M1 Garand: .35 Whelen Conversion

This article is a written overview of performing a caliber conversion on the M1 Garand for those with machine shop knowledge and an understanding of M1 operation and assembly. I disassembled an as-issued M1 and replaced the military barrel with an Adams & Bennett short-chambered .35 Whelen barrel threaded for a Mauser action. The first step was machining the threads off the barrel and rethreading to fit the Garand action. Next, I installed the barrel and placed assembly marks.

Before chambering the barrel, I fit the bolt to insure both lugs were making full contact. Using a chambering reamer, I finished the chambering to a 0.005" headspace. The barrel was then removed and I placed the right and left bullet guiding grooves using dimensions taken from the old barrel. The area inside the receiver just ahead of the cartridge guide needed to be made bigger side-to-side (0.860) for the larger 35 Whelen with optic. diameter bullet.

I installed the barrel for the final time using the assembly marks as a guide. Gas Chamber In order to maintain strength, I made the gas chamber from one piece of steel round stock 1" in diameter and 7" long. On my lathe with a fourjaw independent chuck, I located a point 3/16" off center and drilled a center hole. I used alive center in the tail stock to support the piece. I then turned the piece to a diameter of 21/32" in the center of the piece 4 1/2" long.

This left me with enough material on each end to cut mounting tabs. I used my shaper to cut the tabs 3/4" long, 3/8" wide, and 3/16" thick. I drilled two holes for mounting 8×40 screws in each tab. To drill the bore, I used my lathe with a three-jaw chuck and drilled a bottomed 33/64" hole 5 1/8" deep to the edge of the drilled hole. The hole was reamed to 0.525" and polished to fit the operating rod piston.

I drilled two holes into the bottomed end of the gas chamber, with one hole drilled and tapped to 10×32 for the gas tube and the other hole drilled and tapped part of the way through the hole for a 4×40 screw to be used as a gas bleed. The holes were drilled to enter the gas chamber at the edge of the inside of the bore to be able to access the mounting screws without removing the gas tube.

I drilled two 4×40 screws longitudinally, one with #59 drill for a 0.041" hole (brass colored) and the other one with a #56 drill for a 0.046" hole (silver colored.) You may need other sizes. Bottomed holes were drilled in the barrel to match holes in the mounting tabs and located so that the gas chamber hole is 6 5/8" from the face of the receiver. The original operating rod is cut or shortened and may have to be heated and bent to fit the gas chamber without dragging on the bore.

I made a button to fit into the end of the operating rod and the inside of the gas chamber. The cylindrical portion of the operating rod is 5" from the shoulder to the end. Installing the operating rod may be just a little tricky. Turn the operating rod so that the catch portion of the rod is between the receiver legs and then can be inserted into the gas chamber. This allows the rest of the receiver parts and operating rod springs to be installed normally.

I found that the original operating rod spring could not be modified for use in this application. Gardner Spring supplied me with a spring 0.380" in diameter, 12" long,, with a wire diameter of 0.0475, and a coilto-coil distance of 1/8" or more to give enough room to compress the spring without collapsing on itself.

35 Whelen, shown disassembled. The gas tube is 3/16" stainless steel tubing threaded 10×32 on each end. The length of the tube will be determined by where you locate the gas port hole. To locate the gas port hole in the barrel, I slugged the barrel, removed the slug, marked it at the groove diameter, and pushed the slug back into the barrel until it rotated the mark to the bottom.

By measuring down the barrel to the slug and transferring this measurement to the outside bottom of the barrel, the distance from the muzzle to drill the gas port hole is accurately located with the port between lands. Drill the hole no less than into the bore. Using a #21 drill (tap drill), drill the hole just deep enough to thread the hole but not all the way through. The hole is tapped at 10×32.

Elbow Connector Block In order to connect the gas tube to the barrel and keep it as compact as possible, I made a right angle connector block from 3/8" keystock. I shaped one end of the block to match the barrel radius and then drilled through the block from the center of the radius side with a 13/64" drill. On the side opposite the radius, countersink the hole to accept the screw head.

In the center of the block at a right angle to the screw hole, drill a second hole (#21) into the first, but not through the block. Then, tap to 10×31. Connector Block Screw Drill a longitudinal hole 3/8" deep into a 10"x32"x11" screw 1/16" in diameter. Drill a 1/16" hole at a point 3/16" below the head of the screw. To produce a clearer path for the gas, reduce the diameter of the screw at the cross hole on the lathe.

The diameter of these holes may have to be increased in order to produce enough pressure to operate the action. This will depend upon the strength of the operating rod spring and the ammunition being fired. The amount of pressure to operate the action can be decreased by using different bleed screws in the gas chamber. For sights, I added a Burris Scout scope 2×7 with an eye relief of 18 to 21 inches. This sight works well for me. The success of this project depended upon my son, Scott.

My shooting shoulder has been surgically replaced, so he volunteered to test the completed rifle. AG American Gunsmith Reader Services 1.