Micro-Lapping the Remington Model 700 Recoil Lug

Depending on your customer’s needs and budget, the full blueprinting and accurizing process is not always required’or warranted’with many of today’s modern rifles. Fortunately, however, it’s possible to show a significant improvement in accuracy as a result of some very simple and inexpensive techniques. In preparing Remington Model 700 and 40X rifles for superior accuracy, for example, I direct special attention to recoil-lug precision.

Hav- Top When properly applied and used, the two micro-abrasives shown here do an excellent job of lapping the contact surfaces of the barrel shoulder, receiver face, and both sides of the recoil lug. Bottom J-B Bore Paste is used as a lapping medium.

This material is a very effective bore cleaner, but also serves as a mild abrasive for lapping when properly used. ing removed a number of the factory barrels, I’ve seen less than perfect contact between the barrel shoulder and the recoil lug’as well as an imperfect fit between the receiver face and the recoil lug. Thus, we have a total of four contact surfaces that may lack what I call "micro-precision." This, however, is a condition that can be easily remedied with only the most simple of tools.

A basic, contact-surface test can be performed by applying a machinist’s blue like Dykem to all surfaces, and screwing the barrel on until contact is made. Then, while under a light axial preload, turn the barrel to the receiver back and forth under moderate pressure. A few turns like this will allow a close inspection of each surface. While performing this test, be sure the recoil lug is in the downward position as it would be in the stock. Any other position would not permit a

proper inspection. After a few rotary contacts, carefully inspect the parts for any evidence of uneven contact. There will probably be some. This test will reveal the areas that lack uniformity in surface pressure. While performing this test, always be sure the recoil lug is in the same position front-to-back. It is best to place a small mark on one side. Lapping the Contact Surfaces At this point, we’ll be lapping all four surfaces’t he receiver face, barrel, shoulder, and both recoil-lug surfaces.

This is accomplished by coating both surfaces of the recoil lug with a mild abrasive. For this job, I use J-B Bore Paste (from Brownells), which does an excellent job of micro-lapping. I’ve also used an ultra-mild abrasive that was given to me by Fred Barker, a metallurgist and columnist for Precision Shooting magazine, and gotten equally good results. With the lapping material applied, slip the recoil lug onto the barrel and screw the barrel onto the receiver.

Keep the recoil lug in the downward position on the receiver. I would place the barrel in a padded vise for extra control. With a light contact between the parts and the recoil lug in its normal downward position, rotate the recoil lug about 15 to 20 degrees in each direction from its downward position. I use an adjustable wrench to grasp and move the recoil lug while lapping. Be sure there is a snug fit where the wrench holds the recoil lug.

During the lapping process, the application of controlled torque to the receiver allows a bit more axial pressure between parts. You actually will feel the lapping as a mild abrasive action between parts. Increasing I An adjustable wrench is used to hold and rock the recoil lug while lapping. or decreasing the torque on the receiver allows full control of the lapping. After a few back and forth rotary movements of the recoil lug, it’s time for an inspection. Note carefully how the lapping has affected the parts.

In some cases, this may be all the lapping that is required. On some of the better target rifles on which I’ve worked, a marked difference in bullet point of impact was noted after lapping, along with an equal improvement in accuracy. Even the tiniest fraction of an inch discrepancy at the barrel or receiver contact can represent a full minute-of-angle variance on target impact. Conclusion This simple micro-lapping method can be used on both new barrel installations or on assembled rifles.

It requires little time, and the cost is essentially nothing. Thus far, in using this technique for recoil-lug lapping, I’ve seen accuracy improved significantly in most instances, and in no instance has this process caused a reduction in accuracy.