View Full Version : Threading M1 Carbine barrel into reciever
03-26-2009, 04:29 PM
I was contacted by someone that wanted me to make a holding fixture for a WWII M1 Carbine reciever and barrel so the barrel could be screwed into the reciever. Maybe reciever is not the right term. The barrel needs to be rotated about 80-90 degs so some tick marks line up, so he told me. Not being a gunsmith I think there is more to just tightening up the barrel until the marks line up. Can someone give me some guidence?
03-26-2009, 05:59 PM
Basically on the carbine you tighten the barrel until the tick marks line up. You do need to have the right amount of "draw" prior to tightening. Too much and you won't be able to rotate the barrel far enough; too little and the barrel won't be tight enough when indexed properly.
After I finish dinner I'll look up the draw necessary.
After installation you need to finish ream the chamber. The required pull through reamer can be rented.
03-26-2009, 08:52 PM
So I looked in Jerry Kuhnhausen's manual and the "rotational draw" spec is 1/16" min 3/32" max. Meaning that after the barrel is hand tight there should be 1/16" to 3/32" left to go before the tick marks are aligned.
The threads are .750"-20 in case you need to remove material from the barrel shoulder. You should be able to calculate how much to remove from that.
Depending on the barrel your friend has and exactly what he needs you to do, you may also need to swap the gas piston over from the old barrel to new. Also, the front sight might need to be moved. The front sight is held on with a drift pin and has a square key in a keyway to keep it from rotating.
I believe there is a special tool to pull the front sight off once the pin is drifted out, like a gear puller. I drifted mine off with a brass rod.
Removing the gas piston nut takes a special spanner wrench. They aren't too difficult to make.
I made my barrel vice and receiver wrench from aluminum bar stock. If you need drawings I may be able to dig some up.
03-28-2009, 06:39 PM
Do you mean there should be 1/16" to 3/32" between the tick marks? Sounds like about 20 degs. His is more that 1/4", more like 45 degs of rotation.
03-28-2009, 09:11 PM
According to Kuhnhausen, yes, 1/16 to 3/32 between the tick marks. He does have a note in the text that "M1 Carbine receivers are faily forgiving and barrels are often installed with higher draw".
04-02-2009, 05:06 PM
Is there any reaming or other tweeking required after the barrel is installed??
04-02-2009, 05:10 PM
Depends on if the headspace is within specs or not.... :o
04-02-2009, 09:07 PM
I like to use about 1/8 turn worth of barrel draw on semi-autos, about 1/10th on others. On your carbine, if it's a brand new old stock military barrel and also military receiver and bolt, you will probably have to ream the chamber to get the correct headspace. If it's a used barrel, like Highpower said, "depends"... Remember the First Law of Gunsmithing..."always work on the cheapest or most easily replaced part first", which in this case would be the barrel. Hopefully, if it's got short headspace, it won't have a chrome plated bore!
04-10-2009, 01:54 PM
If you have 20 threads per inch Then one turn of the barrel equals .050" off the shoulder. So half of a turn would equal .025" off of shoulder.
1/4 turn would equal .0125" off shoulder.
1/8 turn of barrel would equal .00625" off shoulder.
1/16 turn would equal .003125" off of shoulder.
If I was doing it I would make it a .002" interference fit.
I believe this is what your asking. Head space normally runs between .002" and .008" with optimum being .004"
05-07-2009, 03:24 PM