Primers backing out

[DaveInSoCal]

When I returned from the range I found that the primers in the cases that I fired in my 30-06 Ruger MK11 Stainless are all backed out .003 to .006. Loads were 47 to 49 gr IMR 4895 with 150 Hornady's in Win & Rem cases, which should be fine.  I will admit that a .308 round was accidently fired in this rifle and it made a bit louder boom and slightly more recoil. Suspecting a headspace issue, I checked with NO and NOGO guages but all was well. I can't figure it out and am hoping you guys can give me some help. All thoughts are appreciated. Thanks Much.

[gunnut69]

Primers backing out are usually a sign of light loads and/or head space issues. They indicate a head space condition existed when the round fired. I would test fire a couple of factory rounds and check if they to exhibit the high primer condition. I'll bet they don't.  Firing a 308 in a 30-06 while not good should not produce a high pressure situation. They contrary is the likely scenario. The oversize chamber should lower the pressure the round would have created. Don't have my books handy but are those light loads? That may be the culprit.

[DaveInSoCal]

Thanks gunnut69, but Lyman says start load is 46 grs and 51.5 max with 150's using Win cases. My loads were 47 to 49 (with most being 49) and I was using Win & Rem cases. I will try some factory ammo as you suggest, but I don't see how my loads could be low pressure. Any other thoughts?

[John Traveler]

Your loads are in the "moderate" range, and should produce normal .30-06 pressures.

Years ago, when the US Military adopted the 7.62 NATO round for it's service rifles and machine guns, there was some concern over safety issues if a 7.62 NATO round (.308 Winchester) was inadvertently fired in a .30-06 rifle.  Extensive testing proved that there was no hazard to to the shooter or the rifle.  The .308 round is wide enough at the shoulder to wedge up in the .30-06 chamber to seal and prevent gas blowback.  Similarly, it was determined that even with extensive firing with such an ammo/rifle mismatch, there was no gun damage.

There is a remote possibility that your FL sizing die and shell holder are mismatched, giving you a CARTRIDGE excess headspace problem.  Remember that excess headspace can be caused by out-of-spec ammunition OR an out-of-spec chamber/bolt relationship.

I second gunut's advice to fire factory loaded cartridges and check again.

HTH
John and

[DaveInSoCal]

Thanks John, that was good info. You guys are great.

[gunnut69]

Thanks John I always forget to clarify when I mention head space. Head space is a condition of mismatch between a cartridge and the chamber it's fired in. This may be because of problems in the cartridge's dimensions or the chamber's dimensions or both!! Over sizing of cases is unusual but a specific combination of the dimensions of the shell holder and the sizing die can produce the situation.

[wtroger]

All non crimped primers back out some when fired the case usually expands and comes back and reseats the primer you said the headspace was ok. I would say to check the case length after resizing shoulder to base and compare that to a factory round or the go-gauge or a technical drawing founf in the loading manuals.

[trotterlg]

I would size a case and then put a layer of masking tape on the head and see if you can still close the bolt on it, then try two layers, normally the primer is blown back, then the case is pushed back over the extended primer leaving it flat with the case head.  One layer of masking tape is about max for head space. You may also want to take a look at the bolt head and make sure it isn't caving in around the fireing pin.   You can also check head space by loading a sized primed case with no bullet and no powder and firing the primer, the primer will back out against the bolt head and you can measure the exact head space you have with that size case by how high the primer is above the case head.  Larry

[tomzuki]

How many times has the case been re-loaded??  I believe the primer pocket will wear each time, leading to the pocket growing and becoming out of spec.  It should show up on how the primers seat, being very easy requiring lighter pressure........