Head space on new rifle

[swampbug]

No problem. The other thing that's confusing is that new brass can actually grow if you full length resize too soon. The die will squeeze the bottom of the case and that will force the shoulder forward into the excess space.
You should also not set your trim length until you are sure your brass has been fully fire formed to your chamber.

 

[Mickp7]

No problem. The other thing that's confusing is that new brass can actually grow if you full length resize too soon. The die will squeeze the bottom of the case and that will force the shoulder forward into the excess space.
You should also not set your trim length until you are sure your brass has been fully fire formed to your chamber.

Hmmm...So you are saying to use only neck dies?

I've been FL sizing each firing, but not pushing the shoulder back. I have also been trimming to the specified length each firing. It's only been .001 to .003 each trimming, but I get my inside and outside chamfers at the same time (Henderson).

I do check that they are chambering easily as I size.

I'm about to start more cartridges so I'd like to do this right!

 

[swampbug]

No to just neck dies. You're doing it correctly. Most people use a full length die with a neck bushing in it. They set it up to just touch the shoulder but then back it off a little to allow the brass to fully form. And it still gets neck sized.
The full length die also sizes the base of the case which is necessary even if you back it off for shoulder growth. The Hendersons are great. I wait on trimming until the brass is fully formed just to avoid over trimming.

 

[ARlife4me]

I'm tagging in on this 1!

What could be my issue is on AR's with short mags and new brass? I've always fl sized in AR's to not have out of battery issues/not fully charging.

 

[Mickp7]

No to just neck dies. You're doing it correctly. Most people use a full length die with a neck bushing in it. They set it up to just touch the shoulder but then back it off a little to allow the brass to fully form. And it still gets neck sized.
The full length die also sizes the base of the case which is necessary even if you back it off for shoulder growth. The Hendersons are great. I wait on trimming until the brass is fully formed just to avoid over trimming.

Got it, thanks again and glad to hear I'm on the right track.

The cartridge I currently load for is the 300 PRC. Trim length is specified at 2.570 in one manual and 2.565 in another. I've been going with the 2.570 so far.

 

[ARlife4me]

Got it, thanks again and glad to hear I'm on the right track.

The cartridge I currently load for is the 300 PRC. Trim length is specified at 2.570 in one manual and 2.565 in another. I've been going with the 2.570 so far.

With the prc line it seems to be .015 less, but I've trimmed the 6.5 @ 2.020". Wonder if it's about growth?

 

[cajun]

Always wait until the brass fully forms to your chamber and the bolt gets sticky. Then start measuring with your comparator.
You can use the comparator numbers, or the tape method, or remove your firing pin and ejector to take pressure off the brass and then chamber the brass. The bolt should easily drop half way.
If you are fire forming your brass, start with a low powder charge and jam the bullets. Jamming the bullets forces the case back against the bolt face so that any expansion is in the shoulder area forward. If you don't, you risk the case head area being expanded and pushed back against the bolt face which can lead to case head separation.

if your shooting new brass in a chamber and have a case head separation you've got problems. While jamming bullets and using light loads to fire form is a good practice it's not necessary if your chamber is in spec and your not making brass from a different caliber where you need to limit stretch. It's not a bad practice with belted mags as case stretch can be excessive on the first firing. however I've not done it and had cases stretch a good bit on the first firing and still last multiple loadings as long as you dont excessively bump the shoulder going forward.