Barrel Length vs velocity

[wszumera]

I was readin the "Gunsmith of Grenville County" and he seems to be sayin' that barrel length over 24-26" is overkill. I'm thinkin that is smokeless thought.

Can anyone point me to a thread where someone plotted barrel length vs velocity?

Thanks,

Clutch

 

[gmww]

I don't recall a thread off hand but check out Lymans 2nd Ed. on Black powder and muzzle loading. They have a load data with different length barrel and powder combinations.

:hatsoff:

 

[gmww]

Well I took out the old Lyman Book and here are some examples of velocities based on barrel length. I'm going to use the data on a .490 RB with 70 grns of 2f Goex.

24" = 1450 fps at barrel 1:48" twist
28" = 1471 fps at barrel 1:48" twist
32" = 1627 fps at barrel 1:60" twist

Hope this helps.

 

[JeffinNZ]

That does appear a slightly odd statement though it depends on the context.

If you are speaking in terms of velocity only then maybe. I had a 39 inch .40cal barrel on my cap gun, cut it down to 33 inches and velocities on on the lighter loads went up! Obviously the powder charges in the 20-30gr range were burning up way down inside the barrel and the additional travel was slowing them up due to friction.

In general I would rather have a longer tube to say 40 inches max for:

1) sight radius.
2) extra velocity
3) balance.

Horses for courses really.

J

 

[Zonie]

The Dixie Catalog has a section in the back that has a lot of information.
In one section, they present the 5 shot average velocity of a .40 caliber roundball with different loads. More to the point, they also repeated the test after they cut off the barrel.
The following is a list of velocities for a powder load of 56 grains of DuPont FFFg:
Length: Velocity: Increase
20: 1631
22: 1668: 37
24: 1710: 42
26: 1734: 24
28: 1742: 8
30: 1796: 54
32: 1819: 23
34: 1828: 9
36: 1836: 8
38: 1879: 43
40: 1884: 5

Why the large variation? I don't know. Maybe the printed data is in error. The 28 inch barrels increase of only 8 FPS looks suspicious and the 38 inch barrel suddenly got very efficient! :grin:
In general, it does appear that the velocity gains from a longer barrel seem to decrease as the barrel gets longer.
We should notice though, this data was obtained using FFFg powder which burns faster than FFg.
Because FFFg burns faster, it generates its maximum pressure very rapidly so I suspect the roundball is accelerated very rapidly at first but the rate of acceleration decreases rapidly as the increased volume of the bore becomes greater due to the length.
With FFg and its slower burn rate, the longer barrels may show a better velocity increase with the longer barrels? :hmm:

 

I'm building a rifle on a 52 1/2" long barrel by Ed Rayl in .50 caliber that I have been wondering about. It looks as though I am going to have to really pour the powder down this one to make 'er shoot according to what is being said here. :shocked2:

 

[paulvallandigham]

Th eDixie info doesn't say how many shots were fired at each barrel lengthto get these velocities. If the powder was not sifted prior to use, some of these charges may have been more 4Fg than 3Fg! The other variable that can change the velocities shot for shot is the changes in the thickness of the cloth patch, the lube used, and the actual diameter of the round ball. I found I could remove these factors by using an over powder wad to seal the gases, and not rely on the patch, lube or ball diameter to give me consistent pressure and velocity. So, I am not sure how really valid these tests were. You can always expect to see some variations in velocities due to the individual characteristics of any given barrel, how well it was cleaned etc. Even the percussion caps can deliver variations in velocity depending on how consistent they are made. But, when you see wide swings in velocities over a number of lengths of barrel, as we see here, you have to wonder about the data. Glad to have it, as you can learn some things of general use, but I don't think I am going to rely on this in detail. Better to use a chronograph to test my own guns, and loads.

 

[Zonie]

I posted the information because I though it had some bearing on the post and was interesting.

As for how many shots were fired, Dixie's data has a footnote which says "Velocity averages, expressed in feet per second, are for 5 shot strings..."

While I'm looking at it and typing, here is the numbers for a 75 grain FFFg load in the .40 caliber barrel:
Length, Velocity, change
20", 1818
22", 1844, 26
24", 1894, 50
26", 1902, 8
28", 1973, 71
30", 1984, 11
32", 2017, 33
34", 2063, 46
36", 2079, 16
38", 2099, 20
40", 2059, -40

Looking at this 75 grain load, which IMO is fairly "hot" for a .40 cal gun, it looks like the 56 grain load pooped out around 34 inches but the 75 grain load is still gaining velocity up to the 38 inch long barrel.

:grin:

 

[Zonie]

More stuff from Zonie:
Thinking there might have been a misspring or two over the years, I got out my 1980 catalog and the data seems to be the same.

I did notice something interesting though.
Comparing the 38 inch barrel with the 40 inch barrel for the different powder loads.
Many of the loads show a decrease in velocity with the longer barrel with the same powder charge.

The following lists the powder load and the gain/loss in velocity between the 38 inch barrel and the 40 inch barrel. A plus (+) indicates the 40 inch barrels velocity is faster. A minus (-) indicates the 40 inch barrel is slower.

GRAIN, CHANGE in feet/second
38, -16
47, +13
56, +5
65, -5
75, -40
84, -38
94, -46
104, +9
114, +78
120, +65

 

[paulvallandigham]

Don't you think that what is happening here is that the mass of the extra powder slows the travel of the ball down the barrel at the beginning, creating more compression and more complete burning of the powder with the heavier loads, than the middle loads? The reason I don't use these massive loads is that extra weight give more recoil out the back end of the gun, and all that extra velocity seems to disappear within the first 20-50 yds of range. I don't know if its my sensitivity to recoil, or barrel harmonics, or a combination of both, but most shooters shoot better groups at longer ranges with the ball leaving the barrel slower.

If you are shooting out to 60 yds, with a round ball gun set up for it, then by all means push all the powder you can get into the gun to shoot those Plus 2000 fps velocities and get that ball to the target before it has a chance to slow down. But, understand that a simple law of Physics says that what ever goes faster slows down faster. Once you get down to the trans sonic range( below 1400 fps., down to 1100 fps.) there are aerodynamic forces that begin to knock around those round balls, in flight, that open up the groups at longer ranges. We haven't figured out yet how to fool mother nature on this one.

 

[CoyoteJoe]

Dixie has been printing that same chart for many years now. Chronographs have improved a lot but there are still unexplainable phenomena which do crop up. When increasing loads in steps of five grains one may find that one increase actually reduced the velocity of the previous step but there may be a big jump at the next step. And perhaps that step which showed no gain may turn out to be the most accurate load, you never know. A one time test with one rifle just can not be applied as a "rule of thumb".
The first edition Lyman book shows a .50 caliber with 100 grains 3f producing 1875 fps from a 28" barrel, 1978 fps from a 32" length and 2095 fps from 43". Even with the 50 grain starting load the longer barrels show a gain in velocity and energy, though of course the gain is greater with more powder. Except for ease of transport, longer is better. Whether it is ENOUGH better to justify the bother is a personal choice.
How long a barrel would have to be before the friction started to REDUCE the velocity has been long debated but it is clear that such a barrel length would be well past four feet and even then only with very light loads. :grin:

 

[Zonie]

"... but most shooters shoot better groups at longer ranges with the ball leaving the barrel slower..."
___________________________________

Your comment reminds me of the day I decided to burn up some .45ACP rounds I had loaded 35 years ago.
These were loaded with the old crappy $5 Lee Loader and very light charges.
Anyway, I decided to just shoot them to see if they would even fire.

I was at an indoor range with two floodlights pointing downrange and set my target at 20 yards.

When the first shot went off, I thought I saw something. With the next shot, there it was again, the base of the bullet reflecting the light as it went down range.
I have no idea how slow they were going but I would guess somewhere around 600 FPS. I got to concentrating on how well I could see them as much as where I was aiming.

After firing all 50 rounds I noticed those slow bullets had eaten a 2 1/2 inch hole right in the center of the target! :shocked2:

Sorry for going off topic but I still get a chuckle out of that happening.