Lapua brass Headspacing?

[TrxR]

Ive got a F/TR 308 here and was wondering when I should start worrying about sizing the body? Ive got some once fired Lapua cases from this rifle. Would they already be fully formed to the chamber. Would this be the dimension I should try and keep them at from now on out? Or should they be fired a time or two more?

My Fired brass is averaging between 1.624 to 1.625 and the Vrigin brass same lot is between 1.620 and 1.621.

Thanks

 

[Dusty Stevens]

You should be full length sizing on every firing for consistency and to make sure your rifle functions when youre on the line. Brass is not fully formed until about 3 firings on such as a 308 but you can start load development after the first firing

 

[mikecr]

Would they already be fully formed to the chamber

Think about it,, how would anyone but you know that?
One standard in setting bump is to remove the striking spring and feel resistive bolt turn on a chambered round. I would pull a plunger ejector for this testing as well. A bump of 1thou, or 2thou (at most) from slight resistance should provide needed headspacing. This of course has to be measured, each and every one, every time, to produce consistent ammo.
Don't assume ammo is headspacing the same, and don't assume FL sizing is actually making ammo consistent.

 

[TrxR]

You should be full length sizing on every firing for consistency and to make sure your rifle functions when youre on the line. Brass is not fully formed until about 3 firings on such as a 308 but you can start load development after the first firing

I was foolish enough to work up a good load on Virgin brass. Should I expect much difference with once fired ? Im now thinking a slight powder change might be needed but my seating depth should be fine.

 

[Dusty Stevens]

I was foolish enough to work up a good load on Virgin brass. Should I expect much difference with once fired ? Im now thinking a slight powder change might be needed but my seating depth should be fine.

Itll be close enough the atmospheric change on the next day will probably do more. Tweak that powder man.

 

[Bart B.]

My Fired brass is averaging between 1.624 to 1.625 and the Vrigin brass same lot is between 1.620 and 1.621.

To me, that's a sign of a reduced load not expanding the case to fill a chamber with 1,630" headspace. Your chamber headspace may be less.

Most new 308 brass is minimum 1.627" headspace. I think your cases might be shortened by firing pin impact and not expanded to fill the chamber space.

What load are you using?

Case headspace 1 to 2 thousandths less than chamber headspace is fine. Good enough for dozens of reloads per case and match winning record setting results.

 

[TrxR]

My loads were 44 and 43 grains of Varget behind 185 Juggrenaughts, Using CCI BR2 primers with 5 thou jump.

 

[TrxR]

My velocities at 43 Average 2750 out of a 30 inch barrel. Length with Hornady comparator is 2.267 lands at 2.272

I rechecked all 65 of my first fired brass and they range from 1.6235 to 1.627

and my new unfired brass is from 1.619 to 1.621. Im thinking the ones that stretched the most were the ones at 44 grain .

So Im thinking a couple more firings and keeping an eye on them for sticky bolt before I start sizing the body.

 

[riflewoman]

You’re fine. If your rifle is at 1.630 your brass will be less than that always. There is some springback unless your loads are way too hot.

As for tweaking the load you developed this is where a good chronograph can yell you lots. But you need to have more than 5 shots to get good numbers. 15 shots will tell you a lot more about your consistency that three 5 shot strings ever will.