Primer flattening

[thekubiaks]

I am fireforming new brass (6.5 x 284 Lapua and Rem 7mmSTW) I am shooting what the manuals tell me is a moderate load. I am seeing a little bit of primer flattening on both cartridges. The 7mmSTW flattening is a little more noticeable than the 6.5 x 284.

The question is, since I am fireforming and the cartridge is expanding to the chamber, is there a little headspace "slop" that is allowing the rear of the cartridge to slam into the bolt face and flatten the primer?? I don't get any sticky bolt handles after firing. I plan to go back to the range with the fireformed brass and see if it will do it again but am I missing something?? Thanks for the replies.

 

[Fireball Fred]

too many variables

the brass you stated is made to sammi dimensions for these cartridges. fireforming is only needed for wildcat cartridges. ie: making another cartridge from a base cartridge. without knowing your primer seating procedures, load recipes, and chamber dimensions one would may be passing missinformation on the web. all of the above could cause flattened primers, improper seating, too much fast burning powder, bullet seating, or overdimension chambers. also if bullets are seated touching the rifling, even a moderate charge could cause a spike in pressures. the only rational advice one could give you with the data you provided is, yes flattened primers is an indicator of something wrong. Greg Moyer

 

[marion packett]

I have a custom chamber 6.5-284 Hoover. I fireform with 47grs of H4350 behind the Sie 142. The shoulder will advance .005-.006 " Then I can shoot 48-48.5 grs. But if I fireform with 47.5 grs, particularly on a warm day, I'll blow primers. There's a lot of stretching going on when ff. My head spacing is btween .000 and .001

 

[rooshooter]

If your barrel was chambered a little deep, then, yes your cases could be slamming back that .005-.006" with factory brass. Are you jamming the bullets hard into the lands with enough neck tension to hold the case against the bolt head when the firing pin hits it?
Have you measured if the case head is expanding after firing? The Lapua 6.5x284 brass is not as hard as the Winchester brass and if the presuure is high, then the case will expand back at the case head, telling you that the pressure is getting high. If you get more than .0005" (half a thou) expansion, then pressure is up there.