M1 Garand gas plug removed for singles load development . Problem primers are backing out .010 - .012 " . Not all the time !. What could be wrong ??.


Yes I uniform my primer pockets . The primers backing out of the pockets happens with Commercial brass more so than with Military brass .

It still happens and it's erratic . so why if it was a head space problem , it doesn't do it every time ?.

Cartridge spaces on the shoulder all specs are good to go . Normal pressures nothing excessive 4895 middle of the road loads 2575- 2625 FPS .
Accurate arms 2495 does it to .
Now my other Garand doesn't do this ?. I've got a friend and his does it to !!!??. He had his checked for head space , it's fine according to the gun smith . Now he has several Garands and another one he has doesn't do it either !. We have yet to check the others .

I would sure like to find out why it's doing this . Hopefully a M 1 Gun Smith on the site will take a look at this . Thanks to every body who replies ... salute

I'll hazzard a guess that it's because your gas plug is out. Your venting too much gass out the open port, and the pressure falls off in the chamber before the brass casing can expand and seal the rear of the chamber. As to why some of your rifles do it, and some don't, I would put that to variations in barrels/gas ports/chambers, etc. No 2 rifles will ever be exactly the same.

Try shooting same rifle, same load, but put the gas plug back in. You can easily shoot singles with the gas port in, I used to do it all the time with all 3 of my Garands.

This is my theory.

Hello,

It is not clear to me why you are removing the gas plug to begin with???? Weapon was not designed to be fired in that manner, but perhaps I am missing something after some 40 plus years of shooting the Garand. I am sure you are familiar with a "sled" for single firing and perhaps you are trying to eliminate the stretching of brass due to the violent extraction operation as found in the Garand??

What Slowpoke Slim says!

Primers backing out is symptom of loww pressure loads, very common in cast bullet shooting. I believe your loads are on the edge on this pressure area, sometimes they do sometimes they don't. The fact that they are being used in a Garand, with or without gas plug is probably irrelevant. These cases are being shortened head to datum, they can become dangerous to later use with high pressure loads if they become too short.

Driver : Ditto !. As well as saving the Op rod .
Yes using a sled .
I could use the gas port as I have an adjustable one , but it still would operate the Op rod which is what I'm attempting to eliminate .

SlowPoke Slim ; How is the gas existing to quickly ?. I'm not sure I follow this exactly ?.

When the primer is struck powder goes off gases expand pushes projectile out while simultaneously expanding case neck thus sealing chamber . Correct ?. I see NO evidence of residue of leakage around neck or on shoulder .
If necks were pushed back and undersized it would surely show spend powder residue around there . Correct ?.
I will put it all back together and fire several rounds to see if it does it with the plug in .

I'm not shooting cast bullets !. Jacket ammo only 150 165 168 174 according to manuals I'm maybe 100 -150 FPS slower than Military max pressures .

I have chronograph loads .I have no peizzo load cell for pressure checking though .

Many Thanks to ALL of you for your input .
This is kind of like having a tick on you !. One which you just can't seem to remove .

i'm not sure why you want a single shot m1, but some years ago we modified a few for a vfw post, but did so by drilling a hole into the gasplug, i don't remember the size, but it wasn't very big

Dr. K, I cited cast bullet loads as examples of low pressure load which frequently exibit backed out primers. I am aware that your loads have jackeded bullets, but such loads will also back out primers if pressures are low enough. The mechanism is as follows, when the firing pin comes forward it pushes the cartdrige case forwrd until the case shoulder is stopped by the chamber shoulder. It may in so doing shorten the case slightly if the spring is powerfull enough. A Garand usually is. The powder ignites, and, if pressure rises high enough, the case walls grip the chamber and the case streches until the case head is supported by the breech block or bolt. If pressure is too low, the case refuses to strech, and the primer backs out until the breech block stops it. Try increasing the charge to high end book loads, I'll bet the primer backing out stops happening.

I concur with Slowpoke Slim. I believe your problem comes from TOO LOW pressures, rather than too-high pressures or excessive headspace.....

Put the gas cylinder plug back in and fire 8 rounds of M2 Ball ammo. Look at the case heads of the empties. I'll bet they're OK!

I will put the adjustable plug back in mine and see if the problem persist .
I still fail to see how pressure is falling off to quickly so as to allow low pressure syndrome . .

The object was not to have a single shot , just for load development .

Slowpoke Slim and Driver have valid points as do the rest of you .I shall try all suggestions over the weekend and report back next week .

Only one thing worse than having a problem is never having feed back as to it's resolve . That wouldn't be the case here . thanks All ...

OK ; Sports fans !. Preliminary report . Full semi auto function my problem solved !. Ok well kind of !?.

My buddies did it after 5 shots again on the 8 th. shot . Second magazine second shot and six shot !. Then mine did one with the second magazine I believe it was the 4 Th or 6 Th. shot !.
Now remember His was checked for head space a few years back , mine never has been !.

We loaded H & IMR 4895 as well as BLC-2 all three were in the upper load level . Like one grain under max !. Blc-2 was 50.0 grains H4895 was 46.2 grains IMR 4895 was 50.5 - 51.2grains the last load was a shoulder banger !!!.

So now what ?. I couldn't get mine to do it again with or with out military brass . His did it with both his loads and my loads !. We did clean the gas port before reassembling both of them !, Should I have a Quality GunSmith check them I mean really check them ?. Not just gauge the dam thing !. It's not ruining brass or sticking or causing any problems other than primer back out !. It's .012 -.015" but it still bothers me !.

Doc,

That's an odd one, for sure...

Tell me about your brass. You said commercial does it and military doesn't? You're uniforming your pockets, I see. On both brass types, military and commercial? Or are you just uniforming the commercial brass. Is all the commercial brass from the same batch/lot, or is some of it mixed? How do the primers "feel" when you seat them? Do they seem to seat with proper resistance? Can you easily push out a seated primer from the inside? You're not getting smokey cases when they've been fired, whether the primers stay in or back out? What's the diameter difference between the diameter of a resized piece of brass vs. fired brass normal vs. fired brass with primer backed out (when measured at the casehead, the mid-point, and right at/below the shoulder)? Are you seeing a big difference in brass diameter? If you have a headspace problem, I would think it would be blowing your brass size up in size, or setting the shoulder forward, even when the primers aren't falling out.

How's the throat area? Do you have excessive "lead" area in the throat? How far out can you get a seated bullet to sit and still chamber and close the bolt? If you take the recoil spring out to eliminate the bolt slamming the round into the chamber, you can take a dummy round, starting with the bullet sitting out way too far (so you know it won't chamber) and try closing the bolt by hand (once again with the recoil spring out of the rifle. Slowly seat the bullet deeper with your seating die and progressively checking for bolt close, until you get the bolt to "just close" on the dummy round. This will give you a good idea of how much lead your throat has. It may (?) be excessive.

Are these DCM guns, parts guns, or Korean re-imports? I've seen some of the "Blue Sky" Korean imports with some pretty shakey barrels (shot out/big chambers/too much headspace).

Is this the only bullet/powder combo that does it? (Sorry, just re-read that 3 powders do it) I never loaded that powder (any of those powders) for my Garands, so I'm no help to you there. My load has always been Win 748 47.5 gr with a Sierra 168 gr Matchking, loaded just short enough to clear the mag well.

The sequence that occurs on firing is; The primer pushes the case forward and protrudes back a scosh. When the powder burns the case stays forward until about 40 kpsi or so (this is why low pressure loads result in short cases). Then the forward part of the case stays stuck to the chamber and the case stretches back resetting the primer. If the pressure was high enough to bulge the primer a bit it will hve a "rivet" look. Black on the case mouth is more a sign of slow powder than low pressure.
Good Luck!

WOW to much info !.

let me try and explain every thing I do and my shooting buddy does .

Cases are varied , head stamps commercial , military L C only !. Most are match once fired by either him or my self . ( They were new ) . Commercial brass is a hodge podge collection .
Some new some not . ALL are carefully Neck sized , unless I've never fired them out of my weapon ; then full length then neck size .

Primer pockets are swagged on a Dillon for L C head stamp military only , to a uniform depth of .127 !. All pockets are .2085 - .209 primers are .212 - .214 Depending on manufacture they do vary slightly but not always !.

I seat my loads .030 - .045 under max length
my partner goes max length . I think that's why he uses the sled and not semi mode mainly .

These are NO IMPORT or Parts guns !. That I can assure you of !.

A couple of these are used and a couple are pristine !!. Made NO difference by the way as to which was what !.

We exchanged loads of a variety of commercial L C and powders of various charges !.

Neither of us get smoke or lead around neck or in the chamber . ( We cleaned the crap out of it totally chamber brush before reassembly to insure this ) brass is trimmed to length before we load even weighed of course visual inspection before anything is done .

I shot mine today and it didn't do it once so I opened my gas port plug adjustable type so as not to engage the opp rod . NEVER did it 120 rounds !!!!!!!!!!!. My partner wasn't here but will be here Friday , so we shall give it another go .


We are going over Sat. close to Pendleton Marine Base to see an Old Gunny who happens to be a Smithy . He wants to see this in action !.
Of course now mine wouldn't do it at all today

My partners will for sure !.

Thanks for the interest I'll keep you posted .

Head space is .015" in his M1 !. Mine is .007"
Gunny says that's not uncommon in Military shit !. So he took it and is going to " whack it " were his exact words !. I know what he's going to really do to it . My partners eyes got big as silver dollars when he said that !. You had to be there !.
Gunny will fix it if anybody can Ex Marine 30 years , almost as a many as a gunsmith !.

Ya pick er up next Sat. boys !. We replied Semer Fi Gunny !. As we closed the door I heard something about the best part of you ran down ; and the door closed !. He's a colorful sort , but a real stand up guy !. I don't think anything has been made he hasn't fixed .
My shooting partner is 68 years young !. I'm the baby at 56 !.

Two things come to mind - sizing die induced excess headspace and the simple fact that an M1 will actually set the shoulder of a cartridge back when chambering.

The proper way to set a sizing die up for an M1 is to strip the bolt and incrementally increase sizing until the bolt just drops into battery. Or use a Stoney Point gauge.

Hatcher stated in one of his books, and I don't remember which one, that an M1 will set the shoulder back about 0.007" when chambering. This can be verified using a Stoney Point gauge. Measure a round, chamber, extract and remeasure. I've found some will even set the shoulder back a bit more than Hatcher wrote.

We need to remember that these were battle rifles and tolerances tend to be a bit more than on commercial. They are not gentle on cases and John C. probably didn't reload.

I concur ; As soon as Gunny Whacks Bills M1 we will head back to my place and put some rounds through it . Then we shall see if the Whacking did any good ?.

I always knew military weapons were on the lose side for obvious reasons . One just never knows how lose !?. ...

A successful Whacking !. head space was a little to much . Gunny reminded us of two important things . First the military never intended for civilians to own reload or operate these weapons !. Grunts don't press primers or resize cases or use dies , they fill magazines and fire upon their targets !.

Next one never knows who has fiddled with a particular weapon or where they were trained .

It now works with or without opp rod connected !.
When I questioned him about the other gunsmith checking head space , he looked at me kind of peculiar shook his head and replied . F ing Amateures couldn't find their way out of a closet . Didn't know or actually didn't check it !. Either way it works just fine now !.
Thanks to all who took an active interest !...