Hard To Pin Down

Accuracy problems? Maybe it’s the firing pin!

If there is a firearm using metallic cartridges that operates without a firing pin, I’m completely unaware of it. In fact, the firing pin is the most important part of any firearm. Without one, a gun is little more than a conglomeration of parts. A firearm’s primary purpose is to slam the firing pin into a primer with enough force to cause ignition.

Some firing pins are relatively tiny. This one on the hammer of a U.S. Firearms
single action is the early cone-shaped type. It is nearly impossible to break.

A Cornucopia Of Pins

Firing pins come in an amazing variety of styles and sizes. Bolt-action rifles, as a rule, have long firing pins about the length of the entire bolt body. Some handguns such as Colt Single Action Army sixguns have very small firing pins. They are so small as to appear fragile but how many have you ever seen broken? It happens but is rare. Firing pins are not always straight in shape. Old Smith & Wesson #3 revolvers had curved firing pins. Old Sharps “buffalo rifles” had a dog-leg-shaped pin arrangement. In revolvers, firing pins over the years have gravitated from hammer mounted to frame mounted. However, it should be noted Colt Conversion .44 revolvers introduced in 1871 had frame-mounted ones.

A tale of three pins: A broken firing pin for a modern Sharps Model 1874 replica
(left), a Remington #1 “Rolling Block” showing a broken firing pin tip (middle) and
an original Model 1874 transfer bar with the firing pin broken off.

Like The Battery Bunny

After what I said in the initial paragraph, the following statement may seem odd — some varieties of firearms will continue shooting with broken firing pins. I’ve seen it happen many times and experienced it myself. The ones I’ve experienced are BPCRs (black powder cartridge rifles), namely a Sharps Model 1874 and Remington #1 “rolling block.” Once I was shooting an original Sharps ’74 at a silhouette match. My score started out great but deteriorated to the embarrassing level by the event’s end. As I carried the rifle back to my cleaning bench muzzle down someone noted, “Mike, something fell out of your barrel.” It was the firing pin.

Those Sharps ’74s were designed so their pins were “captured” in breech blocks. After breaking, they won’t fall out until the rifle’s muzzle is pointed downwards. Even broken a tip can still be pushed by its “transfer bar” with enough force to ignite the primer but it’s not as beneficial as it might sound. Floating loose in its “tunnel,” a broken pin hits the primers with a variety of force. For the best ignition and therefore the most consistent of powder burn, primers must strike consistently. I’ve heard self-styled experts say, “All a primer has to do is go off; then its job is done.” Not so. Light or variable firing pin strikes can cause vertical stringing and/or dismal groups. At BPCR silhouette matches, if a competitor’s rifle with known accuracy suddenly “goes south” the first thing experienced shooters say is, “Check the firing pin.” It is usually the culprit.

Japanese Type 14 8mm Nambu semi-auto pistols had such a reputation for breaking
firing pins they came with a spare and their holsters even had a special slot for them.

If a shooter gets vertical groups such as this one, Duke says to check
for a broken or otherwise impinged firing pin.

But Sometimes It’s Not …

A firing pin doesn’t necessarily have to be broken to cause problems. Anything impinging on its strike to primer will cause erratic accuracy. One of my Shiloh Sharps .45-70 Model 1874’s impressive precision suddenly disappeared. On inspection the firing pin was fine. Deeper searching revealed something in the lock plate had shifted causing the hammer to slightly rub on the edge of the breechblock in falling. Once it was rectified, shooting precision returned. With old military rifles I’ve seen mediocre groups turn to very good ones by cleaning dried oil or Cosmoline from bolt body interiors. The dried “gunk” in there had been cushioning firing pin travel or the firing pin was not able to move far enough forward to ensure positive ignition.

Speaking of military firearms, from my experience the two with the most unusual firing pin set-ups are Japanese Type 14 Nambu 8mm semi-auto pistols and U.S. M1A1 .45 Thompson sub machine guns. The Type 14 Nambu’s had such a reputation for breaking firing pins the Japanese Army and Navy issued them with a spare. Their holsters even had a special slot to store those spare pins — such things couldn’t give a Japanese officer much confidence in their sidearm.

Conversely, the American U.S. M1A1 “Tommy Gun” didn’t have a separate firing pin at all. It was a simple nub machined into the bolt face. Those submachine guns fired from an open bolt, i.e., the bolt is always locked back until the trigger is pulled, so there is no danger of an accidental “slam fire.” I’m not saying it’s impossible for an M1A1 Thompson’s firing pin to break but I cannot see how it would have been possible.

Firing pins are absolutely necessary but can be a source of despair for shooters if not inspected regularly. When a good rifle or handgun starts shooting poorly, the firing pin and/or its ability to strike primers properly is the first thing I check.

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