M1 Garand/adj gas plug range session question

[Ditch-Tiger]

Just got back from the range where i shot my M1 Garand with newly installed McCann adjustable gas plug.
Works great and it is wonderfull to be able to shoot factory ammo as i personaly hate to reload. (sorry, just to time consuming/tedious for my taste)

My question is...
I was under the impresion that one is suposed to install the biggest jet/port and fire one round. If it locks the bolt back, then your good to go with that type of ammo. If it doesn't, you put in the next smallest jet/port until it will fire and lock the bolt back.
Anyway, i installed the biggest one and headed to the range fully exspecting to have to change the port at least once before finding the correct one.
I loaded one round, fired and the bolt locked back without needing to change ports...
Is this normal, or do most factory rounds work with the biggest port?
Sould i be worried that the largest port may not be bleeding enough gas and may still cause damage to the op rod, or am i just being paranoid?

 

[dmazur]

You can get a "numbered" drill set and determine the orifice size by trial and error, of the largest insert screw.

Then, if you aren't going to be using the smaller ones, you can drill them out to larger orifices. There isn't much difference in size, as a small change in bleed orifice makes a big difference in force.

I read that someone made custom orifice screws by drilling the screw with a fairly large bit, brazing the end shut and then drilling through the braze with the smaller orifice drill size.

I agree with the thinking process, which essentially is, "If I haven't opened it enough to make it fail to cycle, and then move progressively smaller, how do I know I've opened it enough?"

I don't really have an answer for you, but the above is a suggestion.

 

[krs]

Kinda' hard to give you an answer without you saying WHAT ammo as in what bullet and charge you are trying. There's TONS of different "factory" loadings.

Personally, I think that you're playing with fire and don't know how badly it could hurt you.

 

[Ditch-Tiger]

krs,
How so?
Are you talking about the reciever "failing", or the op rod breaking because factory rounds are to hot? if its the latter, that is what the adjustable plug is for.

If your worried about the gun blowing up and that is a legitamate possiblity, then why would several manufactures make adjustable gas plugs to allow the use of factory ammo?

FYI- The ammo i used is Federal's blue box (cheap) 150gr SP

 

[D94R]

krs, I agree with asking what the "factory" loading was. However, don't condemn the man with your second sentence. That is why he asked on here, to avoid the "fire". You added nothing helpful with that.

 

[rskent]

I thought you were supposed to start with the smallest and work up.

Steve

 

[C-grunt]

I thought you were supposed to start with the smallest and work up.

Steve

Im not familiar with the procedures but this makes more sense to me than go big and down. The whole point of the adjustable plug is to tame the cycling forces of modern ammo right? So shouldnt you start with the smallest and move up until it has enough force to properly cycle?

If you start with the biggest port, how do you know its not locking back because its being slammed really hard?

 

[rskent]

C-grunt
You explained it much better than I could.

Steve

 

[krs]

Either way is dangerous if the load is unknown.

That this one WAS locked open by firing an unknown load with "the big screw" means the round must have been pretty heavy and it was for that ignorant move that I said the playing with fire stuff. This guy came in asking about what happened AFTER he'd done his trick, not before, and THAT was playing with fire.

Close it down entirely, or solid plug, is what was used until there was a need for the rifle grenades which increased pressure enough to break the back of the receiver away using service BLANKS. So they designed a spring loaded valve that would open as needed but still operate the rifle with service loads.

I'm with Clint McKee on this, modified to say that all of these kids who buy Garands because of whatever and then first thing get those silly orifices to screw with the design are playing with fire.

At least a factory round probably won't have a high primer, although I'd almost be hesitant to say that these days, so at least factory ammo shooters are less likely to enjoy the slamfire their reloading friends are destined to blame their rifles for, because it couldn't be their long reloading experience. After all, they learned to use their progressives from other bozos on utube.

minor rant off with a recommendation to read through the Fulton armory FAQ's

 

[dmazur]

First, I belong to the "do the research, then proceed carefully" school, rather than the "don't do anything because you're not an expert" one.

So, in order to proceed carefully, you have to understand the process, at least at a fundamental level.

Im not familiar with the procedures but this makes more sense to me than go big and down. The whole point of the adjustable plug is to tame the cycling forces of modern ammo right? So shouldnt you start with the smallest and move up until it has enough force to properly cycle?

This would be correct if the adjustable plug was between the barrel and the gas cylinder. However, it is not. It vents excess pressure to atmosphere, with the remaining pressure available for the cylinder. Therefore, you need to start with the largest orifice and work smaller until you observe reliable cycling.

As stated in another post, one grenade launcher design had a strut that opened a valve in this plug, to reduce pressure developed during grenade launcher use. So the idea of venting gas to regulate pressure isn't a new one.

 

[benzy2]

I use the Schuster nut and if you back it out far enough I haven't found a single factory load that will cycle. I know you have your money in the current nut but I would rather spend another $20 and be able to get the rifle to not cycle than to hope you have bled enough pressure to remain safe. This is the problem with insert nuts though. If they aren't right you're out of luck. They are simple to switch too but not as adjustable as a screw style adjustable nut.

 

[jpwilly]

Schuster is virtually infinite in it's adjustment range witch is why I chose to use it. Yes it can turn your semi auto into a straight pull single shot bolt action with any load...removing the gas plug would do the same.

Anyway, I've very courious about the loading that the OP shot where the largest gas jet screw cycled the action?

 

[Ditch-Tiger]

jpwilly/benzy2,
More than likley i should abandon the Federals and try a differant factory load that will fail to cycle with the largest port, any sugestions? What have you used in yours that you had to adjust your plug ALOT, that might work better with mine?

 

[CZguy]

jpwilly/benzy2,
More than likley i should abandon the Federals and try a differant factory load that will fail to cycle with the largest port, any sugestions? What have you used in yours that you had to adjust your plug ALOT, that might work better with mine?

Or, you could abandon your gas plug and try an adjustable one.

 

[Acera]

You might want to check out the CMP forums, they are the experts in the area of M1 Garands. They are just a friendly and helpful as a lot of the people on here are.