c11man wrote:
are you sure that a 20ft barrel is worth it? unless you are shooting a very heavy projectile the last 5ft might now do much good
I clocked some projectiles in the barrel on some barrels up to 10 feet in length. I saw first hand where the maximum flow for a barrel was achieved and additional length added no acceleration. The added length only added more drag on the air flow. In a 10 foot 2.5 inch barrel max velocity was reached in about 6 feet. Cutting off 3 feet reduced the amount of air the projectile plowed. As a result the projectile continued acceleration all the way to the muzzle. This resulted in a higher muzzle velocity than the longer barrel.
Longer is not always better. Here is a scope trace showing the times a projectile passed pick-up sensors on a barrel 10 feet long. Only the last coils are shown. By checking the distance between blips, you can see that there is very little to no acceleration as the projectile passed these last coils. The very last coil on the muzzle has inverted polarity as a marker.
PM me if you would like to re-create this experiment and record your own barrel trim performance. Procedure is posted on-line.
