Thread: Projectile vs barrel length

But thats not how internal ballistics perform and the "engine driving the car to the end of the track" is the myth. With even the slowest powder the effect the burn has on the projectile is dropping rapidly after just a few inches of projectile travel down the barrel. The push the projectile has received has it accelerating to the end of the barrel but the rate of acceleration is decreasing.
The best velocity will come from the flattest pressure curve which will be from the slowest burning powder that is suitable for the particular bullet weight, irrespective of barrel length. Any powder still burning after the first few inches of projectile travel will not be enough to effect the rapidly dropping chamber pressure and have no real influence on muzzle velocity. Think of it as if the chamber was a balloon, the powder ignites and inflates the balloon which sends the projectile accelerating down the barrel. A fast powder will inflate the the balloon to its maximum( say 60.000 psi) but the burn is done and dusted so the balloon deflates rapidly. A slower powder will inflate the balloon to max but keep burning and hold the balloon at max pressure for a little longer and exposing the projectile to max presure for longer giving better acceleration
The key here is all of this takes place in the first part of the projectiles journey down the barrel so by the time its traveled a few inches its rates of acceleration are fixed.