Is AR-15 drop safe?

[mattg521]

BCG on the AR-15 appears to have a free floating firing pin. This suggests to me that a hard drop could cause ad/nd. Is there some design aspect I'm missing that makes it "drop" or inertially safe?

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[Nwcid]

Yes physics make it safe.

With the light weight of that pin it would take a crazy amount of force/inertia to be able to set it off.

 

[del_and_bones]

Hmmmm... I'm going to test the amount of force applied by an AR15 firing pin over spring break and then give you guys a drop height. Stay tuned...

 

[ocarolan]

I dropped mine once as an experiment with a new snapcap (about 3 ft) and it did not even dimple the round. So the force of closing the bolt on the firing pin (which dimples the chambered round), is probably more than many drops.

There are anecdotes of drops causing discharges, but some people attribute this to an inadvertent bolt closure, not the drop itself.

Eg, THR thread:

I have seen M-16A1 rifles fire on bolt closing. The position of the safety had no bearing on the event. Call it a sensitive primer, but the round being chambered fires. I have seen this with loading the weapon on a range and have seen mechanically sound guns "double" when the round after a single shot goes off un intentionally.

In my Infantry Company in 1974 a gate gaurd was severly injured when a rifle with a loaded magazine in the weapon was dropped from a height of about 3 feet. The M-16A1 rifle had one of the older "rubber" butt plates with out the trap and the butt struck first with the barrel pointed straight up. The bolt ran back far enough to chamber a round. We confirmed this later by recreating the event and when dropped from the height of the same window ledge butt first both the rifles with the rubber butt and the hard trapdoor butt generally did feed from the magazine, though as we used a dummy round there was no chance of the rifle firing.

The trooper bent over to catch the falling rifle and was struck by a round of M193 ammo. He did manage to stay on duty about fifteen minutes including opening an closing his gate until someone noted the blood and opened his M1967 body armor he then rapidly lost the ability to stand and remain on duty.

Oddly I have not seen a fire on loading inciedent in civilian life, but have seen the occassional double I could find no other explanation for.

It puts me in mind of the importance of the old NRA GOlden RUle of GUn Safety "Always point the muzzle in a safe direction"

I have seen the resuts of a round of M193 ball striking a concrete floor at zero angle or ninty degrees how ever you choose to say it. It left a small crater about one inch across and not that deep and the bullet was reduced to small as in sand sized fragments......unfortunately the bullet passed through a GI boot and the GI foot in it on the way. Moron holding the muzzle straight down on his boot and holding the butt at waist level. The rifle had supposedly been twice cleared including on rodding ("No brass or ammo Drill Sar'nt!") and was about to be turned in. SOP in the unit was to leave hammer down on an empty chamber and hamer down so the safety on the M-16A1 would not engage. His was on safe. When this was pointed out he flipped the selector to fire and pulled the trigger. He was talking to me at the time and after the shot I recovered the rifle and made it clear, then rendered aid. Point is though that the bullet did not do well AFTER striking the concrete... did fine before.

A drop might cause a very light trigger to discharge, of course.

Not directly related, but I remember Clint Smith said some police depts require officers to transport their AR15s unloaded, because a patrol car crash might cause a discharge. You'd think there would be stories of that actually happening in the military though, if it were possible.

 

[mattg521]

Hmmmm... I'm going to test the amount of force applied by an AR15 firing pin over spring break and then give you guys a drop height. Stay tuned...

Wow that would be so scientific and awesome. Mythbusters style. Will you resort to explosives if necessary? In all seriousness thanks and looking forward to your post.

 

[dracozny]

properly maintained there should be no issue at all. defective weapon you might see a slam fire failure. still have not found any evidence of a drop test failure.

 

[shooter58]

In my experience if an AR is dropped on its butt then the bolt carrier would try to move as if being cycled so not much chance of discharge unless as mentioned, the hammer moved off the sear. No idea what might happen if dropped on the muzzle...

 

[Capn Jack]

In the early days of reloading for my AR15 (.458S), before I had my reloading dies
adjusted properly for my rifle, a loaded cartridge would often stick 98% into the
chamber and have to be "Mortered" out.

This is done by striking the buttplate on the shooting bench while forcing back on
the operating handle. Sometimes several bangs against the bench would be required
before the cartridge was ejected. This was accepted procedure and done by many
before chamber test dies became common usage. All without any record of an accidental
discharge.

Jack...

 

[Medic!]

The fireing pin has no spring and is free floating like the 30 carbine,garand and m-14. If you load a round in the chamber with the full force of the buffer spring you will see a dent in the primer. When the bolt stops in the forward most position, the free floating fire pin slams into the primer. It dose not have enough mass to fire a hardeded rifle primer. But use a softer primer and all bets are off! Dont believe me? Load a round then eject it and look at the primer. Kinda scary?
There is no spring. So no spring energy holding the firepin off the primer when loaded. Gravity will cause the pin to touch the primer or not. Just buy pointing the barrel up or down. So a drop on concrete or rock on the rifles muzzle, could fire a round if it emparts enough energy to the fire pin just resting on the primer.

 

[mattg521]

The fireing pin has no spring and is free floating like the 30 carbine,garand and m-14. If you load a round in the chamber with the full force of the
buffer spring you will see a dent in the primer. When the bolt stops in the forward most position, the free floating fire pin slams into
the primer. It dose not have enough mass to fire a hardeded rifle primer. But use a softer primer and all bets are off! Dont believe me? Load a round then eject it and look at the primer. Kinda scary?
There is no spring. So no spring energy holding the firepin off the primer when loaded. Gravity will cause the pin to touch the primer or not. Just buy pointing the barrel up or down. So a drop on concrete or rock on the rifles muzzle, could fire a round if it emparts enough energy to the fire pin just resting on the primer.

That is exactly what I was thinking when I started this thread. Cid says the pin is too light to actually cause ND. Perhaps Del will provide the scientific answer.

 

[Nwcid]

Here are tons of threads all over the net on it, ar 15 drop safe - Google Search

 

[Medic!]

I know that when I sliped and fell off a wet mossy log when hunting, that my rifle did not hit the ground. I fell about 10' to the dry creek bed and landed on my side and back with my rifle held up over me in my right hand. We were tought in the Army not to let the weapon hit the ground. If that gun is damaged you are as good as dead on a battle field. So don't drop your gun!
If a rifle or pistol dose get away from you, don't try to grab it. Let it fall! Grabing at a falling gun is a fantastic way to shoot yourself or someone. Modern guns are not likely to fire a round anyways when they are droped and hit the ground. Even when cocked. It's a hard erge to resist. Especialy when you have miliseconds to think over your beautiful gun geting scratched or even badly damaged. So think on it befor it happens.
Then you may not be as likely to grab at it. That scratch in your Python will learn you a lesson! Handle a gun with purpose. Don't be dainty with it. Don't drop your gun!

 

[speeddemon94]

I had one go off with a blank in the chamber once. It can happen. That was an M-16 A1 Army issue. It was a fairly worn out rifle. After it did it that time, we attempted to duplicate by slamming the butt of the rifle and the buffer was weak enough we could get it to eject the chambered round.

We finally figured that the repeated chambering of one round, dimpled it and just finally hit it hard enough to set it off. Luckily it was a blank. Made me very careful about rotating rounds.

I always thought a light spring could be somehow incorporated to keep that firing pin from dimpling the primers. Maybe I'll work something out on the 300blk I'm planning.

 

[Netspirit]

I have not seen any stats on AR-15s going off when dropped. In fact, multiple articles on the web are saying that police officers, used to shotguns not being drop-safe, are treating AR-15 rifles the same way which is unnecessary.

I have no idea who is right but I try to treat all weapons as drop-unsafe, just like I consider them loaded until proven otherwise.

 

[The B]

No- ARs are not "drop safe."

Neither the FCG or firing-pin disengage- when the weapon is charged, it's nothing more than a component-failure away from discharging.

 

[The B]

In order for something to be "drop-safe," it needs to be engineered in such a way that the firing pin and generally also FCG components are physically disengaged when the trigger is not depressed. Having a piece of fail-able steel blocking the hammer from swinging into the firing pin definitely does not qualify. The Glock "safe-action" system does, because the striker doesn't even line up with the primer until the trigger is depressed- any part of the gun can fail or break, and the weapon will still not fire.

 

[Ops]

keep your finger off the trigger and it wont go boom

 

[del_and_bones]

Update: I just tested my firing pin with a force sensor and some data acquisition software. I'll give two answers: the short answer only gives the drop height, the long answer will walk through my method and calculation.

Short answer:

I calculated that an AR15 dropped from 0.30 feet on its muzzle *should* discharge if a round is in the chamber. This does not seem to be correct, I think the sensor I'm using is not fast enough to accurately register the force.

Long answer:

The force sensor is a small black box (2"x2"x3"and ~1oz) with a rubber stopper (probe end) on the end which protrudes from the long end. It uses piezo-resistors to change the resistance when they are compressed or stretched and thus the data acquisition software can deduce the amount of force at a given time.

For the experiment I stripped my AR, set the force sensor on the magwell of the lower with the probe end about 1/8" to 1/4" hanging into the FCG area, took off the safety and pulled the trigger. This sent the force sensor flying. From here the computer plotted the force versus time, from which I gleaned my results.

By integrating the force over the time of the collision, I was able to calculate the impulse (J) imparted on the sensor. Since

J= delta P = integral(F dt) from t = initial contact to final contact

I found the average impulse for 7 trials to be around 0.16 N*s (aka kg*m/s). Using the mass of a firing pin (found here), I found the final velocity of the firing pin (J/m = v). I then used conservation of energy, the concept that the initial potential energy is equal to the kinetic energy when the rifle hits the ground mgh=1/2*mv^2, to solve for the velocity v=sqrt(2gh). Now I set the equations equal and arrive at the result when I solve for h.

h = 1/(2g)*(J/m)^2
for our use:
J=.16
m=.120
g=9.8

Which gives 0.09 meters = 0.30 feet = 3 9/16 inch. This does not seem to be correct, I think the sensor I'm using is not fast enough to accurately register the force.

Conclusion: don't drop your rifle.

 

[rick benjamin]

I know for a fact that bad things happen when an M16 is dropped.
The drill instructor taught me to never drop it ever again...

 

[Trailboss]

We need a volunteer to drop their AR from a ten story window onto concrete. Sorry, my AR is busy at that time.