Problems with Schuster DCM Gas Plug

[Phil McGrath]

Ulrich, provide that everything is lined up on the front end of you rifle, I would try removing the adjustable gas plug and return too the stock one, or if you have alot of gas leakage where the gas cylinder and barrels gas port meet, you could try too peen the two bottom splines on the barrel too get a better gas seal.

I have 2 M1's my 30.06 has slight leakage and after a few rounds it stops/plugs up it has never failed too work with surplus or reloaded ammo and standard gas cylinder parts. My number 2 M1 is in 7.62 it is a USGI SA 7.62 barrel and the gas cylinder fit is very tight it needs too be driven on with a block of wood there is no gas leakage with standard parts, my point is that lite leakage is ok as long and the rifle works, extream is another you will have too deside.

Jerry Kuhnhausen's US .30 Caliber Gas Operated Service Rifles Shop Manual Vol 1/2 pg 118 shows how and where too peen the splines for a better seal.

Here's a few questions that can help us out, did the rifle work before it was rebarrelled, you didn't say what barrel you are using now? whats the gas port size in the barrel, what brand/type of ammo that has worked or if your using reloads what is the load data these all are factors that contribute too the rifles operation.

[jmoore]

Master Gunnery Sgt. Gus Fisher noted the following specs for the 7,62x51 M1 Garand gas port:

"So they went with a .106" diameter gas port, though the rifles will function fine with a .096" hole."

"...(I) got so used to mounting them that I was dumbfounded when one would not function correctly during function fire. I had my gages with me and swapped many parts to see if I could get it to function and it would not. Classis case of short recoil. So I took it home and did more than a field strip and could not initially figure out what was wrong. Then it hit me, "Stupid, it HAS to be something about the gas system!!" Well, it wasn't the gas cylinder, piston or anything else. I stared at the gas port for five minutes before it dawned on me to check the size. Sure enough, it was .078" like a .30-06 barrel. So I drilled it out, reassembled the rifle, went back to the range and it worked perfectly..."

Items in bold are my doing. Referenced from elsewhere...With notification to Gus Fisher, too, just to prevent dramas.

[Daimler1989]

Hi guys,

thanks for your thinking about my problem. I bought the gun one year ago and it did not function properly from the start. This is a built rifle by a german gunsmith who is well known for his work on the M1 Garand - it is built with refurbished parts, an new barrel and new furniture. With the original gas plug it works with some brands of ammo and does short stroke with most others. That's why I wanted to try the Schuster plug and failed to solve the short stroking problem. I don't know the exact measurement of the gas port, but the smith told me, he had opened it up to maximun, when I gave him the gun back for repair for the first time after it had failed on the range. So I fear that the gas cylinder is the problem or even the outer barrel dimension, as I can't imagine another point where the gas might escape. Interestingly, the brands of ammo that makes the gun cycle fully, show flattened primers - which means, the chamber pressure is quite high.

The main problem here in Germany is that you must have an official permission to buy a gun, and when you own it, you can sell it, but you have to apply for another permission to buy a replacement - which is quite time consuming and needs a lot of correspondence with the authorities. Gun smiths know that and thus often are quite lazy to solve your problem after you have paid them for a gun - because you want to avoid a long journey to buy a new gun instead of having the old one repaired, and they can dictate the rules... I guess I will try to make the smith check out gas cylinder and barrel dimension and insist upon replacing the part that is responsible for the gas leakage, because I still have one and a half week of warranty time.

I will keep you informed
regards
Ulrich

[Charlie59]

Have you checked the muzzle for excessive wear, and the gas piston?
Charlie

[jmoore]

If you can find a 2,5mm drill bit, that should be almost the max size of the barrel port. It should probably be a snug fit for proper function, a tiny bit loose would be OK.

A 2mm drill bit is about the size of the 30-06 port (it's actually a little big), so it should rattle around in the hole. If it won't go or is tight, then there's your problem!

A small expenditure on your part could eliminate a fair amount of mystery! And possibly keep the "smith" from feediing you a line of "nonsense".

Have you checked the muzzle for excessive wear, and the gas piston?
Charlie

It's a new barrel...

[Bill Hollinger]

Check the gas cylinder alignment. I had an M1 do this to me and come to find out the gas cylinder lock was not tight so tightening up the gas cylinder lock screw didn't fix it. I had to turn the gas cylinder lock two full turns. In other words, the gas hole was not aligned. A hand guard that is too long or has the metal insert not seated can cause this and so can a misaligned hole in the barrel.