Thread: Fire forming 270 to 280ai

Originally Posted by 7mm tragic

Sooo, I should be able to use a Lee die set designed for the "original ackley cartridge" and it will be fine for sizing brass in my saami spec chamber.

I have been able to determine the amount of shoulder set back needed by chambering my fired cases and comparing the difference between the ones that allow the bolt to close with no resistance vs the ones that don't.

Using this number I should be able to safely determine if my brass is indeed sized correctly?

Tell me if I'm missing something

If you have the dies then size a fired case and see if it bumps the shoulder back far enough to close the bolt

Originally Posted by 7mm tragic

Sooo, I should be able to use a Lee die set designed for the "original ackley cartridge" and it will be fine for sizing brass in my saami spec chamber.

I have been able to determine the amount of shoulder set back needed by chambering my fired cases and comparing the difference between the ones that allow the bolt to close with no resistance vs the ones that don't.

Using this number I should be able to safely determine if my brass is indeed sized correctly?

Tell me if I'm missing something

In simple terms yes that's what Iv found. EG: I have a proven traditional chamber from before the nosler SAAMI thing. Using Nosler and now Peterson SAAMI spec brass I find it dosn't stretch anywhere near .014 on fireing and I can resize it back to original size with redding improved 40 deg dies. I have seen some instances when the die is at the longer end of the spec and the chamber on the tighter end but it was only a few thou and the issue was solved by trimming the shell holder down a touch. Trimming the bottom of the die is also an option along with trying different shell holders.
You want to be bumping the shoulder no more than .002. I find a case that is firm on bolt close then size it a small amount, checking in the chamber and then screwing the die in no more than 1/16 of a turn each time untill it gives just a slight resistance then Ill measure it and bump a further .001-.002 from there. Best done with the firing pin removed.