Dealing with Screwed-Up Screws

One of the more perplexing aspects of gun repair is dealing with screws that somebody else has messed up. Whether the screw has rusted in place, has been stripped, had the head twisted off or chewed up, or is just plain missing, an annoyance like this will eventually find its way to your bench. Once you learn how to avoid producing these problems if they don’t already exist, and you see a few techniques used to deal with the problems if they do, dealing with screwed-up screws will no longer be a major headache.

Driver Bits The most common styles of driver bits we use in our work are the flat blade, hex, cross, and Torx styles. We have no control over the manufacture of driver bits and the tolerances that are allowed during the machining process, nor do we have anything to say about the tolerances allowed by the screw manufacturers. All we can do is deal as best we can with what we get, and try to maintain the fit between the driver bit and the socket.

Screws with a single slot are most often used on firearms, and these seem to get the most abuse—usually from gun owners who use a tapered flat-blade driver bit. As the screw is tightened into place, because of its shape the tapered blade creates a condition referred to as "cam-out." A driver bit with flat sides that fits the slot as closely as possible for width and diameter will virtually eliminate cam-out or slippage. Screws manufactured with hex-socket heads require a hexwrench to turn the fastener into place.

These screws are most often seen on scope bases and rings, and are occasionally used to draw a barreled action into the stock. Under ideal conditions, hex-wrenches have a 60-degree drive angle. When tolerances become minimal on the hex-key and maximum in the hex-socket that receives the wrench, ugly things can happen. The 60-degree driving angle is lessened, and the hex-key turns the screw into place more on the points of the wrench where the sides intersect (see Figure 1).

This will cause the hex-key to start rounding over and, in an extreme condition, the wrench will round the hex walls in the screw. It’s best to look over your hex-key to see that the corners are still sharp; if there are signs of rounding, either grind the end back to where corners are once again crisp or else replace it. Figure 1.

Standard Key Keep in mind that the depth to which the hex-key fits into the fastener socket can be a minimum of only .064 inch according to ASME B18.3-1998 (American Society of Manufacturing Engineers), so if the corners of the wrench begin to round over the wrench will begin to round the walls of the fastener socket. A hex-head screw with a hole that’s become rounded will be a factor to contend with.

Leupold has been shipping the Torx-style fastener for quite some time with their scope bases and rings—along with the correct size wrench. Brownells has a replacement scope-base and ring-screw kit that comes with driver bits for this style fastener. The Torx-style fastener has multiple 15-degree driving angles which are less prone to rounding over, and allow tightening of the screw into place more securely. The cross-style of screw socket is seen occasionally on buttplate and grip-cap screws.

These are usually are not much of a problem as long as the correct size bit is used. Most common sizes of cross-screw driver bits are the #0, #1 and #2. The tip

of the driver has a forward taper, so if some forward pressure is used to keep the driver bit in place the likelihood of cam-out is slight. Rusted and Busted When you’re dealing with an obviously neglected firearm you’ll often notice rust on the exterior. If rust is present on the outside, you can bet you’ll find rust on the inside. When screws will not easily turn during takedown and there are visible signs that the screw could be frozen in place by rust, assume that it is.

A product that has helped me to free up screws rusted in place is called Kroil. I prefer the Aero Kroil, because I can direct the spray into areas that look as though they need it. This stuff is advertised as "The Oil That Creeps" and the description on the can says it will find its way into openings as small as one millionth of an inch. It’s the best penetrating oil I’ve ever used, and has never removed or harmed any gun-metal finish.

If a screw remains stuck in place after the Kroil treatment and an overnight soaking, I’ll use my heat gun on the frozen-in-place screw. Because we never know if somebody put thread locker of some sort in the threads, the heat will help to soften the thread locker and loosen those Then they can be polished and blued. threads —or maybe even increase the opening to two millionths of an inch so that the Kroil can flow to the rescue.

After this treatment, the screw will normally come out with a properly fitted driver bit. Another trick to try is inserting a driver bit that fits the slot as closely as possible, and giving the back end of the bit a sharp smack with a hammer. This shocking action may move the screw down a bit and allow the penetrating oil to creep a little further in to help loosen any stubborn rust adhesion.

The type of screws used on firearms require more of a function fit rather than a class or interference-type fit, so there is some slight play between the screw and the receiving thread. When tightened, gun screws pull up into place in the receiving threads leaving any tolerance that may be there at the bottom side of the thread. This often makes the screw susceptible to the "shock treatment." Kroil can also be used to clean carbon-fouled barrels.

It will get in between the fouling and barrel metal to loosen the hardened crud for removal, so this stuff is handy to have around. Broken screws can make the hair on the back of your neck stand to attention. Whether the head has been twisted off completely or half the head has walked off the job, the approach to removal is pretty much the same; obviously, we need to remove what’s left of the screw so it can be replaced.

An example screws with stripped hex-sockets that can normally be easily removed are those on scope bases. The idea here would be to remove all the screws that can be removed with a well-fitting hex wrench, leaving the stripped-socket

screw for last. Measure the outside diameter of the socket head on one of those screws you have removed, and then choose a drill bit the next size smaller than this dimension. Set the barreled action up in your drill press so that it is tightly held with the head of the base screw as parallel to the drill bit as possible. Center the drill in the hex socket and feed the drill into the socket slowly until the head is drilled away. The base should then lift off the receiver leaving a threaded nub of the screw.

Carefully clamp a pair of locking pliers on what’s left of the screw and turn it out. The heat from drilling will usually soften any thread locker that is captured in the screw threads, but if there was a delay in getting the pliers in place, you may need to apply some heat from a heat gun to re-soften the thread locker. Slotted screw heads can be a bit more difficult to remove if half the screw head has broken away or if the slot is so chewed up that a flat-sided bit will not do the job.

In these cases, I use a #1 screw extractor, commonly called an "easy-out." This tool has a left-hand fluted twist that, when turned with a tap wrench, digs into the side walls of a hole previously drilled into the broken screw head. The screw head is prepared for the easy-out by first drilling a starter hole with the smallest center drill you can get your hands on. The one I use is a #11 that has a main body diameter of .125 inch.

The barreled action is set up in the drill press as previously mentioned, and this tiny center drill is centered over the screw slot. The idea behind this drill is to get it cutting as close to the exact center of the broken screw as possible, as this is basically a starter drill for a 5/64-inch-diameter drill. The reason to use the center drill is because it’s short and stiff and will not wander around on your work the way a longer, small-diameter twist drill would tend to do.

Once you have the center of the screw spotted with the center drill, the 5/64 drill will follow the starter hole until you drill to a depth of 1/16 inch or so. Since the easy-out has a tapered configuration, the very end of it will only go into the 5/64-diameter hole a little bit. I normally give the top end of the easy-out a couple of taps with a 4-ounce hammer to get it seated in place.

Using a tap wrench clamped tightly onto the end of the easy-out and turning the tap wrench counter-clockwise will usually bring the screw out of place and allow you to breathe easily. Buggered and Battered We’ve all seen what can happen to screw slots when a poorly fitting, tapered flat-blade screwdriver has been used on them. The slot can get twisted out of shape, and the top of the slot often becomes rolled over. The simplest solution here would be to replace the screw.

In many cases, replacement screws are not available and in other cases the owner wants to have the firearm’s originality retained, so we would need a screw head that looks as close as we can get to the original. To return a screw with a chewedup head back to like-new condition, a plate must to be made that supports the back face of the screw opposite the slot side. Drill a hole in a mild steel plate at least 1/2-inch thick, so that the outside diameter of the screw threads will fit through the hole.

Chamfer that hole or counterbore it so that the screw head will nestle in place. The next tools you’ll need area flat-sided needle file and a small ball-peen hammer. The idea here is to strike the rolled-over edges of the slot with a few taps from your hammer while rolling the hammer in a semi-circle toward the slot—kind of like scooping ice cream. The attempt is to cold-form the rolled-over slot metal back into place, and then to use the needle file to straighten out the side walls of the slot.

After you get the hang of this, it becomes much easier to do than it is to explain. Obviously, this procedure will only

work with screw slots that are only slightly damaged. If the edges of the slot have been chipped away, it’s definitely time to replace that screw. If you’ve ever tried to find single-slot, oval-head buttplate replacement screws, you already know how difficult that can be. Traditional steel butt-plates, whether flat or curved, normally use oval-head, slotted screws to fasten the buttplate to the back face of the stock. These screws are quite often found to be chewed up, broken, rusted, or missing.

Substitute screws can be found, but most often they are made of brass, stainless steel, or zinc-plated mild steel. You will also find replacement screws that have the cross-type (Phillips) head, but if you’re striving to maintain the look of originality, those just won’t do. I stumbled onto a technique for using oval-head mild-steel screws that are zinc plated. Many times these screws can be used to replace buggered up originals, but they just don’t look right with the shiny zinc plating.

While trying to find a quick bluing solution that would cover the zinc plating, I found that Birchwood Casey’s brass black will actually remove the zinc plating. I use an empty 35mm film canister, filled about three-quarters full with the brass black, and drop the zinc-plated screws into the solution. Put the lid on and swish the solution around so that the screws get completely covered. After about five minutes, pull out the screws and clean them off with a paper towel and look for any remaining zinc plating.

If you see any of the plating remaining on the screws, give them another quick swish-around in the brass black solution. These screws will look nice and black when they come out of the solution, but the finish will not stay on the screws permanently. Don’t leave the screws in the brass black too long. During my experiments with this process, I left a couple of screws in the solution overnight and it began to eat the base metal and ruined the screws.

As long as you remove them from the solution in time, you’ll have screws that can be polished and blued by whatever means you prefer—and for a very cheap price. Missing Screws Sometime we come across a firearm with a missing screw and need a means to determine the thread dimensions so it can be replaced.

This can be a challenge when you’re dealing with an obsolete or foreign firearm. "Facsimile" is a product I’ve used many times in the past where no blueprints were available and parts needed to be reverse-engineered so that I could get a print drawn up and produce the parts. I now use this product to make castings of threads, and it also works great for making very accurate chamber/throat castings. If you’re interested in acquiring the Facsimile kit, contact Flexbar Machine Corp.

Islandia, NY 11749; www. flex bar.com). When I come across a firearm with a missing screw and don’t have any information at hand concerning the screw size, I’ll make a casting of the receiving hole with Facsimile. This quick-setting compound is very simple to use, and provides a molded clone of the missing screw thread. There are several preparatory steps before the compound is poured into place. Adam needs to be placed on the off-side of a throughhole thread.

This can beapiece of tape or modeling clay—anything to keep the compound from flowing through when in the liquid form. The threads in the receiver then need to be coated with the release agent that is provided in the kit. I then use an old cartridge case as an extension on the outside of the receiver with modeling clay packed around the area where the case meets the receiver face to prevent leakage.

The Facsimile powder is then mixed with the liquid catalyst until you achieve a smooth consistency that flows easily in one of the small paper cups provided with the kit. This mixture is then poured through the cartridge case slowly so that the compound can fill the threads. It takes 10 minutes or so for the thin compound to harden up to the point where the cartridge case extension can be turned out with the perfectly replicated threads.

All you need to do now is to measure the outside diameter of the threads with a micrometer and the number of threads per inch with a thread-pitch gauge, and then you can begin the lathe work. Conclusions With the techniques outlined above, removing troublesome screws doesn’t need to be an arduous affair. Nevertheless, finding replacement screws can mean spending a lot of time on the phone with parts brokers to see if they have what you need—if they even know what part you’re referring to.

Most often the phone bill will mount up and it’s very difficult to tack on the cost of a replacement screw to the bill. With tricks like using Facsimile and custom-blued hardware-store screws, you can keep these costs to a reasonable level. ■