MasterGunner
Member
- Location
- Machesney Park, IL USA
"I recently bought a M1 Carbine and when I took it to the range it would only fire single shot and not semi. I discovered that the piston and piston nut were missing. I have the parts now and I don't know how far to screw the piston nut in. Is it crenellated end toward the butt plate and screwed in until all the threads are covered? I managed to screw it in until about one eighth of an inch of thread is showing. I don't have the proper wrench and didn't want to force it. Also there is a small hole in the edge of the piston nut recepticle, is this for a pin (which I don't have)."
Let's tackle the obvious first: the hole that you think is for a pin, is actuall the hole left by the drill that made the gas port. Do not try to put a pin in this hole!
There are actually two kinds of Carbines; (1) those produced under government contract and (2) commercial copies made with military parts. On a G.I. carbine barrel, the gas piston nut has three large notches, 120 degrees apart and three small notches 120 degrees apart. The large notches are for use of the gas piston nut wrench that's used to remove and install the nut. The small notches are used as places to stake the nut with a prick punch to keep it from backing out during firing.
Commercial copies of the carbine barrel may be found with four lugs for a commercial nut wrench. The U.S. carbine nut wrench is available from Numrich Gun Parts or Sarco, Inc. They can probably supply an aftermarket wrench that had both military (3-lugs) and civilian (4-lugs).
Specs: The gas piston nut threads are: 0.500-32 NS-3. There are two kinds of piston nuts: old with a chamber on the side opposite the wrench lugs (do not use) and the new type that has a 0.0.030 + 0.005 inch deep by 0.402 + 0.010 inch counterbore oposite the wrench lugs (use this one). Interior diameter of the nut is 0.303 + 0.002 inch.
Gas pistons are T-shaped. The smaller outside diameter is 0.300 -0.001 inch by 0.705 -0.010 inch long, the larger diameter is 0.3997 -0.0005 inch by 0.140 +/- 0.003 inch wide. There is a hardness test mark in the end of the small piston O.D.
Installation: [This assumes the old nut has been removed or fallen out.] Use a needle file to remove the raised metal caused by staking of the old piston nut. Spray the piston and nut with WD-40, then install the piston in the nut so that the piston O.D. mates with the counterbore in the end of the nut. Screw the nut into the gas cylinder of the barrel. Use the piston nut wrench to tighten the nut until it bottoms out. Locate the most accessable staking notch. Use a hammer and prick punch to stake the nut in the gas cylinder so it does not back out.
Let's tackle the obvious first: the hole that you think is for a pin, is actuall the hole left by the drill that made the gas port. Do not try to put a pin in this hole!
There are actually two kinds of Carbines; (1) those produced under government contract and (2) commercial copies made with military parts. On a G.I. carbine barrel, the gas piston nut has three large notches, 120 degrees apart and three small notches 120 degrees apart. The large notches are for use of the gas piston nut wrench that's used to remove and install the nut. The small notches are used as places to stake the nut with a prick punch to keep it from backing out during firing.
Commercial copies of the carbine barrel may be found with four lugs for a commercial nut wrench. The U.S. carbine nut wrench is available from Numrich Gun Parts or Sarco, Inc. They can probably supply an aftermarket wrench that had both military (3-lugs) and civilian (4-lugs).
Specs: The gas piston nut threads are: 0.500-32 NS-3. There are two kinds of piston nuts: old with a chamber on the side opposite the wrench lugs (do not use) and the new type that has a 0.0.030 + 0.005 inch deep by 0.402 + 0.010 inch counterbore oposite the wrench lugs (use this one). Interior diameter of the nut is 0.303 + 0.002 inch.
Gas pistons are T-shaped. The smaller outside diameter is 0.300 -0.001 inch by 0.705 -0.010 inch long, the larger diameter is 0.3997 -0.0005 inch by 0.140 +/- 0.003 inch wide. There is a hardness test mark in the end of the small piston O.D.
Installation: [This assumes the old nut has been removed or fallen out.] Use a needle file to remove the raised metal caused by staking of the old piston nut. Spray the piston and nut with WD-40, then install the piston in the nut so that the piston O.D. mates with the counterbore in the end of the nut. Screw the nut into the gas cylinder of the barrel. Use the piston nut wrench to tighten the nut until it bottoms out. Locate the most accessable staking notch. Use a hammer and prick punch to stake the nut in the gas cylinder so it does not back out.
