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Is AR-15 drop safe?

Discussion in 'Rifle Discussion' started by mattg521, Mar 21, 2013.

  1. mattg521

    mattg521 portland.,or Member

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    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?
     
  2. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    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.
     
  3. del_and_bones

    del_and_bones Anchorage, AK Physics Pirate

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    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...
     
  4. ocarolan

    ocarolan Portland, Oregon Well-Known Member

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    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:

    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.
     
  5. mattg521

    mattg521 portland.,or Member

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    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.
     
  6. dracozny

    dracozny Oregon Member

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    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.
     
  7. shooter58

    shooter58 Vancouver, WA Active Member

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    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…
     
    Nwcid and (deleted member) like this.
  8. Capn Jack

    Capn Jack Wet-Stern Washington Bronze Supporter Bronze Supporter

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    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. :paranoid:

    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...:cool:
     
  9. Medic!

    Medic! What just happened? Has eagle eyes. But cant remember what he saw. Bronze Supporter

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    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.
     
  10. mattg521

    mattg521 portland.,or Member

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    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.
     
  11. Nwcid

    Nwcid Yakima and N of Spokane Well-Known Member

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    iamme and (deleted member) like this.
  12. Medic!

    Medic! What just happened? Has eagle eyes. But cant remember what he saw. Bronze Supporter

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    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!
     
  13. speeddemon94

    speeddemon94 The Rogue Well-Known Member

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    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.
     
  14. Netspirit

    Netspirit Bellevue, WA Active Member

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    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.
     
  15. Ben Beckerich

    Ben Beckerich NW Oregon Bronze Supporter Bronze Supporter

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    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.
     
  16. Ben Beckerich

    Ben Beckerich NW Oregon Bronze Supporter Bronze Supporter

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    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.
     
  17. Ops

    Ops King County Member

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    keep your finger off the trigger and it wont go boom
     
  18. del_and_bones

    del_and_bones Anchorage, AK Physics Pirate

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    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.
     
  19. rick benjamin

    rick benjamin USA, Or, Damascus Secure the drama Silver Supporter 2016 Volunteer

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    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...
     
  20. Trailboss

    Trailboss Vancouver, WA Well-Known Member

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