Primers backing out help

[Howfar]

Just picked up a 700 PSS in .308. Noticed on about half of the
thirty or so rounds fired, some of the primers had backed out
about 3-5 thousands. I use a headspace case gauge to resize
and had a light load of 41 grs of H4895 with a 168 sierra, FC
case,gm210m primer. No ejector marks, etc to show high pressure.
Need someones expertise as to if this is a problem or not to
worry.
Thanks

 

[Forum Boss]

Sounds like loose primer pockets. Not an uncommon problem with Federal brass after 2-3 firings. Suggest you get some Lapua or IMI brass. The other thought is that your load went haywire somehow--were you weighing the load for each case?

 

[Asa_Yam]

Might be soft brass, might be incorrect headspacing. Speaking of which, what type of headspace gauge are you using? A Wilson type gauge measures headspace against a SAAMI standard chamber. Works great, unless your chamber is larger than SAAMI. Not that uncommon, actually.

A gauge like the RCBS Precision Mic or the Stoney Point allows you to measure headspace against your chamber. Even if your chamber is longer than SAAMI, you can still use the measurements to ensure your reloads are still safe.

You mentioned "light" loads. 41 Grains of H4895 isn't light - it's nearly a full power charge. A "light" load would be under 39 grains. When charges are reduced, it is common for primers to protrude. This is because on ignition, pressures inside the primer pocket are over 9,000 PSI - a lot more than the pressure needed to seat said primer. Pressure from burning powder causes shoulder and case body deformation. This causes the case to move rearwards enough to reseat the primer flush with the head of the case.

 

[Howfar]

Weigh each charge on electronic scales. Use a Wilson headspace
gauge also. Will try another brand of brass to see if that
cures the problem. Never had this happen before in any PSS.

Is it a problem or can one live with it?

Thanks

 

[Asa_Yam]

I don't think that slightly excessive headspace is a problem, assuming that the cause is a longer than spec chamber. Excessive headspace as a result of receiver or bolt lug setback is a BIG problem - it means the metal in these parts has permanently deformed.

Factory brass is often shorter than SAAMI minimum chamber spec, and most chambers are typically longer than SAAMI minimum chamber spec. Between the two, I can see where you could get more than .005" difference between new and fired cases.

 

[harrys]

question is were the primer pockets clean before they were loaded ?????