View Full Version : M1 Carbine Short cycle

February 28, 2009, 10:37 PM
I have a M1 Carbine, I've had this rifle since I was a kid and it has had this problem for several years.

It is an Iver Johnson, the bolt is spotless, I Tried to find any burs and remove them, I couldn't find any, and removed the ones I could. New magazines have been used and I've used the most caustic cleaners I could find to clean the barrel and gas port.

I noticed that when I removed the removed the gas piston to clean it I didn't need a wrench to remove the gas piston nut, or replace it. I could not visually see any gas port to speak of, that seemed odd but it recoils.

Should I be able to see the that the gas port is clear on this model?

I've also never used any go-no go gauges, however but inspection of fired brass shows that it is always clean, no excessive discoloration. And I used a lager bore brush to clean the chamber.

I there anything else i can do before I send it to a gunsmith?

My dad has done some and he is stumped.

James K
February 28, 2009, 11:27 PM
Unlike the GI guns, those carbines had the gas port drilled first, then the cylinder installed, meaning that there is no hole through the cylinder to clean the gas port. Still, it can be done with a bent rod. The GI spec for the gas port is .070". Then, make sure the gas pistol and nut are installed correctly. The piston should protrude .031" from the nut when forward and 0.175" when back. When forward, the slide should contact the piston, not the nut.

The nut should not be screwed in tight; make sure the piston can move as stated above. In the other direction, the nut must not be loose or it can vibrate loose and let gas leak. If necessary, you can fire the gun out of the stock, adjusting the nut until things work, then stake it.

(I seem to recall that the IJ is a little different from the GI gun, so I am not absolutely certain all of that is correct, but I think it is.)


March 1, 2009, 02:42 AM
Thank you, you've given me about an hours worth of checks and even answered my looming question about the gas piston.
I bought my dad a M1 for christmas a number of years ago, visually they look the same. The biggest difference I've noticed so far is the stock, though my stock has been changed out for a M2. I read somewhere that IJ used a different recoil spring set up for thiers, mine appears to be identical to a GI.
this Rifle was "sold" to me from a Korean War Marine who told me stories of being stationed at the Marine School of Infantry, and I believed he added parts to make it a complete rifle before the sell.