Making and Installing a Barrel/Receiver Coupler Sleeve

The Remington Model 504 rimfire action has the appearance of a modern high-power rifle. Its short, cylindrical receiver shows inherent strength with a full 1.2-inch diameter and a massive wall thickness of 0.294 inch. Nevertheless, close inspection suggests the rifle could be improved somewhat in the area of barrel-to-receiver stability. The 0.913inch-long barrel shank with a 0.671inch diameter is not threaded into the receiver.

Instead, it’s held in position by a split receiver ring with a #10-32 transverse barrel-clamp locking screw. A fair amount of torque is required of a screw of this size in providing ample clamping in locking the barrel to the receiver. The barrel is free-floating in its entirety, which places some additional strain on the barrel-receiver juncture, particularly if a heavier target barrel is used.

I devoted some study to the possibilities of strengthening the barrel-toreceiver union on rifle actions, with special attention to the Remington Model 504. After some consideration, I devised a viable means of strengthening the union in this area. The face of the Model 504s large receiver has a wide milled recess at the front, which also has a clamping action as the receiver screw is torqued.

I could see no significant purpose for this recess, however, aside from providing a shroud for the barrel joint’apparently for aesthetic purposes. Though the receiver recess is precision milled and functionally closed down as the barrel clamp screw is torqued, it doesn’t touch the barrel. I concluded that this recess was a perfect place to incorporate a sleevelike barrel coupler, which would fit precisely over the barrel and serve as an interface when clamped into the receiver recess.

The coupler would further be locked to the barrel by four 1/4-28 set screws triangularly positioned on the lower side of the coupler. This assembly would essentially double the length of the linear barrel surface contact to 1.725 inches extending from the receiver, and would add greatly to barrel/receiver rigidity. In theory, at least, I felt this should be a solid and worthwhile modification. A single precision part would do the job.

The coupler would also be bedded into the stock with Brownells super-strong Steel-Bed. Making the Coupler I used apiece of 416 stainless steel to make the coupler. The unaltered diameter was perfect, as it was taken from apiece of rifle barrel with a diameter the same as the Remington 504 receiver. In use, the coupler slips over and locks onto the barrel. In this case, the barrel had to be turned down some just forward of the factory barrel shank.

Four 1/4-28 set screws hold the barrel to the coupler when in use. I put the part in the lathe and completed the entire work before removing it to ensure total concentricity. The hole in the coupler was bored first at 0.800 inch. The step was then formed on the coupler to fit precisely into the receiver recess and butt firmly and squarely up to the inner surface of the recess. The length of the step is 0.116 inch, which was set up to the lathe carriage stop.

The diameter of the step must be absolutely perfect so it clamps together into the receiver recess as the barrel clamp screw is torqued. Both the barrel shank and the coupler step are clamped at the same time as the barrel clamp screw is tightened, so these two diameters must contact the receiver together. To accomplish this, I made two test parts to ensure a perfect hold of the parts as the barrel clamp screw is torqued. This is very important, particularly where more than one barrel is used.

Each barrel, of course, must receive the same attention. As the coupler was completed, I drilled and tapped the four 1/4-28 set- The action of the transverse clamp screw is shown here. From the top is the original Remington barrel with a removable sleeve (overturned portion of barrel) used to fit the barrel-to-receiver coupler. Second from the top is a Green Mountain barrel with a coupler in place, ready to use. Next is a Douglas barrel with a turned area, ready to use with a barrel/receiver coupler.

At the bottom is a Lilja barrel that has not yet been adapted for the use of a barrel/receiver coupler. screw holes used to hold and align the coupler to the turned portion of the barrel. The set screws were triangularly positioned on the coupler from below on 0.280-inch centers. I must emphasize this point: A test of the coupler must be performed to be sure the receiver clamp tightens on both the barrel shank as well as the receiver recess.

The barrel shank is 0.671 inch, whereas the closed receiver recess is 1.0145 inches as the receiver clamp screw is torqued. Additional barrels, as fitted, must agree (continued on page 21)

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precisely in diameter at the shank with factory specifications here. If the shank diameters are made undersize, problems in using the coupler will result. The barrel can be used in its original form by simply removing the coupler and tightening it into position with the barrel-locking screw. A sleeve can be made to slip over the turned portion of the barrel when the coupler is not in use, and retained with a small #6-48 set screw.

Conclusions Adding a coupler to strengthen the joint between a rifle barrel and receiver is a very worthwhile project. Mak- American Gunsmithing Association News Don’t forget to check out the center spread in this issue. Enroll in the AGI’s Complete DVD Gunsmithing Course and get an instant rebate of $200. As a professional gunsmith, there’s never been a better time to expand your business, sharpen your skills, and broaden your knowledge.

And if you can’t decide right now, you can always send for the introductory enrollment kit and ing the part presents no significant complications for a competent machinist. From the appearance standpoint, the coupler is an attractive extension of the receiver, and function- Atop this massive rimfire action is a Leupold mount and Sightron scope. ally, it definitely adds strength to the barrel fitting. I would strongly recommend this simple and innovative revision, particularly on the Remington Model 504 rifle.

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