Barrel Reit For The Remington Model 504 .22 Rimfire Rifle

The barrel on the Model 504 Remington is attached to the receiver via a joint that clamps a very thick split receiver ring around the barrel. This joint is tightened by a single size 10-32 socket head screw resulting in extreme thread stress if the barrel/receiver joint requires much take up. An apparent problem stems from the barrel shank being too small for the receiver hole.

The bore on the unclamped open receiver is 0.6750inch and the factory barrel shank diameter is 0.6690-inch on several of the rifles I have worked with. A practical solution to this problem when replacing or reworking a barrel is to increase barrel shank diameter nearer to receiver bore size and replacing the short 10-32 screw with a longer, hardened screw to utilize all of the existing threads in the receiver.

The work begins by making a section of test shaft to the precise diameter of the replacement barrel shank to fit the receiver. This will precisely indicate the required increase in barrel shank diameter for a proper fit while eliminating the need for excessive draw down of the clamping screw. The receiver hole diameter of the Model 504 Remington receiver of those rifles I examined is 0.6750-inch.

The un clamped receiver bore diameter is round with all parts of the inner surface or circumference equidistant from center. Attempting to tighten a 0.675-inch diameter receiver to a 0.6690-inch barrel shank will result in an elliptically shaped hole failing to coaxial align the barrel with the receiver, leaving a gap between surfaces. Further, the degree of torque required on a relatively small 10-32 22 LR rifles.

The factory issue barrel measures 0.6690" while the altered or replaced custom barrel shank is turned to 0.6740". 6745-inch as a pilot shaft to test for receiver/barrel fit. screw thread sets up an inordinate amount of stress on this screw. I turned apiece of brass stock as a pilot shaft to fit the open receiver bore as closely as possible. I made sure this test shaft fit the receiver bore of the two Model 504 Remington rifles I had available. Both bores were the same.

The diameter of the turned shaft was 0.6745-inch. It was necessary to cut a slot in the test shaft to fit the barrel locating stud inside the receiver. A trial fit then verified the exact size of the new barrel shank. At this stage of the barrel work I decided to re-terminate an existing Green Mountain premium barrel I had earlier fitted to the Model 504 Remington rifle receiver. This barrel had been turned to the factory specifications of 0.005-

inch under-size. With the barrel in the lathe, centered with live-center in the tail stock and steady rest set up, I turned the barrel shank to exactly 0.6745-inch and to correct length of 0.930-inch extending from the barrel shoulder. Then, before removing the barrel from the lathe, I cut the race in the shank allowing the end of the barrel to protrude through the inner stop ring within the bore where cartridge headspace is later established.

The chamber was then reamed using a Manson JGS Style Removable Pilot Match reamer. A Match reamer allows the bullet ogive to engage the lands on chambering as opposed to a F22 Bentz style reamer. The Manson reamer cuts a very precision chamber. The chamber is cut flush with the barrel breech plane allowing for the recessed case head, which is about 0.040-inch. The barrel was removed from the lathe, ready to cut the underside locating slot and the two extractor slots. I used a rotary key cutter to make the slots.

The laterally opposing extractor slots are cut and installed a few degrees counter clockwise from square, facilitating an angled case kick out as the case rim contacts the ejector on bolt withdrawal. One disadvantage of a Match style reamer is the difficulty to extract a fully chambered live cartridge. At least this was my experience with the three Match chambers used on the Remington 504s I worked with.

The hardened replacement screw with some lubricant does a perfect job of clamping the receiver ring to the barrel. As a later proof test I shot a group, removed and replaced the barrel and shot a second This work is performed in a milling machine. Though tapped at an angle, the longer screw has far more thread purchase than a shorter screw. group. It was a welcome sight to see that point of impact remained perfectly zeroed. There was a noticeable improvement as well in overall accuracy.

Groups that were in the 1/2-inch range at 50 yards were now at 3/10 and 1/4-inch. Analysis often reveals the source of problems in a firearm. When you know you have a well bedded rifle with a premium barrel and accuracy doesn’t meet standards it is time to examine closer. You just may find something, as was the case with these Model 504 Remington 22 rimfires. AG