New Made Commercial M1 Carbine Barrels
Just got back from the Nationals at Camp Perry and this year I replaced over a half dozen barrels with new commercial barrels from Gun Parts and Fulton Armory. I “think” the barrels are made by the same maker, though I can’t be absolutely sure.
Some of these barrels used to have (and some still have index marks on them) for alignment to the receiver. Some barrels have no alignment marks. My advice is NOT to trust the index marks on the barrels in many cases or at least check them out carefully. I’ve seen some of the front sights on a small percentage of these barrels to be as much as 4 ½ degrees out of agreement with the index marks or bottom rear flats on the barrels. The good news is that on these barrels, the furthest from TDC was about 3 degrees and the average was they were off at most 1 ½ degrees.
There is another thing that is common on almost everyone of these barrels and that is the fact that full size G.I. pistons are WAY too tight in these barrels. That can be a good thing if you have a really worn G.I. piston, but it will cause a malfunction with a good condition G.I. piston.
Here’s what I came up with to solve these problems.
The first thing to do is fit the piston to the barrel. You don’t HAVE to have a lathe or grinder to do this. You can put the piston in a drill press and carefully take metal off the diameter of the piston until is just barely moves freely in the barrel. I suggest stones and emory cloth for this, though you might use a diamond file carefully to get the majority of the metal off. Finish polishing with a stone. We are talking a few thousandths of an inch of metal that has to be removed to free up the piston. After that, tighten down the piston nut and make sure you peen the barrel two of the notches in the nut so it won’t back out during firing.
Then mount the front band and front sight on the barrel. Then put the barrel in the vice with the front sight pointing away from you and the barrel is held so you can get at the lower flat on the rear of the barrel. Take an angle measurement off the front sight BLADE using a steel scale (rule) held tight against the side of the blade and extending past the muzzle where you can put an angle finder on it. Then take an angle measurement off the bottom of the barrel flat in the rear. That will tell you how far off the front sight is from the flat of the barrel and makes alignment a WHOLE lot easier. Many carbine collectors have informed me that original carbines had the front sights off top dead center by as much as 3 ½ to 4 ½ degrees on original carbines and their barrels. That’s good to know info and helped me come up with this method. It is ALSO good to know the acceptable standard for standard Garand and Carbine Barrels is that they can be off a full degree either plus or minus off Top Dead Center. That gives you some “adjustment” room to get the front sight as close to TDC as possible. If the front sight is a little shy of TDC, then you can mount it with the bottom flat against the receiver a degree past TDC and that should better align the front sight. If your front sight is a little beyond TDC, then you can mount it so it is a degree less than center on the bottom of the barrel to the receiver. Hope this makes sense. Doing it this way not only aligns the front sight as well as possible, but ensures the slide and other parts will work freely and correctly.
I spent weeks trying to find a pull through Carbine Reamer a few months ago and almost no one is making them anymore due to low demand. So many of us have to use a standard reamer, but we don’t want to have to put the barrel on and take it off many times when cutting headspace in the chambers. Many of these commercial barrels originally index WAY off TDC when you hand tighten them. What I’ve found is best to do is tighten the barrel to about 45 degrees from TDC then take the barrel off the receiver before cutting headspace. You will have PLENTY of barrel shoulder to torque the barrel on when you do that. Then CAREFULLY cut the headspace until a NO GO Gage made by Clymer or JGS will just BARELY allow the bolt to begin to close down on the right receiver bolt engagement surface WHEN you hand screw in the barrel into the receiver and it has not been tightened down. What I prefer is the bolt will close about halfway down and/or there is resistance/friction when the bolt goes all the way down. When you torque the barrel down into the final position, that will give correct headspace on the GO gage and the NO GO gage won’t allow the bolt to close. Carbine barrels had a tendency to be looser than Garand or M14 headspace and I think that helps function.
Then taking care to be mindful of how the front sight aligns on the barrel, tighten and torque the barrel down to TDC or a degree less or more so the front sight sligns as close to TDC as possible from the information above.
The last thing is that at least 40 percent of these new carbine barrels had muzzles that really need to have the crown on the ends of the lands cleaned up. I made it a practice to use a muzzle crowning tool on all of them, even if only a very little metal was removed.
I’ve had good reports from these barrels as to function and accuracy as long as one keeps these things in mind.
