I have been loading for my 7.62x39 for about 2 years with no problems. This last batch of loads had the primers backed out a little, about .008. I was using Win. and new Lapua brass WLR primers and a new lot od AA 2230. They were max loads of 29.5gr with 125gr Sierra .308 Pro Hunter. Loads were full length sized and crimped with the Lee FCD. I didn't have any problems with accuracy or signs of pressure. The only diff. I found was my vel. was down a bit from my previouis lot of powder.

I have read that this could be a headspace problem. What can I do to repair this situation?

Now don't go away, the gun is a Ruger Mini-30.

This is a typical excessive head space sign. The easiest way to avoid the problem is to back off your sizing die a little.

quote:

Originally posted by Zero Drift:
This is a typical excessive head space sign. The easiest way to avoid the problem is to back off your sizing die a little.

Works every time! this way you don't push the shoulder back as far and it will headspace properly. If that don't work just try neck sizing. Otherwise take it to a smith and have it headspaced.

that is good advise...

quote:

This is a typical excessive head space sign. The easiest way to avoid the problem is to back off your sizing die a little.

I set my die by raising the arm , screwing the die in to touch the shell holder then screw it down another 1/8 of a turn. When you say "back off a little" how much should back it off?

Thanks

Don't touch your die!! If you haven't had problems in the past you are probably just fine. The fact is you used "new brass" and full length sizing new brass will not change the dimensions at the shoulder. That new brass probably had a low spec dimension. It should now resize exactly the same as other brass you have been sizing because it is now fire-formed to your chamber. If primers aren't backing out of other once sized brass you've fired I'll bet a six pack these won't either. If you do alot of reloading treat your self to a stoney point headspace kit. They're resonable (about $35) and will help you set up dies to match chamber dimensions on your guns.

Kraky is right on! I formed some 7.7 Jap cases from 30/06 cases which is a easy and quite common thing. But when I fired the new formed cases the primers backed out a few thousands. I thought I had over pressured the case but realized that I was using the same powder load as the Norma cases I was shooting that day. Next round they fired perfect as they were formed to the chamber. And it beat paying the extreme price Norma charges for 7.7 cases

If you are really adventurous expand a couple of case necks to 8mm ID and bring them back down to 7.62 gradually until your bolt just closes.Now measure the distance between your die and the shell holder. See if there ie a difference between what you now find and what you were using before. You may need feeler gages or shim stock. The fact that it's a semi auto may make this a little more difficult but with a few smarts it can be done----RIGHT

Where am I? where was I? where do I want to be? Readjusting dies is no big thing, so don't be afraid to try somthing. roger

Well I guess the first thing we should have asked Steve was this all new brass or does the problem exist even with once fired brass. 7.62x39 is fired in mostly Auto’s or semi auto and the manufacture may have initially sized this brass where it would have no problem feeding and locking in Auto actions. Fire forming like others have suggested may solve the problem.

The primer backs out because the case is shorter than the chamber. Resizing cannot make the case longer. If the case is oiled lightly before firong it will came back and fill the chamber. The primers will not be protruding.At this point the resizer may be adjusted.
Good luck!

Hello the campfire:
Please excuse my ignorance, but why is primer back-out a sign of excess headspace?

The case should have moved back and reset the primer in the case if the pressure were not too low. This is not un-typical for a normal shot. The head of the case should impact the face of the bolt and not have enough space to allow a primer to back out even a few thousands, unless there is a problem with the bolt face. The shoulder should blow out to fit the chamber, as in a fireformed case.

I would suspect that the problem lies in the primer pocket itself being oversized or the primer being undersized, and the primer not seating well. Some of us have had these problems before particularly with progressive loaders. Firing the cartridge will pean the head a little and cause the primer pocket to fit better. I would suspect something like this, when this is the only case lot that the primers back out from.

Eliminate the simple reasons first (like plugging in the computer) before doing something drastic like re-head spacing the chamber.
Just my ingorant revings.

Judge Sharpe.

quote:

The shoulder should blow out to fit the chamber, as in a fireformed case.

Yes, and the case grips the chamber walls as it's fireformed and allows the primer to be pushed back until it reaches the bolt face.

Theoretically possible?... Yes. Likely?... I don't know... there's a lot of variables there, but checking the headspace would certainly rule one in or out.

Judge - What happens with excessive head space is the initial primer strike moves the case forward in the chamber. (Proper headspace with unbelted cartridges holds the case tight against the bolt face) As the firing pin continues its travel, it sets off the primer. The first reaction to the primer ignition is the primer backing out of the pocket as the powder ignites. The powder ignition holds the case in the chamber and maintains pressure against the primer so that the case does not move back against the primer to “re-seat†it in the primer pocket.

In many cases excessive head space leads to primer dimpling upon pin strike but not sufficiently to set off the primer. This leads some to concluded quite incorrectly that the primer was bad. The chances of finding a bad primer are extremely remote. The chances of finding more than one in the same batch are borderline impossible. If you find a “bad batch†of primers with a non-belted case and you are most likely experiencing excessive head space.

The case will stick in the chamber and stay forward until around 40KPSI or so. Then it comes back. That is why riveted primers also result from headspace.
Good Luck!

I have never experienced any head space problems with setting my die up with very light "cam over" on the press. then I set the ring down tight ion the die and use it that way every time. No problem in 20 years!

The only time I've had problems with primers backing out is when I use compressed loads. I always sit my cases on a flat surface after priming to make sure they are seated deeply enough so there is no wobble. Occaskonally after seating the bullet I'll notice a wobble when I again sit them on a flat surface. I can only conclude that the primer is forced back out a ways due to the compression forcing them out a ways. What do you think. Best wishes.

Cal - Montreal

Cal - Unless you have loose primer pockets, a compressed charge should not back out primers. Powder should not be forced into the flash hole to put any pressure on the primer.

Hello the Campfire:
Loose primer pockets in a batch of new brass sounds a lot more likely than a sudden headspace problem.
Judge Sharpe

Judge - If the case properly head spaces, the case base should be putting pressure on the bolt face when the case is chambered. Even with loose primer pockets, the primer should not be able to back out of the pocket due to bolt face pressure, i.e. - proper head space. This is why you seldom see belted cases with primers pushed out, even in the situation with loose primer pockets.

7.62x39 brass/ammo is sometimes short, as that insures good feeding in the semi-auto's it is usually loaded for. It is also a (relatively) low pressure round, so backed out primers may stay backed out through the firing process.

I had a batch of American Eagle (Federal) ammo do just that, and upon measuring shoulder dims, 50%+ were below SAMMI. They went back, and Federal sent me a check with an apology.

The fired cases were still short, as the low pressure didn't fully form the cases! Lots of other ammo has been through this same SKS without issue.