03-01-2019, 12:17 AM
On something that LR posted about powder burn. I fully agree the peak pressure does occur in the first 1.5 to 3 inches of bullet travel. There are a few things causing this to happen.
Powder burns most rapidly while under pressure and the higher the pressure the faster it burns.
The bullet goes from rest to in motion and has to over come being a static object, crimp if it is crimped and neck tension from the brass case. Then it meats possibly its most resistance the rifling where it is forced into the barrel and pressure engrave the rifling into the bullet.
That is a lot going on in a small fraction of a second The bullet still has pressure being applied to the base the full length of the barrel but after 3 or so inches the powder has expended almost all its energy in the for of very hot gases and as the bullet travels the chamber containing the gas is increasing rapidly as the bullet moves and the further it travels the larger the chamber is.
After the bullet has been engraved by the rifling it is just friction of moving down the barrel it is now sized to and picks speed up rapidly and pressure drops off rapidly but the bullet is still gaining momentum as long as the pressure behind the bullet is greater than the friction of the bullet in the bore the bullet will still be gaining speed which is why longer barrels produce higher velocities than shorter barrels in a short barrel there is less time under pressure because it does not have to ravel as far.
One thing about shorter barrels is they is more muzzle blast from one due to the gases being under higher pressure upon exit of the barrel than long barrels where the pressure has more time to reduce further as the bullet travels down the barrel.
Ever wonder why barrels wear out at the throat where it is not protected by brass, your hottest burning gases during firing the gun are located there under peak pressure while the bullet is being engraved. hottest gases and highest chamber pressure are exposed to the barrel at that location.
No I am not a ballistic engineer but actually wanted to be at one time. Just did not take that route but I am an engineer and long time reloader for rifle, handgun and shotgun powder consumption wise cartridges from 32 acp to 50 BMG.
Powder burns most rapidly while under pressure and the higher the pressure the faster it burns.
The bullet goes from rest to in motion and has to over come being a static object, crimp if it is crimped and neck tension from the brass case. Then it meats possibly its most resistance the rifling where it is forced into the barrel and pressure engrave the rifling into the bullet.
That is a lot going on in a small fraction of a second The bullet still has pressure being applied to the base the full length of the barrel but after 3 or so inches the powder has expended almost all its energy in the for of very hot gases and as the bullet travels the chamber containing the gas is increasing rapidly as the bullet moves and the further it travels the larger the chamber is.
After the bullet has been engraved by the rifling it is just friction of moving down the barrel it is now sized to and picks speed up rapidly and pressure drops off rapidly but the bullet is still gaining momentum as long as the pressure behind the bullet is greater than the friction of the bullet in the bore the bullet will still be gaining speed which is why longer barrels produce higher velocities than shorter barrels in a short barrel there is less time under pressure because it does not have to ravel as far.
One thing about shorter barrels is they is more muzzle blast from one due to the gases being under higher pressure upon exit of the barrel than long barrels where the pressure has more time to reduce further as the bullet travels down the barrel.
Ever wonder why barrels wear out at the throat where it is not protected by brass, your hottest burning gases during firing the gun are located there under peak pressure while the bullet is being engraved. hottest gases and highest chamber pressure are exposed to the barrel at that location.
No I am not a ballistic engineer but actually wanted to be at one time. Just did not take that route but I am an engineer and long time reloader for rifle, handgun and shotgun powder consumption wise cartridges from 32 acp to 50 BMG.