Firing Pin Gauge

In American Gunsmith January 2021, RK Campbell’s article "Firing Pin Logic and Mechanics" discussed firing pin protrusion as being a potential cause of misfires and light primer strikes. If the firing pin does not strike the primer deep enough to crush the priming compound against the anvil and cause ignition, a misfire occurs. If the firing pin protrudes too far it can pierce the primer and cause blowback or other problems.

SAAMI defines firing pin protrusion as, "The distance the firing-pin protrudes from the breech face when it is in its most forward position." Brownells provides some general rules for firing pin protrusion. Centerfire rifles and handguns usually measure between 0.050-0.060", shotguns between 0.055-0.065", and rimfire guns between 0.028-0.035". These may vary depending on the make and model of the firearm.

The type of firing pin, such as inertia firing pins as found in the 1911 and similar models, slanted pins in overand-under shotguns, and other Notice the center of the aluminum tube is drilled and tapped for the 8-32 set screw. designs can also see variations in these dimensions. These other designs may provide exceptions to these rules and be more difficult to measure. I recently purchased a used Ruger Redhawk double action revolver that has a transfer bar.

This particular model has a history of light primer strikes caused by a short firing pin or misaligned transfer bar. I wanted to measure the firing pin protrusion to ensure I would not have this problem. Required Materials To make the firing pin protrusion gauge I used a one-inch piece of 1/4-inch diameter aluminum tube. The inside diameter of this tube was 1/8-inch. I used the shank of a broken 1/8-inch milling bit ground to the same length as the aluminum tube.

A broken drill bit, 1/8-inch welding rod, or any other 1/8-inch rod stock will work. I used along 8-32 set screw as a lock for the gauge. If you have a manual caliper, write down this measurement. I drilled the center of the aluminum tube with a #29 drill bit, tapped the hole with an 8-32 tap, and installed the set screw. I inserted the 1/8-rod in the tube and locked it in place with the set screw and then ground both ends of the assembled gauge flat and square so the inside rod was flush at both ends.

This is important to get an accurate reading. Measuring Pin Protrusion Safety first; ensure the firearm is unloaded. This procedure requires the cylinder of a revolver be removed or open, or the rifle bolt removed. When measuring firing pin protrusion, it is important to note that the firing pin must be in its normally extended or fired position and there needs to be enough space to use the gauge.

For my Ruger Redhawk that meant I had to have the cylinder open and be able to pull the trigger so the hammer was against the transfer bar and the firing pin was extended beyond the breech face. For a rifle, the bolt