The Firing Line Forums - View Single Post

Bart B. · December 26, 2012, 03:34 PM

Slamfire, that's a good looking chart on pressure, distance and time for a 7.62 round's bullet in the barrel. It stops at 22 inches so was it based on a 24 inch barrel and the bullet starting out with a 2 inch head start in the case?

Also, where did it come from?

My only issue with it is where the bullet's movement starts. MIL SPEC release force for 7.62 NATO bullet's between 40 to 60 pounds of force. At about 530 to 800 psi of pressure in the case producing that force on the back of the bullet, it'll start to move out of the case neck. Then several more pounds or so of force to push it fully into the rifling. Whereas the chart shows the bullet doesn't start moving until there's about 8000 psi (596 pounds of force).

This is an area of internal ballistics I'm not totally understanding based on my knowledge of physics. But the following helps:

http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA431357

December 26, 2012, 03:34 PM	#14
Bart B. Senior Member Join Date: February 15, 2009 Posts: 8,927	Slamfire, that's a good looking chart on pressure, distance and time for a 7.62 round's bullet in the barrel. It stops at 22 inches so was it based on a 24 inch barrel and the bullet starting out with a 2 inch head start in the case? Also, where did it come from? My only issue with it is where the bullet's movement starts. MIL SPEC release force for 7.62 NATO bullet's between 40 to 60 pounds of force. At about 530 to 800 psi of pressure in the case producing that force on the back of the bullet, it'll start to move out of the case neck. Then several more pounds or so of force to push it fully into the rifling. Whereas the chart shows the bullet doesn't start moving until there's about 8000 psi (596 pounds of force). This is an area of internal ballistics I'm not totally understanding based on my knowledge of physics. But the following helps: http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA431357 Last edited by Bart B.; December 26, 2012 at 03:48 PM.