- Oct 4, 2003
- Reaction score
- Phoenix, AZ
A number of years ago, Dixie Gunworks did an experiment with a .40 caliber barrel to see what shortening it would do to the muzzle velocity.hadden west said:...On a long rifle, the ball is slowing down before it leaves the barrel. Something about the air pressure ahead of the ball, and the pressure behind the ball starts to equal out....
They started with a 40 inch long barrel and fired a number of different powder loads using DuPont 3Fg powder under a patched roundball. They recorded the muzzle velocity for each length and load.
With the lightest powder load of 38 grains they got the following:
40" barrel = 1551 fps avg
38" barrel = 1567 fps avg
36" barrel = 1543 fps avg
34" barrel = 1493 fps avg
Note that with the shorter 38 inch barrel the velocity was a bit higher than it was with the 40 inch barrel.
This tends to support that the barrel friction was slowing down the ball during that last 2 inches.
The 36" and all shorter barrels lost velocity when compared with the 38 inch barrel.
Going to the 47 grain and heavier powder charges, this slowing down because the powders gas pressure ran out of energy does not show up.
40" barrel = 1770 fps
38" barrel = 1747 fps
36" barrel = 1735 fps
34" barrel = 1610 fps