Thread: Fast twist barrels

Originally Posted by Stocky

Not quite that assumes that all energy from burnt powder is instantly passed on to the projectile but realistically it has intertia and take time to accelerate similar to dropping a bullet from a high building. It doesn't instantly reach terminal velocity. Just because all the powder is burnt doesn't mean acceleration stops. The bullet will still accelerate until the force from the pressure of the xplosion is equal and opposite to the drag from the barrel and air. If you want to see this go run a few loads though quickload etc. Complete burn is not the same as max velocity. Ie why you will see 7mm08 and 6.5 creedmoors with 30 inch barrels etc for target.

Spot on. The pressure curve keeps driving the bullet faster until it runs out of puff. Area under the pressure curve over time vs resistance. Combustion doesn't drop to zero the moment combustion finishes.