case forming 1st firing

[zwak 19]

dose anyone know how much of the pressure is used to form the brass to your chamber on the 1st firing or is it necessary to use brass that has been shot to check for pressure signs

 

[Rhovee]

Don't shoot for pressure signs on virgin brass. It will ruin some. You will get higher velocity before pressure on virgin brass. Mild charge for first firing. Then you can try.

 

[GLTaylor]

Firing higher pressure in virgin brass will deceive you. Part of the pressure is absorbed in forming the case. Next firing may be too hot!

 

[MagnumManiac]

Over a Pressure Trace II, the pressure difference between NEW and ONCE FIRED with IDENTICAL LOADS, runs between 5,000-8,000psi. This can climb sharply if the load used in the ONCE FIRED brass was at max pressure in the NEW brass.
The 2 are not generally interchangeable.

Cheers.

 

[FEENIX]

dose anyone know how much of the pressure is used to form the brass to your chamber on the 1st firing or is it necessary to use brass that has been shot to check for pressure signs

What are you actually fire-forming, for instance, .280 Rem to .280 AI?

 

[zwak 19]

What are you actually fire-forming, for instance, .280 Rem to .280 AI?

not changing size just new lapua 338 brass

 

[FEENIX]

not changing size just new lapua 338 brass

It might take a couple of full load firings for the brass to stabilize.