Making and Installing An External Hammer Safety

In the case of this Stevens Model 107B shotgun, the normal hammer-rebound safety failed to provide a positive safety for the gun. That is to say, if the hammer, while in the uncocked position, were struck with a loaded round in the chamber, the gun could discharge. Though the possibility of such an occurrence may be unlikely, I considered measures for an added positive safety so the loaded gun could be carried without any possibility of an accidental discharge should the hammer be struck.

I concluded that, in the design of such a safety, it must be fully automatic. It must not interfere with the loading, firing, or unloading of the firearm in any way as it provides a positive, automatic safety mechanism. Designing and Making the Safety I contemplated a few different options for such a safety mechanism, Right top: These parts comprise the automatic-safety attachment for an external hammer. The modified Conetrol scope base (left) has a notch cut to accept the safety arm.

The screw attaches the arm to the scope base, and the arm blocks the hammer. Right bottom: With the scope base mounted to the gun and the safety arm attached, note how the notch in the safety arm blocks the forward movement of the hammer in the uncocked position. and arrived at a principle that was functional and easily adaptable to this particular gun—and could be adapted to many other similar guns.

In mounting the scope to the receiver, I elected to use a pair of Conetrol scope bases and Conetrol horizontal split rings for a most rigid mounting system. The laterally opposing cone screws at the sides of the bases provide an excellent means of rigidly holding each ring assembly in place and offer side-to-side zeroing for the scope as well. In this mounting application, I allowed for the rear scope base to be extended beyond the breechface/barrel juncture by about 3/8-inch—far enough to

attach the pivot point for the new safety arm. The concept of the safety is quite uncomplicated. An arm attached to the slotted tip of the scope base, about 3/4 inch in length, extends over the external striking face of the hammer. The front of the arm has a hole at the end matching the lateral hole drilled in the slotted scope base. I used a 6-32 socket-head screw, and threaded one side of the through-hole in the base for positive attachment.

This safety arm hangs freely and has an underside notch which falls and mates with the square forward face of the hammer. In this position, it allows but a few thousandths’ tolerance between the firing pin and the upper impact surface lip of the hammer. The hammer returns to this precise position following striking of the firing pin each time the gun is fired. It is then in the automatic safe position.

Then, during normal usage, as the hammer is cocked and Left top: With the hammer in the full-cocked position, the safety arm is lowered with its beveled tang below the top of the hammer. Left bottom: As the hammer falls, the upper aspect of the hammer strikes the beveled tang of the safety arm, flipping it upward. The hammer is then free to move into the firing position. the trigger is pulled, there is a means for preventing hammer engagement with the safety.

This is accomplished by the special tang on the rear portion of the safety arm extending out over the hammer. This tang is beveled at its lower rear aspect. As the hammer falls during firing, the upper forward edge of the hammer face engages the beveled part of the arm, flipping it upward. Inertia keeps the arm elevated as the hammer passes beneath the safety notch. After firing, it again falls into its safety position.

The extended arm does not interfere with loading the rifle or removing a partially extracted cartridge from the chamber. Conclusion There are undoubtedly many ways to add an automatic safety to a gun. This method, however, is simplicity itself, and has proven to be a most positive safety feature for this gun. The installation required less than a dollar’s worth of parts and materials, and involved but two hours shop time. ■