Primers Backing Out

flyingtorpedo

My load: 8mm mauser, 42.5 gr of IMR 4064, 170 gr bullet to 2.850 OAL, twice fired Remington cases, neck sized only with my collet die-I only have one 8mm.

I'm back with another question with my 8mm mauser reloads. I've been working my way up to the JS data in my Lyman 48th from the wimpy loads in my Lee manual. The load I was using is 1.0 gr lower than the starting JS load in my Lyman, and the highest pressure the cases have seen. All of my primers were below flush, I checked twice before I put them in the box and again at the range after my first primer backed out. Only about half of my primers back out. The others were still below flush or flush, and none were flattened. The one that backed out the most was ~.017" above the case head. Most of the ones that backed out are just above flush. There was the same amount of resistance when I primed them with my Lee auto prime as there was the previous time. There is no crattering and no evidence of gas leaks around my primers or bolt face. The cases extracted normally. So what's going on? The accuracy was much better than my previous loads but I quit because of the primers. I have some left, and I wasn't planning on that.[:(] Thanks for the help, again.

I was going to post a pic but I can't get a decent one-I'm photographly challanged![:D]

Tailgunner1954

Backed out primers is a sign of LOW pressure. Your .017 measurement indicates (to me) that your pushing the shoulder back to much during sizing (that or you've pounded them back by using them at such a low pressure on previous firings).

As a side note, Nosler runs 4064 from 43.0 to 47.0gr under a 180gr bullet. I'd expect the data for a lighter bullet to be even higher than that. IE: Speer #13 shows 45.0 to 49.0gr of 4064 under a 170gr bullet.

perry shooter

Primers and ammo can react in ways that at first glance boggle the mind.. The first time I worked on a colt single action I wanted to test for function it was very cold outside so I just loaded empty cases with primers and shot in my den "with wife out shopping" one Bang and then the pistol was LOCKED UP primer backed out and cylinder would not turn[:(!][xx(][V][:(][?]. I had a BIG learning curve . in firing a cartridge the pressure needs to be enough to expand the case to grip the chamber walls but it also must have enough pressure left to push the case back to press against the bolt or breach face . If you have a rough chamber or if you have light pressure the case may not press against the bolt face and if the shoulder is set back then the primer will back out of the primer pocket . . I suspect you have the case too short for the chamber.

flyingtorpedo

I'll try some new cases and see what happens. I guess I'll pull a few bullets tomorrow. Thanks for the help.

v35

I believe you are bumping case shoulders back too far creating excess headspace.
With your firing pin and spring assembly removed from the bolt, try a sized case in the chamber. You don't want to feel any forward and aft play in the bolt handle.