Primers backing out

[JudgeBAC]

Primers backing out is usually caused by too much pressure. It seems I am having the opposite problem. While shooting the RCBS 180FN weighing in at 194 gr. in a Marlin 336 CS 30-30 with 29.7 gr. of MRP the primers have backed out a smidgen. I had the same problem with a .303 British today Lyman 314299GC 16 gr of 2400 and 20 gr. of XMP 5744. These loads are no where near max and should not cause pressure problems. What gives?

[jtaylor1960]

Sometimes a little extra headspace will cause primers to back out even when pressures are quite safe.You often see this with factory ammo as it is made to fit even the smallest chamber.You can try sizing your cases so that they headspace on the shoulder and not the rim.Good luck.

[44man]

Very low pressure loads will not let the brass move back to the bolt and primers will back out. You can see this if you shoot rubber or plastic bullets in a revolver with just a primer, no powder. Cases used for rubber bullets need the flash hole drilled out larger.
Primers do not back out with high pressure, they just flatten.

[mag_01]

Same as 44 Man Pressure may be to low --- Mag

[45 2.1]

Headspace is the issue here.

[454PB]

I adjust all my bottle neck dies to headspace on the shoulder, including all my belted magnums. I agree with the others....you have some excess headspace.

[fourarmed]

This has been discussed here before, and if you do some searching, you will find more info. Even if you jump through hoops to push the case shoulders forward, they will eventually be set back again. Some members have successfully enlarged the flash holes on cases used for very light loads. In my experience, if you are careful never to load your light-load cases with anything else, they will last a long time.

[Wayne Smith]

Primers always 'back out' when the cartridge fires. This is so universal and constant that John Garand designed an automatic rifle action around it. The cartridge case expands and slams back against the bolt face, re-seating the primer, in all normal loads.

44man is apparently right, your loads are light enough that there is not enough r4ecoil to re-seat the primer when the cartridge case comes back against the bolt face.

[MtGun44]

Measure the amount they are protruding. This is your
effective headspace. Is this a rimmed or rimless case?

You might possibly get some setting back of the shoulder of
the case due to the firing pin strike, especially in a small
case and a heavy firing pin system, at least theoretically.
I don't know if it is actually possible. If no case 'resizing'
is happening (and it can't with a rimmed case) then the
protrusion you measure is your headspace. Should be
a pretty small number of thousandths, like under 10.

Very light loads in my 1902 7x57 Remington Rolling Block
gives backed out primers, but I KNOW that all these rifles
have "excessive" (generous) headspace from the factory by
modern standards. Never blows a new case, but the stretch
is large enough to limit reloading to about three uses, I junk
the brass after third shot.

Bill

[joeb33050]

Primers backing out is usually caused by too much pressure. It seems I am having the opposite problem. While shooting the RCBS 180FN weighing in at 194 gr. in a Marlin 336 CS 30-30 with 29.7 gr. of MRP the primers have backed out a smidgen. I had the same problem with a .303 British today Lyman 314299GC 16 gr of 2400 and 20 gr. of XMP 5744. These loads are no where near max and should not cause pressure problems. What gives?

I've read the replies and here's mine.
First, if the primers are backing out just a little, say .010" or under, then there's no problem with your loads. Just keep on shooting. There's no need to drill larger flash holes, this is the solution in cases that headspace on the neck, doesn't have anything to do with rim headspacing cases.
Second, you can keep the primers from backing out by headspacing on the neck. Only neck size these cases and they'll headspace on the neck, fit the gun, and may be used for any safe load.
Third, bolt heads adjusting headspace are available for the Enfield, if needed.
Fourth, you can and I would check headspace using paper shims on the bolt face. Mike the paper, put in paper or aluminum foil or saran wrap or ? shims, on the bolt face-until the bolt meets resistance. Measure the shim stack; if it is over .008" or maybe .010" I'd have the gun looked at.
Another way to check headspace is to just seat a primer in a case, put it in the gun, close the door, open and take it out and measure the primer protrusion. Primer protrusion plus rim thickness = headspace. Again, over ~.010" and I'd have it looked at.
Fifth, you can adjust the case headspace by peening the rim edge forward. This works and well for SS cases when headspace is way too much, but is a bit difficult. I've fiddled with this, it works just fine for a few cases used breech seating and loading singly.
Go back to first, you probably don't have a problem.
joe brennan

[Bob S]

I have several "lots" of fifty Den 42 cases each in old MTM boxes that have been fired over 40 times with my old go-to load for the 03A3 of 40 grains WW II surplus 4831, Lyman/Ideal 311284 and Rem 9-1/2 primers. The primers always backed out. I used to "partially resize" these by backing the FL die out a half turn. With "ordinary" loads (of "normal" pressure for the 30-06), this would push the shoulder forward and cause chambering difficulties. With these very low pressure loads, I'm not certain if it pushed the shoulder forward or not, but the cases have continued to function quite well; the primers continue to "back out" the same amount with each loading, and there have been no signs of head separations. About 20 years ago, I sectioned one case after all 40 numbers in the MTM label had been "X"'d off or blacked out, and there was no sign of thinning above the head, or any other problems. So I don't loose any sleep over it.

(For any youngsters here, the labels that MTM gave with there 50-round boxes used to have the numbers 1-40 on the bottom, so you could keep track of how many times a "lot" of cases have been reloaded. I notice that sometime in the past 25 years or so, the labels have been changed so that they only have 1-10 on the bottom. I guess the newbies can't figure out how to maximize case life beyond ten loadings. :mrgreen: )

Resp'y,
Bob S.

P.S. Hi Joe!

[44man]

I would not drill flasholes either, I only do that for the rubber boolits in the revolver and those cases are kept separate.
The best way to form the brass is to shoot a hotter load the first time then neck size only. If the case is hard to chamber, then adjust the die down ever so slightly to move the shoulder back some and try them for fit again. The lever gun doesn't have any power to chamber a case if it is too long but once the right amount of sizing is found they go right in. No need to run them all the way into a die as long as they work.
An easy way to check headspace is with masking tape (Not the cheap paper thin crap.) Put a piece on the head of the case and trim it around with scissors, chamber it. At 2 pieces there should be resistance and the gun should not close with 3 pieces.
A little more headspace doesn't hurt anything, just fit the brass and don't size it all the way down. Cases will then last as long as in any other gun.
Two of the worst guns to load for are the Remington pump and auto, some need a small base die or fired cases won't chamber at all.
Then too, the primers backing out a little is no concern with the light loads, stop worrying. [smilie=1:At least you know the brass is not being over worked.

[JudgeBAC]

OK, thanks for all the great information. I measured the primers and they backed out about .005-.006 for both the 30-30 and .303 so based on what I read, I shouldnt worry about this. I still have some neck tension issues especially with the .30-.30 but a Lee Factory crimp die ought to solve this with the .30-.30.

[fourarmed]

IIRC, the last time this came up, one of the members did some testing and found that it was the blast from the primer that actually shortened the case, not the firing pin strike.

[MtGun44]

With only 5 or 6 thousandths headspace, and rimmed cases you are in
great shape. Cases will probably last forever.

Bill

[44man]

I can't see that at all! :roll: With below max loads, all cases shorten as they swell to the chamber walls unless the chamber is minimum as in a bench gun. The larger the chamber, the shorter the brass gets.
With excess headspace, the firing pin can move the case foreward but the brass will expand back to the bolt unless a very light load is used. Heavy loads stretches the case web and if the brass is full length sized all the time, life is short for it. With low pressure, the primer will move out and stop at the bolt and if there is not enough pressure to expand the brass back, the case will stay short. It has also shortened from expanding to the chamber walls so it might be a lot shorter then a new case fired with a hot load.
Neither the firing pin strike or the primer blast will shorten brass. Nothing will shorten brass except the expansion to the chamber walls.

[Bob S]

Firing primers only in a rimless case WILL push the shoulder back a small amount, and there is (obviously) no radial expansion of the case.

Resp'y,
Bob S.

[Char-Gar]

Well when this "tech talk" starts I usualy stay out of it, because of my general state of ignorance. But... this time I will jump in a mite. The "theory" has been that with very light loads cases can shorten and in time ignition will become iffy. Whether that shortening at the shoulder is causes by the primer or firing pin blow really doesn't matter. That is the theory that has been around for years.

Now, to fact and what I do know. I fire formed a lot of LCNM brass in my 03A3 chamber and drilled out the flash holes. I loads these cases with 18/2400 over the bullet of choice. I can detect no difference in accuracy or pressure. If the theory is correct, then these cases should never shorten.

There is a question about whether 18/2400 is light enough to cause case shortening in the first place, but that is another issue.

You would not want to use cases with drilled flash holes for full snort loads.

[MtGun44]

I believe that the case at hand is neck sized, rimmed cases
with light loads. In that application, I would bet on very
long case life. I don't think that primer can push the shoulder
around on a rimmed case, and if you are neck sizing, the
body will just operate in the elastic range for all but the first
shot. I expect you may need to anneal the neck after
some number of reloads, but even that will depend on the
chamber neck size as compared to the sizer die. Brass does
work harden, but not when operating in the elastic zone,
so only the necks will work harden in this case, - pun intended. :-D

For rimless cases, or full length sizing, or heavy loads -- it will
almost certainly be very different.

Bill

[Bob S]

I don't think that primer can push the shoulder around on a rimmed case, ........
For rimless cases, or full length sizing, or heavy loads -- it will
almost certainly be very different.

Bill

Agreed! :-D

Resp'y,
Bob S.

[MtGun44]

Then, sir, we are in clear agreement!

Well done. :drinks:

Bill

[fourarmed]

I have seen the same problem in a Wichita 7mm Int-R, so it can happen with rimmed cases, too. Excessive headspace is not limited to rimless chambers.

[MtGun44]

Absolutely correct. My very old .38-55 Win 94 has a slightly large
headspace, too. Rimmed chambers can have excessive headspace,
of course.

The thrust of a primer firing or the firing pin blow can't push the
shoulder back on a rimmed case, because the rim takes the load.
The shoulder takes these loads in a rimless case, so it may
shorten the case.

Bill