Shooting an AR-15 underwater

It turns out an FMJ 5.56mm round travels four feet underwater before running out of steam.

How long before someone creates a underbarrel speargun?

[ Many thanks to jdun1911 for emailing me the link. ]

[ Video from MyGunExchange ]

Steve Johnson

Founder and Dictator-In-Chief of TFB. A passionate gun owner, a shooting enthusiast and totally tacti-uncool. Favorite first date location: any gun range. Steve can be contacted here.


  • AJ

    Wouldn’t the water inside the length of the barrel, and the pressure of the bullet, cause the barrel to blow?

    Somethings not right here.

  • wos
  • Bryan S.

    Assault rifle?

  • John Waters

    They should try this using one of those 40gr Barnes Banded Solids.

  • D

    sound is many times more powerful underwater than it is in air. How did they get away with that without going deaf

  • Big Daddy

    I pretty sure that’s a piston rifle. As far as I know a DI one will not shoot underwater.

  • David Black

    I’d heard of the Russian APS that wos mentioned, but hadn’t seen it before. There’s a video up on YouTube now, which also shows the 4 shot pistol they use:

    Pretty cool 🙂 I love the Engineering behind unusual guns, it’s one of the reasons I love this blog!

  • Didn’t somebody have an underbarrel harpoon gun at SHOT or something lately?

  • Lance

    Hmmm he sould try M-855 and see if they go loger out.

  • Burst

    It seems like it’d be pretty easy to make a underwater shotgun shell.
    Waterproof the primer until it’s hit, then use a compressed air cell to launch some flechettes.

    Worst part would be getting water in the action, but you could allow for that with a purpose-built shotgun.

  • Big Daddy,

    I’ve seen it done with a standard gas tube. It sometimes work, and it sometimes blows the gas tube out.

  • jdun1911

    Piston rifles can not defied the law of physic.

    It doesn’t matter if it piston or DI. You’re not suppose to fire a rifle underwater because you know the water clog up the barrel. Objects that clog up the barrel is bad. Right?

    I would like to know how he did this experiment and what ammo did he used.

  • David, thats is an awesome video. I just blogged it.

  • Vaarok

    There’s a speargun conversion for 10/22s that uses power-nailer blanks. And the crossbow upper for ARs.

  • Michael

    I’ve heard stories about this before but the physics part of me says you can’t fire a gun under water. Water doesn’t compress, at all. That having been established I would feel confident the barrel would rupture and the projectile would competely fragment without some type of modifictaion to the barrel that will allow the water to freely get out of the way. But even then, I can’t imagine a barrel surviving. I guess if you ported the barrel from the chamber forward it might not rupture, but even if it doesn’t what has been accomplished?

  • Alex

    I’m surprised it even cycled

  • Michael Barncastle, Sr.

    I would imagine if you put a very thin ballon type of insert into the barrel it would prevent the barrel from flooding with water. That should allow the projectile to make the trip down the barrel until impacting the water at the muzzle? Of course, the [projectile still isn’t going to be very effective after exiting the muzzle for more than a couplke of feet or so.
    When seconds count, the police are only a few minutes away!


    That’s what I was thinking of… don’t know how much better it would work underwater though.

  • Michael Barncastle, Sr.

    I think all that would accomplish is preventing the barrel from being ruptured? Other than that the projectile would probably still just go to pieces after leaving the air pocket, and, or, abruptly stop.