new brass question

[cervus]

Have 100 new lapua brass cases which Im using in a new 243 factory sako...

Are load testing at present for a hunting/varmint load.. Have only fired virgin brass in rifle. I notice Im getting the "odd" vigin case which when I chamber to fire, its hard to close the bolt. (comparable in feeling to say a fired case which is incorrectly sized).... After firing, these tight cases eject easily with not much effort,,,, feeling the same as the rest of the cases.

Bullets are all seated with a redding competition seater to be .040 off rifling. My new brass prep consists of... run case through expander mandrel to set seating tension at .002, trim cases, chamfer case mouth inside and out. Ream primer pocket plus flash hole.... load up.

So any ideas on why theres the odd new tight case plus Im assuming most people dont do any sizing of new cases???? I know years ago they used to run new brass through a f/l die to get dings out of case necks.....

 

[Mark M.]

Well, that odd case is why some people FL virgin brass.

 

[Mikecr]

Until new cases have been fire formed, you could have anything, and it means nothing.
And it doesn't matter if you intend to FL size or not. There are so many changes to cases on firing, which sizing can never undo, that nothing matters at all until fire forming has been completed.

I know folks try to make use of every brass firing. But IMO, until it's fully fire formed and stable, about the only use of it is for full seating testing. Then you can move into load development with it.
Why attempt anything else while brass is still changing?

 

[dok7mm]

Mikecr is right. Most likely you had some brass with longer base to datum length than those that chambered easily. As long as you can close the bolt, just fire them. I don't do load work-up until twice fired brass is ready to load. Second firing is mainly to find a seating depth and check velocities on a couple of powders. After two firings, the base to datum should be pretty consistent across your brass.

 

[bob4]

IMO, until it's fully fire formed and stable, about the only use of it is for full seating testing.

I've often wondered if seating depth test could be done while fire forming.

 

[Mikecr]

I've often wondered if seating depth test could be done while fire forming.

It's best to test seating while well away from a best powder node. This, so that you're not collapsing a powder node while changing seating results (2 big changes at once). Often, fire-forming produces a little less pressure due to energy given up to expand brass more in the chamber. And a fire-forming load is as likely different from your final developed load,, maybe not. But either way you can still find a best coarse seating setting here, to proceed with for further load development.
Might as well get as much as you can(that actually works) while fire-forming.