Case sizing new brass

[MVW]

I have read many articles on case prep, but one thing that still perplexes me is proper case sizing prior to neck turning new brass. I thought I might clean up the necks on some new Lapua 223 cases - just a tad off. Though I pose the question for 223 it is not specific to the 223 - I have noticed the same thing with 308 brass.

Based on measurements from many fired cases in my gun, the head space is roughly a SAAMI spec chamber (headspace=~0.000" or perhaps 0.0005 shorter). The new brass headspace seems to be anywhere from 0.001 - 0.004 shorter than SAAMI. To get them all to the same headspace, some are going to get bumped back a bit. Then when I fire them, they will all need to stretch. Is 0.004 - 0.005" stretch on new brass excessive?

Thanks, Mike

 

[bigedp51]

I have seen cases .011 shorter than minimum headspace, meaning when manufactured the cases were far shorter than SAAMI manufacturing standards.

On my .223 cases I seated my bullets long and jammed them hard into the rifling for fireforming.

I did not turn my necks until after they were at least fired once and formed to the chamber and had the shoulder pushed forward. I did not see any accuracy improvement by turning necks in a standard factory chamber on my Stevens 200 .223 26 inch HBAR.