Quick Detach Sling Mounts In Hollow Synthetic Stocks

Hollow synthetic stocks often do not have enough wall material thickness to reliably mount sling swivels as a wood screw into a conventional wood stock. For those who prefer side mounted rifle slings, the side walls of synthetic butt stocks are often thinner than the bottom edge. Consider commercially available sling mount hardware with hollow stock use.

Uncle Mike’s is one of the most common sources and most conventional sling mount hardware comes with a screw/stud having tapered threads, very similar to a wood screw. This attachment is generally not reliable into hollow synthetic stocks which do not have sufficient wall thickness to support the threads. 3/16" wall thickness is not uncommon on the sides of plastic rifle stocks.

QD (Quick Disconnect) sling mounts use a 1/2" diameter cup shaped sling swivel base which can be epoxy glued into a 1/2" diameter hole in a wood rifle stock, often in combination with a small wood screw through the center of the cup for extra strength. The hole in the wood stock is drilled to depth, resulting in the mounted cup being flush with the surface of the stock. This method isn’t applicable to hollow synthetic stocks either.

For stocks which do offer interior access by removing the butt-plate or recoil pad, previously successful solutions included use of threaded hardware which, when placed inside of the butt stock, provides a place for screws from the outside to thread into. For thinner stocks, fabrication of a custom plate or mounting fixture has proved successful. This article focuses on the QD swivel base and flush mounting the cup in the side of the butt stock.

Most shooters not already familiar with the advantages of side mounting a sling on rifles and shotguns are usually quickly converted. The principles provided here, with adaptation for any sharp curves, will also work to mount a QD swivel base on the bottom edge of a stock. Our solution is diagrammed with the butt stock end view of a Ruger 10/22. All descriptions in this article assume a right handed shooter, with the sling mounted on the left side of the rifle as viewed from the rear of the butt stock.

When the stock is viewed from the rear, the left side will be facing the neck and cheek of a right handed shooter. There are several key points to note that may not be obvious from the drawing. The interference, or press, fit. The 1/2" nominal diameter hole drilled in the left side of the stock wall is intended to be an interference fit. Many plastics which are used for synthetic stocks appear and behave similar to nylon, delrin, polyethylene and similar plastics when they

are machined. That means an exact 1/2" hole will shrink after drilling, often several thousandths smaller than the original size. More rigid synthetic materials like conventional fiberglass may not shrink and might "stretch" to accommodate an interference fit. Because this is a press fit and because of plastic shrinkage do not plan on preliminary "dry fit" tests. Disassembly can be done using a press but the ring grooves cut in the exterior of the cup will catch, at the risk of damaging the stock.

Deburr all edges so as not to catch or grab. Postpone drilling the 1/2" hole in the stock as long as possible to minimize time for shrinkage. Another key point is the socket flush fit at the surface. A spacer the same 1/2" nominal diameter as the sling swivel cup is custom fit to length to provide a flush fit of the cup. Due to the slight contour slope of the stock, the goal is to leave the average of the cup be flush with the stock surface.

It is better to err on the side of leaving a little bit of the cup above the stock surface. Be certain to taper the right end of the spacer. For best mating fit of the spacer to the inside of the stock’s right wall, the end of the spacer should be tapered slightly to match the slope and curvature of the stock interior. This will require an "up" indication mark on the cup and spacer combination, combined with careful attention to orientation at assembly time.

Note that rifle stock shapes may not be uniform or symmetrical. Regardless of the material used, this is not uncommon. Surfaces are often not flat, orthogonal or uniform. The next rifle stock for the same make and model of rifle may be a different size and shape. Mounting The Swivel On to the build. Step one, locate the desired sling swivel location. The location I used is good for the small stock of the Ruger 10/22.

I suggest making preliminary measurements with rifle stock and ruler, used both "square with the world." Shim shin-

gles can hold the stock in a level position and keep it from rocking. Use a Sharpie marker instead of pencil because the marks are more easily removed with solvent. An optional step is to pre-cut a 1/2" round measuring rod. To get the combined length of sling swivel socket and brass spacer it will be necessary to measure inside of the stock. A centering punch slightly under 1/2" diameter and a fine tipped pen work well. A fancier solution is to turn down apiece of brass rod about three inches 1/2" diameter.

The intent is that the Most molded plastic stocks have a mold line that is approximately on center. This mold line can be used to perform a post marking check to confirm that marks on both sides are approximately symmetrical. Wrap apiece of paper over the top of the stock such that the edge of the paper intersects the marked drill points on both sides of the stock. Secure the paper with tape and mark the mold line on top along with both marked drill points. Remove the paper and lay it out on a flat surface.

The distance from center line to each marked drill point on the paper should be about the same. After confirming the marked drill points for the holes to be drilled, mark each with a sharp center punch. Postpone the drilling until you are almost ready to press in the socket/spacer combination. Minimize time for the material to shrink after drilling.

brass rod will fit nicely through the 1/2" nominal hole cut in the left side of the rifle stock. Next, pre-cut and tap the brass spacer. The brass spacer diameter should exactly match the cup diameter. Round stock "mill size" may be larger than nominal 1/2". Turn down the spacer diameter as needed. Make the brass spacer a little bit over length, about 0.060 or so. Drill and tap 10-32 through the entire length. Deburr and taper edges and holes.

The spacer will be final trimmed to length just before shaping the end for stock contour and press fit installation. Custom fit and trim the 10-32 flat head screw to the inside of the cup. Experience with Uncle Mike’s Swivel Base cups shows they work well with #8 machine screws. Use of #10-32 screws as recommended here requires that the screw head be trimmed slightly, both height and diameter, so that absolute full engagement of the male sling swivel insert is achieved.

The male sling swivel insert must go into the cup far enough for the ball detents to fully seat. Otherwise, the sling swivel insert can pull out under load. Confirm that when inserted the male sling swivel has at least some minimal noticeable free play in and out. Now, custom fit and trim the 10-32 screws to length. Using 1/2" nominal length machine screws may not work for a thin stock, such as our project Ruger 10/22. Screw length versus spacer length must be verified and screws shortened accordingly, if needed.

Drill the holes into the rifle stock, using shim shingles and a level to keep the stock "square with the world" while drilling. The holes should be drilled perpendicular to the overall stock shape and not perpendicular to the curved stock surfaces. Study the shape and contour of your stock carefully. Our Ruger stock has a relatively flat surface on the upper half of each side, approximately five degrees from straight up and down.

These nearly flat surfaces, combined with use of an angle meter, helped to shim the stock to be square. Forstner woodworking bits work well in plastic, tending not to wobble and create oversized holes. My Forstner bit measured about 0.003 under 1/2" diameter, perfect for getting an interference press fit. A pilot hole for the Forstner bit is not required. If you do use a pilot hole, keep it very small, much smaller than the centering point of the 1/2" bit. A brad point woodworking bit could be a substitute.

Regular metal cutting drill bits are not recommended this. Masking or painter’s tape can protect the stock surface finish, especially for clamping in a vise. For the small opposite (right) side hole, size it for near zero clearance to 10-32 threads. Start with a small pilot hole followed by a 3/16" drill bit. Trim the brass spacer, shape and bring to overall length. Shape the right end of the brass spacer slightly to approximate the curved contour of the rifle stock interior.

Use the round measuring rod or other round stock to determine the trim-to length of the brass spacer. Account for the curved contour at the brass spacer’s end. Check the overall combined length of the cup and spacer carefully as you don’t have the luxury of a safe dry fit test. Rechamfer the threaded hole in the right end of the spacer if necessary to make it easier to get button head screw started.

After final assembly of the cup and brass spacer and setting with red Loctite (#262 or #271), mark the "up" direction on the edge of the cup and on the flat head screw so that the contoured end of the brass spacer can be properly oriented when the combination is pressed into the rifle stock. Allow the Loctite to cure in case you need to use the flat head screw to rotate the cup and spacer assembly. Press the cup and spacer combination into the stock. Verify mark- American Gunsmithing Association

ings and orient the cup and spacer combination so that the contour on the end of the brass spacer will match the inside contour of the rifle stock. Keep the stock and the end of the cup "square with the world" when pressing. Shim shingles work well to support the stock. If necessary, use an Allen wrench in flat head screw to rotate the cup and spacer combination to align the contoured end of the spacer. Then, re-press the cup and spacer combination to confirm it bottomed.

Screw in the 10-32 button head screw on the right side using blue Loctite (#242.) If the hole in the brass spacer does not line up exactly with the small hole in the right side of the stock, use the non pointed end of a centering punch to rock the cup and spacer combination until the hole in the brass spacer exactly aligns with the hole in the rifle stock. Use an Allen wrench in the flat head screw to hold the cup and spacer combination while tightening the button head screw. We’re finished.

Expect that the edge surface of the cup will not be uniformly even with the surface of the stock, due to slope and curvature of the stock. Alternative Method There is an alternative method to this build with no screw used on the right side of the stock. Although the small button head screw on the right side of the stock, as used in the above method, is minimally intrusive, some shooters may want to eliminate the need for the screw for appearance purposes.

A solution using glue can be used but the suitability and ability of the glue used to reliably adhere to the synthetic material (plastic) is a big governing factor. Your results may vary. Given the general "slippery" nature of some plastic materials used in synthetic stocks, this author cannot vouch for or guarantee any specific plastic glue. The reader will need to verify that the glue used will adhere to the stock material.

However, Devcon Plastic Welder II (devcon.com, is at the top or our list as a recommendation to try. Try for yourself and confirm the ability of this product to adhere to your stock by gluing to a non-visible portion of the stock. After your confirmation, you may grind off the glued-on experiment. Almost all steps to perform for the glued-in solution are the same as described above with the following exceptions.

First, do not drill the small hole in the opposite (right) side of the stock for the 10-32 button head screw. Threading the brass spacer all the way through is still recommended. The threaded hole will offer a place for the plastic glue to fill into. Second, "rough up" the surfaces where the glue will adhere to, including the inside of the rifle stock (right side) where the brass spacer will seat, the right end of the brass spacer and the right 1/4" of brass spacer.

Cut small groves in the right end of the brass spacer. Third, just prior to pressing the cup and spacer combination into the stock, apply a liberal amount of plastic glue to the right inside wall of the stock where the brass fitting will "seat" against the right wall. Note that the glued-in solution offers no opportunity for re-work. A glob of glue on the end of the brass spacer would almost certainly prevent removal of the cup and spacer combination. What happens if a the glue joint fails?

Worst case, the sling mount could pull completely out of the butt stock at the most inopportune time, allowing the weapon to fall to the ground or to an unsafe position. The press fit may reduce the risk somewhat. Note that the outside of the sling swivel cup has three groves cut into the outside of the cup. These grooves are designed to catch and hold for a glued-in installation into a wood stock.

Based on my experience with the press fit of the cup into a plastic stock during removal, when pressing a cup and spacer combination out of a stock the grooves on the outside of the cup tend to catch very firmly on the wall of the rifle stock and make removal of the cup and spacer combination difficult. The groves caught so firmly that we were surprised this removal did not break the plastic stock.

Based upon this experience, even if the glue joint fails, pulling the sling swivel out of the stock could still be difficult. That said, for reliability, I still recommend using a button head screw on the opposite side outside of the stock to capture and secure the cup and spacer combination. Safety Safety starts with common sense. Always confirm and reconfirm a cleared weapon every time you begin to handle or work with it.

The reader is expected to have an indepth working knowledge of shop practices, including gunsmithing experience. All of the usual disclaimers apply. As we have no control over the execution of these processes, we can assume no liability. Your results may vary. Materials List Berryman B-12 Chemtool (# 0117), available at good auto supply stores, is great for pre-glue cleaning and removal of pen markings. It will attack most wood finishes and many plastics.

Test on an out of sight sample first (berrymanproducts.com, 10-32 x 1/2" Stainless Button Head Screw (length depends on your stock) and 10-32 x 1/2" Stainless Flat Head Screw, Allen socket head (may substitute Phillips head.) I get mine from South Coast Stainless (SouthCoastStainless.com, Uncle Mike’s QD Push Button Detachable Swivels #1011-2 (unclemikes.com, Devcon Plastic Welder II for the glue-in solution (devcon.com, G