Custom Firing Pin For A Stevens Single Shot Rifle

Tasked with repairing an old Stevens single shot, I could not locate a needed firing pin replacement and decided to make one. The diameter of the main firing pin body is 0.227 inches, so I elected to use a section of 15/64 (0.234) inch drill bit shank for the part. The drill bit shank was of ideal hardness without being brittle and was easily machined with carbon steel tool bits. The drill bit was chucked in the lathe as the shank and firing pin end were turned to specification before removing.

The firing pin hole was carefully measured and found to be 0.092 inch. It is important that the firing pin fit properly with as little clearance as 234") down to 0.227" diameter. The piece is completed before removing it from the lathe chuck. The firing pin nose point radius is clearly shown here with its halfcircle configuration. possible to avoid gas or particle blow back as a result of excessive clearance here. For this reason the firing pin should obturate the hole in the breech face.

The protrusion of the firing pin nose, beyond the breech face, was also measured and total firing pin length was found to be 0.188 inch. Forward travel of the firing pin is stopped as the spherical shaped main body bottoms out in the firing pin well. Proper radius is applied at this juncture of the firing pin body during the machining operation. The firing pin should extend approximately 0.075 inch beyond the breech face on firing and must be checked accordingly.

Having determined firing pin length, the nose must be properly shaped for efficient primer function. There remains different thinking in the area of firing pin nose configuration. Assuming the firing pin spring or hammer spring delivers enough impact to fully crush the primer wall against the anvil, both the elliptical (oval), or spherical (round) nose will accomplish efficient primer ignition. However, one must guard against too pointed a nose on the firing pin or primer wall perforation may ensue.

This is particularly true where high cartridge chamber pressures may exist. Conversely, the more spherical firing pin nose tends to more fully close off the firing pin hole in the breech

face at full impact and during peak breech pressure. Whereas the oval or more pointed firing pin nose would tend to allow the primer wall to extrude more along the firing pin nose and along the inner wall of the firing pin hole in the breech face. This may account for some of those perforated primers that occur with only moderately high pressures. These are things to consider as the gunsmith making and installing a replacement firing pin.

With the dimensions at the front end of the firing pin determined, the main body is cut to length, which is 0.735 inch on the Stevens rifle. The main body is then rounded off to avoid sharp edges where the hammer strikes it. Next the groove is cut along the firing pin body for the firing pin retaining screw. This screw hole is threaded from the top of the receiver immediately above the firing pin hole. I used a 1/8 inch carbide end mill to cut the groove in the firing pin body, which I cut to a depth of 0.100 inch.

The existing firing pin had a milled flat spot fully across the top radius which I felt I could improve upon. My primary reason for making a groove at exact retaining screw diameter was to restrict rearward firing pin travel beyond firing pin nose-breech-face clearance. This, in itself, helps to prevent perforated primer material from entering the firing pin hole as the firing pin is driven to far rearward.

Further, the hardened firing pin retaining screw serves as a positive firing pin stop as the slot radius and screw radius fit perfectly together. This is important in the event of a major primer gas leak preventing the primer from being driven too far rearward. The inner firing pin body radius controls this depth and should be approximately 0.075". A more pointed firing pin may tend to cause primer perforation, particularly where higher breech pressures are generated.

The firing pin has no return spring and travels freely inside the breech. I applied a couple drops of oil to it for free travel and tested it for function. The firing pin functioned without flaw. Primer indentation was perfectly centered and formed a nice sphere at proper depth. Conclusions A seemingly minor job like replacing a firing pin on a single shot firearm must be performed correctly or some unanticipated problem can arise. While replacing such a firing pin, improvements over factory issue can be made. AG