When shooting an M1 Garand and here I am talking about a service or field grade rifle not a match grade rifle, there are three areas to check. Like buying a used car there are usually a few areas you want to examine to insure the car will operate properly. Three areas to check that will ensure your Garand will shoot fairly good groups are tightness with the gas cylinder, rear sight, and stock lock-up.
The gas cylinder is held in place by three splines on the barrel, the gas cylinder lock, and gas cylinder lock screw. What is important here is that there is no movement, wiggle side-to-side of the gas cylinder on the barrel. A loose gas cylinder will effect grouping or cause several groups on your target. There is an easy fix to eliminate this problem.
What you will require is a ½ inch socket, small hammer, 1/8 inch steel punch, and block of wood. When looking at the barrel from the muzzle end there are three splines, one at 12 o.clock, another at 4 o.clock, and another at 8 o.clock. You first want to lay the barrel with the top spline up and the 6 o.clock position of the barrel on the block of wood. (See figures to the right)
Lay the ½ inch socket along the spline approximately 1/8 inch from the front of the spline which makes it easier to get the gas cylinder started when installing on the barrel. Hit the socket with the hammer a few times to slightly bend in the spline edges. You do not have to overdo this. Next turn the barrel to the spline at the 4 o.clock and with the 1/8 inch punch and hammer peen along the spline (just one side) along the top, center, and bottom a few times. (See figure to the left) Again, you do not have to overdo this. Do the same for the 8 o.clock position and you are almost done. An option is to use the ½ inch socket on all splines.either method will work.
The final step is to re-install the gas cylinder on the barrel. Slide the gas cylinder onto the barrel and push into place. It may be necessary to hammer into place with a block of wood. Be sure to align the window in the top of the gas cylinder with the gas port hole in the barrel. There should be a space slightly less than a dime's width between the gas cylinder and the stock ferrule. This allows for expansion of the handguard eliminating binding against the gas cylinder and changing the POI as the rifle heats up during firing. Take the gas cylinder lock and turn into place. Ideally it should stop at the 6 o.clock position. If it goes slightly beyond that.s OK. Lastly, take the gas cylinder lock screw and tighten down onto the gas cylinder lock by screwing into the gas cylinder. The gas cylinder should be good and tight with no side-to-side wiggle. Next time I will discuss the rear sight.