Fine Gunmaking

A few months ago on an Internet forum a fellow asked, “What are the screws in the sides of the fences for?” It was a simple and straightforward question, and the short, sweet answer would be: “To hold the striker disks in place.” The longer answer deals with strikers, disks and the tiny hole you might never have noticed in the above-mentioned retaining screw.
    Basically, there are two types of double-gun strikers, or firing pins: those common to boxlock guns that are integral with the hammer, and those common to sidelock guns that are separate parts enclosed in the action body and struck by the hammer. Sidelock strikers are often held in the action by bushings or disks threaded into the breech face and are known as “disk-set strikers.” (As always with double guns, there are no absolutes, and there are boxlock guns with disk-set and solid strikers; and although I have not seen such, I’m sure there are sidelocks with solid hammers/strikers.)
    Referring to the top photo, I’ll define the various parts of a disk-set-striker assembly. On the extreme right is the three-diameter striker, or firing pin; below that is the striker-disk retaining screw; and to the left is the striker disk with the firing-pin retractor spring in place. For convenience, I will call them the firing pin, retaining screw, disk and spring.
    Looking at the action body in the top photo, it’s easy to see one striker disk installed in the breech face and the threaded hole to the right where one has been removed. In the lower fence the hole for the retaining screw is visible. Looking a bit closer at the removed disk, you can see the hole in the threaded portion where the unthreaded end of the retaining screw locks it in place. Also note that the disk, spring and firing-pin holes in the action body are drilled at the upward angle of the firing pin. The firing-pin angle is most easily recognized by the angled face of the disk.
    The bottom photo shows the parts up close along with three variations of disk-removal tools. On the right are two screwdrivers ground to fit the pin holes at the correct spacing. At the upper left is an adjustable disk-removal tool (available from Brownells) with an eccentric cam to vary the distance between the pins to fit different disks. Unfortunately the tool’s pins are too large to fit this particular disk. Any ’smith versed in double-gun repair will have many specially ground disk-removal tools and be ready to make another when an oddball gun comes into the shop.
    Now is a good time to caution against home removal of disk-set strikers. I often have found them to be tightly fit if not battered into place by repeated cartridge percussion. The pin holes are as easy to bugger as the hair-thin screw slots on “best” Italian guns. The disk face, not being square to the breech face, adds to the complication of removal. And if you forget to first remove the retaining screws—which are likely to have very thin slots—from the side of the action, you will remember when the disks refuse to come out and the breech face is well scarred. (Or your gunsmith will recognize exactly what you tried to do when the gun winds up in his shop.) Also the retaining screws often are engraved with the continuation of scrollwork that is easily damaged and must be perfectly realigned on reassembly. So attempt removal at your own peril!
    Also in the bottom photo you can see a hole in the end of the firing-pin retaining screw. The screw is actually bored all the way through with a hole that is so small (.040") that the screw slot on the outside covers it up. This hole is for venting any gas that might leak from a blown primer or ruptured cartridge case. In English gunmaker vernacular this screw is know as the “vent pin,” because “pin” is British for machine screw and it vents the breech. Another method of venting the breech was accomplished with a small groove machined into the breech face from the firing-pin hole outward to the edge of the fence that would allow escaping gases to bleed off away from the shooter. In a gun so equipped, these are easy to see when viewing the breech face. More on venting in a moment.
    The mechanical operation is simple: The hammer, or tumbler, in the lock strikes the firing pin, which transfers energy to fire the cartridge primer. The spring retracts the firing pin to keep it from sticking in the primer and locking the gun shut. Boxlocks (most often) have solid pins, because the hammer easily can be aligned with a centered hole in the breech face, and the cocking lever retracts the firing pin when the gun is opened. Because sidelocks can be removed easily from the gun, it is more convenient and compact to separate the firing pins and install them in the action body. These disk-set strikers also make it relatively easy to remove and replace the firing pins.
    Firing pins do break and look to be easy enough to make and replace. They are simply three-diameter pins with a rounded tip on the ignition end, a shoulder for the spring to stop against, and a larger-diameter rear that the tumbler strikes. When fabricating a new pin, it is critical that the length of the front end be measured to the correct firing-pin protrusion—the length of the pin that protrudes beyond the breech face at the hammer’s fall. Firing pins should be made from steel that can be hardened and selectively tempered, because the front end can’t be brittle or it will break and the back end must be hard enough to resist mushrooming from repeated blows of the hammer. If the back end mushrooms because the steel is too soft, the pin will be extremely difficult to remove from the action.
    The practice of venting the breech goes back to the pre-flintlock era. I surmise that there is a direct connection between flintlock vents and the tiny vent hole found in a modern striker-disk retaining screw or vent pin—though as with much in the history of firearms development, there is no factual proof.
    In order to fire a flintlock gun, the vent, or touchhole, was a tiny hole in the breech next to the lock’s flashpan that allowed sparks to flash through to the powder charge when the priming pan ignited. In later percussion guns it is not unusual to see platinum “blow-out plugs in the side of the gun’s breech that theoretically would “blow out” in the case of excessive breech pressure. Many of these platinum plugs have a tiny hole through them and, when fired, a squirt of smoke escapes from the hole. So putting a screw into the side of the breech of a gun has much historic precedent, and adding a hole through the retaining screw seems a logical step in double-gun evolution.
    And that is the long answer to the question: “What are the small screws in the sides of the fences for?”

Autographed copies of Steven Dodd Hughes’s books, Fine Gunmaking; Double Shotguns and Double Guns and Custom Gunsmithing, are available for $48 each postpaid from the author, PO Box 545, Livingston, MT 59047.