Tightening a Gas-Cylinder the AFPG-way

[Dave Waits]

One of the biggest accuracy-killers on a M1 Garand is a loose Gas-Cylinder. The front sight is mounted on top of the Cylinder and, if the Gas-Cylinder is loose the front sight moves around every time the rifle is fired. I don't need to tell anybody here what that will do to groupsize. I've seen fliers at 200 yards that were six-inches away from the main group due to this.

There are two ways to correct this, three if you count a new Gas-Cylinder. However, an unissued Gas-Cylinder will run you about $125.00. So, we'll concentrate on the first two. Both methods involve tightening the barrel channels the Gas-Cylinder slides into.

Picture of Gas-Cylinder slot-channels;


The first uses a 1/2",3/8ths.drive socket, a Hammer, the barrel and a hard surface. You merely lay the socket in the slot and lightly tap it with the Hammer. You do this to all three slots and try the fit. Ideally, you want to be tight enough to require driving the Gas-Cylinder on with a plastic mallet. The tighter the better but, you don't want to batter or damage the slots. You just want to move enough metal into the slot to tighten the fit.

The problem with this type of tightening is that you can only do it once or twice before the slots are peened to the point of uselessness.

The Second method is by far the best. You need a small hammer, a hard surface, a 1/8th" centerpunch and, of course, the barrel. What you are going to do is put a dimple alongside the slot,front and back, about 1/16th." in from the edge on each side of all three slots. Be sure you center the barrel port in the Gas-Cylinder port before doing this so you can scribe a light mark on the backside of the barrel pad for reference. You only need to use light strikes on the punch to move enough metal to get a good tight fit. See below.


This is how they tightened Gas-Cylinders on the Air Force Premium-Grade M1 Match rifles. If the Gas-Cylinder loosens after several cleaning all that is required is to strike the dimples again with the center punch causing far less damage to the barrel.

Hope this helps

[Caleb]

Great information, thank you..