One of the things some gun owners—engineers or fairly well-educated hobbyists who have a good grasp of mechanical things—ask about is how to handle the different kinds of pins in their guns. Particularly, they often want to know if their punches are the right ones, or if they can use a slightly different one without damaging their pins. Gunsmiths who have worked for years with different kinds of pins take the varied shapes, uses, and special punches needed to work on these items for granted, but there’s a few intricacies about dealing with them that aren’t common knowledge among either customers or ‘smiths.
Below, we will discuss some of the more frequently found pins, their uses, the special punches for them, and then how to use the pins. It is also helpful to know how to modify pins without spoiling their usefulness, and you’ll benefit from knowing several methods of making them stay in place.
The Straight-Ended Pin
The straight-ended pin is the most commonly used pin. Its shape is strictly cylindrical and is usually annealed (unhardened). It may be made of almost any material, but it is usually carbon steel in most firearms. Its fit can be either slip-fit or interference-fit, depending upon the use of the pin. But even when it is used as a slave pin, it’s still called a straight pin.
Standard pin punches, drift punches, and small steel rods all serve well in dealing with straight pins. There are times when just a piece of rod, a nail, or a small screwdriver will suffice in removing a pin. Be that as it may, it is always better to use the most impressive punch you can when the owner is looking on. The impression of using the right punch is usually as important, if not more so, than the results achieved with it.
Dowel pins are usually hardened steel with slightly chamfered ends that aid in starting the pins into holes. The ends are not usually finished to a smooth surface, but the sides of the cylindrical body of the pins are most often ground to a very fine finish. With their hardness, any irregularity in the sides would broach metal along with the pin when it was installed, causing galling and sticking when the pin needs to be removed.
The distinctions between dowel pins and straight pins is somewhat blurred, as there are often dowel pins with only one end chamfered and also some straight pins which have had the ends deburred by blending the sharp edges away. As with straight pins, dowel pins respond well to being driven with pin punches and drift punches. The choice of punch will be determined by the tenacity of the pin in its hole. Drift punches are stronger than most pin punches, and tend to be used with more force; therefore, they will likely leave scarred pin ends. This can play havoc with good-looking pins in highly visible places.
Roll pins, or spring pins, are commonly used where two or more pieces are to be held together, but not pivoting in relation to each other. The pins are split longitudinally, with the edges of the split opening sticking out from the diameter of the pin. This gives two edges that bite into the part’s hole, keeping the pin in place. They are usually tempered blue-violet like a spring and made of spring steel, hence the name spring pin. The hole forces the two edges of the split in, causing the pin to achieve a round shape with quite a bit of outward force against the hole’s walls. With these edges biting into the walls, seldom do roll pins come out without some persuasion.
Still, I have embellished their holding power by scoring their edges with diagonal pliers. This should be done only with pins that are to remain in the holes and are not in a place where the edges of the hole will show. I do this when the hole has become too large for the pin and the pin’s slit edges cannot be forced wider with a sharp wood chisel.
Roll pins are used almost everywhere pins can be found and have good holding power and strength. They should not, however, be used where there would be something turning on the pin. The lengthwise split would quickly enlarge the hole in the rotating piece and render it useless.
When using them, they should be started into their holes with a roll-pin-starting punch. In spite of the obvious naming, it is pretty hard to find something like this in the local hardware store. I get mine from Brownells stock and find they are much better and safer than trying to hold the pin with a pair of long-nosed pliers while driving the pin into the hold. This punch is identified by the hole in its end, into which the roll pin is placed. The punch makes it easy to hold the pin in line with the hole and drive it far enough in to establish the direction it will need to go. The roll-pin-starting punch need not be limited to just roll pins, but one must realize its limitations and not use it to force tight, solid pins into a hole with a healthy interference fit. This will just break a good punch.
As soon as the pin has started, usually about one fourth of its length, it is safe to change to the other type of roll-pin punch. I usually continue with the starting punch, though, until the punch nears the top surface of the hole. There is almost no chance of slipping the punch off the pin as there would be with any other type of punch.
The main roll-pin punch is used in seating the roll pin and in driving it out of the hole. This punch is identified by its ball right in the middle of the face of what looks like a regular drift punch. It is this punch that gets abused the most in my shop. I have many friends and students using my tools, and in their enthusiasm to work on their own guns, they often don’t notice the little ball on the end and flatten it out against a straight-ended pin. Accordingly, I keep these two roll-pin punches in plastic .22 cartridge boxes with a large “NO!” printed on the top. This has been effective in keeping the punches from being damaged.
Spiral pins, the most popular brand-name being named “Spirol” pin, are pins made of rolled-up spring-steel flat stock that takes on a spiraled look when viewed from the end. For the pin to compress, it must have enough force exerted against it in an inward radial direction to overcome the friction of the stock rubbing against itself when the spiral is tightened. They are very tough pins and can be used for some rotational situations without their hurting the hole they are in. They are hard to get started, but drive well when they are in the hole over one quarter of their length. They are somewhat finicky about having the right-sized hole. They do nothing that a straight pin won’t, but they retain their position well if they are put in a hole near the right size.
They should be installed and removed in the same manner as roll pins and with the same punches. You may need to use a smaller punch than the outside diameter suggests, because different pins will have more spirals depending upon how much holding power they possess.
Tapered pins are just straight pins with one end smaller than the other. They are used to drive gears and locate parts, but never to have an object rotate about them. Tapered pins are designed to be installed into tapered holes and should always have a small through-hole in the bottom of their receiving hole to facilitate their removal. They most always have domed ends, but the domes vary so much that there are no punch sets that I know of for these pins. Because they are hardened, use standard pin or drift punches to install or remove them.
These pins have ends that are hemispherical and polished, as they are usually ball ended for aesthetic reasons. Few things look as bad as ball-end pins that have been abused by being driven with other than cup-ended punches. As far as destroying a gun’s cosmetics, marred ball-end springs rank right up there with boogered-up screw-head slots on firearms.
One of the most common uses of this type of pin would have to be the barrel pin on Smith & Wesson pistols. It takes a very small cupped-head punch to drive these small pins out without either flattening the ball end or scoring the receiver around the pin’s hole.
Grooved pins are the invention of Groov-Pin Corporation, hence their name, but they are manufactured by a number of companies.
These pins are generally dowel pin-like in nature, with some chiseled grooves around them to raise up ribs that bite into the hole’s sides. The raised lands are sharp and can be either at 90- or 120-degree intervals around the pin. The splines, lands, or whatever a particular company calls them, are from one quarter, one half, or up to the full length of the pin. The lands are formed by impact—not rolling as are the splines of splined pins.
Grooved pins are usually tapered on the ends and can be easily driven with a hammer. I choose to refer to my hammers as high-speed presses, as this draws more sympathy when I happen to compress the end of my thumb. Work with pins and you’ll, sooner or later, need the euphemism to save your pride.
Splined pins are the pins with straight or crisscross grooves that are rolled into the metal in a continuous pattern. The rolling causes the metal to be raised between the grooves by almost the same height as the grooves are in depth. This displacing of the metal cold-works the grain structure and hardens it to some degree, making for great holding power. The pins are installed and removed with pin punches like the straight pins and are nearly always made of high-carbon steel, but are not hardened. They make very good pivot pins for triggers, hammers, and other gun parts, but they are usually confined to the lower-priced guns. They do not stand much removal and re-installation, because the splines cut into the hole are either destroyed after several installations or they are deepened so that the pin goes farther into the hole than it was intended.
When they find splined pins on a handgun, many consumers want to throw the gun away. But there is nothing wrong with these pins, as their use on military weapons suggests: for instance, the M-16 contains them. They should be put in by hand, and the ‘smith should remove them by bending the bent end straight and pulling the ring-shaped head away from the hole. Due to their very nature, splined pins must be driven in with quite some force, or they will not do what they are designed to do. That is, they must displace some metal, cutting grooves into which the raised splines will stick. Start them with a hammer and only change to a drift punch when they are mostly into the hole.
Cotter, or detent, pins are so reliable and low cost that they are used extensively on airplanes. Most cotter pins are made of a fairly soft steel, but there are some stainless, spring steel, and brass ones to be found. I never replace those made of spring steel or nonferrous metals.
One of the guns which uses detent pins is the MAC 10. Its front pin is either a hollow pin with a barbed pin to retain it, or the detent pin of recent years. The hollow pin is just like a hollow rivet with a hole for the barb of the retaining pin. The latest MACs have used detent pins, as they are more easy for the uninitiated to use. You just push until it is installed and pull until it is removed.
The ball is really a plunger, as the detent is the dent that the ball was intended to fall into. In the case of the MACs, the plunger ball pops out just outside of the hole and the universe acts like the detent (dent). The ball is a hardened bearing with a coil spring under it, and the top of the hole is staked to retain the ball and spring. I rate these pins pretty high, although they ensure that there will be some of the pin sticking out farther than I would like for it to. This is the reason the pin is usually relegated to the military style of weapon.
Another pin in this family, the hairpin cotter is familiar to those who have worked on cars. They are fairly reliable. They are used both in grooves around a pin, and with a hole in the pin and the straight leg sticking through the hole.
A second cousin of the hairpin cotter is that even more active pin with the curved leg on both sides. This one almost always is mounted in a groove cut around a shaft or pin. Shadetree mechanics call them “Jesus Clips,” for the number of times they have had to say, “Jesus, where’d that sucker go?” If you take them off with a pair of long-nosed pliers, instead of prying them off with a screwdriver, you can control them better.
Knurled pins are soft straight pins that have been rolled with knurling rollers to offset metal into either straight or diamond-shaped lands or raised points. These pins are usually hardened after the knurling so that their barbs can bite into hard metals for retention in the hole. The knurled area may be the full length or even as little as one quarter of the length of the pin.
The clevis pin is quite handy, and it is usually used in conjunction with cotter pins or hairpin cotters. They have a round head with radiused edges and a countersunk hole in the shaft near the end. The use of the clevis pin is about the same as the detent pin; it is more suited to military looks than the sleek look preferred on consumer firearms.
Sometimes, a clevis-like pin is used with its head in a counterbore and the proximity of another part retaining it. This is true on some models of lever-action rifles. It is a most useful type of pin, and, used correctly, is practically infallible. They should not take any amount of tapping or hammering to remove them, just a stiff wire or welding rod in most cases. The most famous cupped-end pin found on firearms would have to be the mainspring housing pin on the 1911 automatic pistol. It is really a combination of a ball-end and a cupped-end pin, as it is meant to be driven in one side and out the other. The cupped end is usually found on the left side of this weapon but functions equally as well on either side. This pin has a circumferential groove in the middle that serves as a retainer when the mainspring’s lower plunger point is in it. I rarely run into other uses for it.
John Browning used it on the 1911 because a good military weapon should be able to be dismantled with only a cartridge. But, you say, the .45 ACP has a round nose? Well, nobody’s perfect.
I use an ordinary pin punch to remove the 1911 mainspring housing pin, but I only push on the punch and don’t hammer the pin out. When the gun is a pristine, glossy-blue new one, I use a brass punch with a ball-shaped end to push the pin past the mainspring axis. This should always be done with the hammer in the uncocked position to minimize the pressure on the retaining pin when you are trying to remove it.
The other pin on the 1911’s mainspring housing is the flathead retaining pin that holds the mainspring and its end in the housing. It is a small pin that is straight on one end and has a head like a slotless flathead screw. The head is designed to go into a countersunk hole in the front side of the mainspring housing. The 1911 sear pin and hammer pin are similar, but with a much shallower angle to the countersunk head. The have such a slight head that it is difficult to see if you’re tired or in a hurry. These should be slip-fit and require no installation or removal tools, while the mainspring plunger retaining pin will usually take a pin punch to push the pin out while the plunger is depressed.
Other Firing Pin Tips
There must be some cases where you shouldn’t use lubrication on a pin when you’re reinstalling it, but I cannot think of one. I prefer to use some good oil with a few drops of STP in it so that the oil will stay on the pin no matter how long the firearm is inactive or how much pressure I must use to install the pin.
I highly recommend the use of a Dremel cutoff wheel when cutting pins, because it only produces a small amount of heat to change the temper of a pin, and it can cut any steel pin, no matter how hard it is. Cutting pins with diagonal pliers or bolt cutters calls for a serious secondary operation to remove the squashed end. The cutoff wheel cuts with a good square end which can easily be blended smooth with a Scotchbrite wheel in a few seconds.
Most pins are removed with the punches that put them in, only there are some cases where a pin may be above the surface and can be “rolled out” with end-cutting pliers. I find this a good way to remove pins that have been driven into a blind hole, but is still sticking out enough to be grabbed with the end cutters.
There are several good ways to make pins stay where you put them. They can be bent slightly so they will exert pressure on both ends of the hole, or the end(s) can be flattened with a hard hammer, or they can be staked with a centerpunch. I also use medium-torque thread-locking compound, such as Locktite, Staylok, or other products to hold them fast. Which method you use should be dictated by the situation and how visible the pin is. It would not do to flatten the end of a high-priced pistol’s hammer pin if it is prominently in view.
Some pin situations call for setscrews in a perpendicular hole to lock the pin in place. This can also be accomplished with the top of the pin’s hole being threaded for a locking screw.
Along with the bending and egg-shaping the pins, you will run into cases where you will have to straighten out bent pins. I just roll them on a flat steel surface while hammering them with a smooth-faced hammer. Be aware that this will often cause the length of the pin to increase. This can be used on purpose to lengthen pins, as well as scoring them with diagonal pliers.
As long as the pin is out of view, and there isn’t a bending force on it, there are many ways you can get away with tightening, stretching, and locking them into their holes. Some are better left to be done when the proud owner isn’t there to see, as most nontechnical types don’t understand the existence of tolerances and the growth of holes when exposed to stress. If there is a persistent owner in view, I’d suggest the use of a thread-locking compound, even though this isn’t usually as secure as the mechanical methods of securing pins.