input.
Gus

 

[George]

However, what I'm looking for is the differences in velocity per inch as the barrel is shortened, because that is going to have much to do with practical accuracy.

I guess I don't follow your thinking, Gus. Wouldn't you think you could work up an accurate load at any stage along the way? Velocity can be adjusted by changing the powder charge, of course, so that within reason shortening the barrel doesn't mean the velocity has to decrease.

Spence

 

[Artificer]

However, what I'm looking for is the differences in velocity per inch as the barrel is shortened, because that is going to have much to do with practical accuracy.

I guess I don't follow your thinking, Gus. Wouldn't you think you could work up an accurate load at any stage along the way? Velocity can be adjusted by changing the powder charge, of course, so that within reason shortening the barrel doesn't mean the velocity has to decrease.

Spence

Spence,

Thanks for chiming in again.

Yes, you are correct for that train of thought, but that is not the direction I'm going with this information.

The "Auld Dictum" is that the longer 42-44" barrels in Long Rifles were supposedly more accurate and harder hitting than shorter barrels. For this to be demonstrably and noticeably true, there MUST have been a major difference in velocity between the lengths of barrels. Now, the only way to test that and rule out as many variables as possible, is to use the same barrel and load while one cuts the barrel shorter.

Taking the Rice Barrel Test and Plugging the average FPS of the shortest and longest length barrels with a 177 grain round ball, here are the differences we see at different ranges.

Yards / FPS / Energy / Drop in Inches
50 yds.
1082 460 -0.0
1140 511 -0.0
75 yds
992 387 -2.7
1029 416 -2.5
100 yds.
918 331 -8.1
950 355 -7.4
125 yds.
854 287 -16.6
882 306 -15.4
150 yds
797 250 -29.1
822 266 -27.1
175 yds
742 217 -46.2
767 231 -42.9
200 yds
690 187 -68.8
714 200 -63.7
225 yds
640 161 -97.6
663 173 -90.8
250 yds
593 138 -134.7
614 148 -125.4
275 yds
547 118 -181.5
567 126 -168.7
300 yds
504 100 -239.9
523 107 -223.0

OK, I worked quite some time trying to gather and put the information on this forum, so I will cut off this post and add more later, JUST so I don't lose the information.

Gus

 

[Artificer]

OK, to see JUST how much more accurate or harder hitting a longer barrel is with the SAME powder charge and ball, I plugged the information from Rice Barrels into the "Round Ball Ballistics Calculations for Muzzleloaders" found at in the following site and got the information above.
http://www.ctmuzzleloaders.com/ctml_experiments/rbballistics...

There is a difference between the two barrel lengths, to be sure, BUT just how much do they mean? I look at the results and I am afraid I just don't see enough difference that an 18th century person would have noticed between a 30" and 44" barrel.

Gus

 

[zimmerstutzen]

Results will differ with caliber. Between 45 and 50 calibers there is a definite loss of velocity. And it can only partially be made up for with increasing loads. A 54 or 58 does not follow the same graph lines.

 

[Artificer]

Results will differ with caliber. Between 45 and 50 calibers there is a definite loss of velocity. And it can only partially be made up for with increasing loads. A 54 or 58 does not follow the same graph lines.

I don't mean to be personally critical of you, but where are the results of a test that prove that? The .50 cal. ball came in at under 10 FPS difference per inch (average) with the black powder load.

Gus

 

[Artificer]

I am not saying that an increase in powder won't cause a bullet to travel faster, generally speaking. I am also not arguing that it takes less powder to propel a .45 cal. PRB faster than a .50 caliber. But these things are NOT a test of accuracy of barrel length differences between 30 inches and 44 inches.

The only way to test the accuracy and "power/energy" difference of lengths of a barrel is to use the same ball, patch and powder charge (as well as lube) and start with a long barrel and cut it down while recording the results.

Gus

 

[George]

The only way to test the accuracy difference of lengths of a barrel is to use the same ball, patch and powder charge (as well as lube) and start with a long barrel and cut it down while recording the results.

But comparing velocities as the barrel lengths change tells you nothing about accuracy. You have to shoot groups for that. I know nothing which links any particular velocity to accuracy, only the consistency of many shots at that velocity can show you that. Even that only shows you the potential, have to put it on paper to see if it translates.

Spence

 

[Artificer]

The only way to test the accuracy difference of lengths of a barrel is to use the same ball, patch and powder charge (as well as lube) and start with a long barrel and cut it down while recording the results.

But comparing velocities as the barrel lengths change tells you nothing about accuracy. You have to shoot groups for that. I know nothing which links any particular velocity to accuracy, only the consistency of many shots at that velocity can show you that. Even that only shows you the potential, have to put it on paper to see if it translates.

Spence

Higher Velocity gives a flatter trajectory and thus more practical accuracy, both for shooting at variable ranges without having guess as much on how much to hold off, plus the wind and other environmental factors don't have as much time to act negatively on the bullet. (I realize there is an upper limit on that for accuracy in each caliber and rifle, though.)

For the old claim that longer barrels "hit harder" than shorter barrels, there has to be a significant difference in velocity between barrel lengths and the only way to test that is by using the exact same load, in the same barrel, at different barrel lengths.

Gus

 

[zimmerstutzen]

Taking the example to the logical extreme, then a 7 inch pistol barrel would only be 250 fps less than a 32 inch barrel? Road apples!

 

[zimmerstutzen]

The additional fallacy with the rice test is that they only used 80 grains. Even in a 30 inch barrel they stayed under the load range of diminishing returns. Per the tests reported in the first ed Lyman book, they would not have seen diminishing returns in a 28 inch barrel until they exceeded 90 grains. The rice test parameters were predestined to give a false impression. They would have gotten similar results with 30 grains of powder. The results would have been different had they used 110 grains of powder, or had kept lopping off the barrel to 18 inches.

 

[Artificer]

The additional fallacy with the rice test is that they only used 80 grains. Even in a 30 inch barrel they stayed under the load range of diminishing returns. Per the tests reported in the first ed Lyman book, they would not have seen diminishing returns in a 28 inch barrel until they exceeded 90 grains. The rice test parameters were predestined to give a false impression. They would have gotten similar results with 30 grains of powder. The results would have been different had they used 110 grains of powder, or had kept lopping off the barrel to 18 inches.

I agree Rice may well have gotten a far different result in a 7" pistol barrel, but other factors would be involved with a barrel that short. The powder charge has to overcome the resistance of the PRB at rest and would not have much time/length for acceleration in a barrel that short. So a test like that would give a false impression.

Does the Lyman book give velocities per inch or per two inches from the same barrel with the same PRB and 90 grain powder charge over the range of at least 30 inches to 42 or 44 inches? Personally, I would bet that such differences would not be large both from the fact that modern barrels cut short don't show significant differences and their velocity is much higher - plus Plains Rifles gave accuracy as good or better than Long Rifle Barrels with PRB's and they were only around 33 to 36 inches.



Gus