Slings and mounts
While this job might not have the glamour of scope mounting it certainly holds the seed of disaster. I can’t count how many times I have seen a high quality firearm disfigured by off center sling mounts or beautiful wood split and damaged by a screw that was wedged into an improper hole. It reminds me of the golfer that has attempted the 60 foot putt with great care and deliberation but missed and then when the ball is 10 inches from the hole he casually walks up and taps to miss again! He thought the job was so simple that it didn’t need his full effort!
It looks like an easy job. The customer might even add to the illusion with terms like “just pop me a couple holes for a sling”. Might be more accurate if he said “I need two holes with a two step diameter drilled center on a curved sloping surface that has an easily damaged surface”. Bottom line is you won’t get any credit for doing a sling mount job perfect but you sure will catch a lot of grief when it is anything less! Luckily most guns come from the factory with some provisions for a sling these days but the occasional stock still turns up that will need to have sling swivels installed. Understanding the pitfalls of this underrated job might keep you out of a lot of trouble so learn these few tricks of the trade. It just might keep you from waking up nights screaming!
You can do this job with regular tools or save yourself some trouble and buy the specialty tools offered to the trade by some of the gunsmith supply businesses. Drills designed with two diameters that speed up the job will pay for their selves if you are running a full time business. In addition to the drills there are countersinks for the nut required on thin for end installations and drill guides that can help you center up the pilot hole. Brownells sells a tool that resembles a screwdriver. It has a pin that will engage the sling swivel hole and turn in the mounting screw allowing you to keep pressure on the screw to help it resist pulling out of the hole. These tools don’t make the job foolproof but they do speed up the time it takes to do a good job.
It will be the mount for the rear swivel that will cause the most problems. This is normally a simple threaded stud that screws into the stock a couple of inches from the toe. The mount for the forend is normally a 10/32 machine screw with a nut that has to be mounted in the wood below the surface inside the barrel channel to prevent disturbing the accuracy of the rifle. With the forend being relatively straight and flat it is simpler to layout the hole location on center. Examine the threaded portion of the rear stud and you will get a few clues as to what will be working against you. The threads start very abruptly unlike most wood screws. Normally a wood screw is designed to pull itself into soft wood without a pilot hole but one glance at this threaded shaft should be enough to let you know this task would be impossible on a gun stock with this type of threaded screw. This screw is designed to give maximum strength but will require a special pilot hole or it will pull up the wood around the threads before it pulls itself into the hole. This is hard to repair without going to drastic measures so plan ahead to minimize the risk.
The pilot hole is really the critical part of the whole job. It must be large enough to accommodate the shaft or main body of the screw but allow maximum wood for the threads to hold. I usually measure the minimum diameter of the screw with a dial caliper and use a drill only a few thousandths smaller to make sure it is tight but without danger of splitting the stock. If you don’t want to buy a special drill with a two step diameter you will need to drill a second step the diameter of the threads about 1/4 inch deep to prevent the wood pulling up as the leading thread pulls itself into the hole.
Finding the correct location for the rear swivel and making sure it is centered can be a little tricky. Brownell’s sells a neat little tool that is a piece of angle stock that has a drill bushing mounted through the center. In use it is simply pressed against the stock and held square while the hole is drilled. Lacking a drill jig you can hold the stock in a padded vise and level the stock front to rear. Next a center punch is used to mark the location for the hole. Something around 2.5-3 inches from the toe works best. Be alert to any special problems that might cause a problem like the working parts of an adjustable recoil pad or something similar. After the location is marked back up a couple of steps and give it a critical look. If all is well proceed to drill or correct it by moving over and center punching another mark. This is the value of marking the location, you can move it before it is too late! On very thin hollow stocks or synthetics it might require a machine screw and nut to secure.
The front swivel mount is normally a machine screw with nut because the slender forend will could split if the wood screw was wedged into a too tight hole. This mount will also receive the most stress since the gun is carried barrel up and if the sling is use for shooting the bulk of the stress will be on the front. It can also be located with the drill jig or easily centered with measuring using a dial caliper. This hole should be the size of the machine screw and allow it to pass through easily. The recess for the nut can be made with a mini grinder or a counter sink mounted on a drill. Don’t try to use a hand drill with a larger drill because drills are designed to pull themselves into the material and you will probably end up going too deep or pulling up surrounding wood. I like using a drop of thread locker to make sure it never comes out accidentally. This can be disaster since the gun is on the back and hard to grab when it pivots around and the muzzle strikes the floor. If your luck is like mine it won’t happen unless you’re on concrete!
It really doesn’t take that much longer to do a professional job and even though you won’t make a lot of profit it will be another of those crowning touches that make your work a little better than the norm. Do Good Work!
Timothy P. Whealton