Inertial Discharge of the M1911 Pistol
By John De Armond

Others said:

#>> Ever dropped a 1911A1 on the muzzle? #>
#> Good point, bad example. M1911A1 is one of the safest pistols wrt accidental
#> discharge, with three distinct safety mechanisms.

#None of which does the least bit of good when you drop one muzzle first.
#The floating firing pin can slam forward with enough force to fire the
#gun when dropped on concrete, or other hard surface, muzzle first. The
#new Series 80 with the firing pin block brings the 1911 style into the
#late twentieth century by preventing this problem. Most other modern
#pistols don't suffer from this defect.

I've heard this bad rap against the 1911A1 (henceforth referred to as Colt) many times both in this group and in the magazines. That dropping a Colt on its muzzle being capable of igniting a primer goes contrary to my intuition. I finally decided to test this theory. I have done two tests. The first tries to scale the problem. The second involves actually dropping a gun.

Test #1 is to determine how much force is required to compress the firing pin spring sufficiently for the business end to protrude from the bolt face. Once this value is determined, the firing pin can be weighed and the number of Gs required to exert this force can be computed.

The test firearm is a box-stock Series 70 Colt Gold Cup. It was freshly cleaned and all oil film that could be wiped off was. The test setup is simple. I clamped the slide in a vice with the rear pointing up. A small drift was placed against the firing pin and Orhaus lab weights were stacked on the firing pin until the spring was compressed sufficiently that the firing pin barely protruded from the bolt face. Then the drift was weighed on an Orhaus triple beam balance and the weight was added to the lab weights weight. Finally the firing pin was weighed on the same balance. Results:

            Firing pin weight:                         4.4 grams

            Total weight required:                  506 grams

            Computed G force:                       506/4.4 = 115 G

Note that this is the minimum force needed to make the firing pin barely protrude. This does not account for the force required to actually fire the primer. I tried to get a rough idea of what this force is by putting a primer that had been inserted in a case, placed the casing in a barrel and slide assembly minus the firing pin spring and then placed weight on the firing pin sufficient to cause the first dent in the primer. The primer was a Winchester large magnum pistol primer. I ran out of weights at 4 kg. No dent. That would be equivalent to about 1000 G of force. If anyone has factory specs on the required primer force, I'd love to have them.

Keep in mind, that these static tests do NOT account for the pretty significant aerodynamic counterforce involved with a firing pin propelled at sufficient velocity to fire the primer. Once the firing pin protrudes into the bolt hole, the pin and bolt forms a fairly tight cylinder with air trapped inside. This damps the pin and absorbs some portion of the force.

Based on these results, I got brave and proceeded on to the next test. An old slide, bushing, barrel and the Gold Cup firing pin and spring were assembled. A case with a live primer was chambered and the whole assembly was duct taped to make sure the barrel stayed in battery. Then the whole assembly was dropped muzzle first down various lengths of pipe onto my asphalt driveway. The pipe guided the assembly and made sure the muzzle remained pointed straight down.

The longest pipe I could find was 15 feet long. Several drops from this altitude failed to fire the primer. The primer was marked but not enough to call it a dent. I did one more drop with the firing pin spring removed. The primer was dented pretty severely but it did NOT detonate. I suspect that with several drops, one or more might fire the primer. I got bored and my slide was getting boogered up so I stopped with the one drop.

 Based on these tests, I feel confident in saying that there just ain't no way dropping a Colt on its muzzle is going to inertially discharge the thing. I could believe that dropping a tinkered-with or hot-rodded gun could cause the sear to break, dropping the hammer and firing the gun. I would believe that people who cause ADs would claim that dropping the gun caused it 'cuz they were embarrassed. But I would have major doubts that dropping a gun even with the firing pin spring removed would do anything.

 Methinks the Colt has gotten a very bad rap and that the firing pin blocking gimmick placed on Series 80 and subsequent Colts is just that - a lawyer gimmick. Looks to me like the original Colt designers did their homework.

 -- John De Armond,