AK-47 Underwater VS AK-47 Out Of Water – Dat Piston Speed

High speed camera shows drag:

I wonder if that’s his kid’s fish tank?  I remember I had fish a few times… what a shitty pet.  I still would like to get rays and sharks someday in a massive baller-status wall tank.  I’d have people look after it though.

That looks pretty sweet when the glass spiderwebs and explodes.

AK-47-Kool-AidWATER = FASTER?! omg my entire world just came crashing down on me.  Damn you science *shakes fist into air and drops to knees*.  It does make perfect sense when he explained it thankfully.

Thoughts?  Oh and if you have a baller-status shark / ray tank please email me pics.

Hat tip: Joethefatman, Kevin, Carl



Ronald RayGun June 26, 2013 at 01:11 am

No lie, that’s a sick ass AK. Dat FDE!


santi June 26, 2013 at 06:47 am

That was a great video. Cool guy too.


SittingDown June 26, 2013 at 10:20 am
M June 26, 2013 at 03:02 pm

Pretty cool!

I’m not sure that i like his explanation of why. The water in front of the bullet won’t actuate the piston because it has an easier path to follow out, the muzzle.

The fact that water cannot be compressed might have something to do with it, therefore it transfers the motion faster than air. Just like having air in your brake lines makes the pedal spongy, air in the brake lines doesn’t transfer the motion as well because it compresses.

Two other things might be playing a part:
A: Because of the resistance that the bullet is encountering (pushing the water out of the bore) it is traveling slower as it passes the gas port, giving the gasses more time to push on the piston before the bullet exits the muzzle, and increasing the overall pressure of the gasses in the barrel.

B: as the hot gunpowder gasses travel down the barrel they are vaporizing any water left in the barrel, creating steam. As the steam is generated it expands, occupying more space and increasing overall pressure. It’s debatable how much water would be left in the bore after the bullet is pushed out, acting like a squeegee. But when the hot gasses hit the gas port there is all of that water to vaporize too…

I’m kind of surprised how dramatic the difference was though! I’ll bet that if there were a way to only submerge the barrel and gas tube, leaving the bolt in the air, that the effect would be much more dramatic because you wouldn’t have the increased drag on the bolt.

One more thought… This guy wouldn’t go through so many fish tanks if he tilted the guns muzzle up, so that the bullet could clear the glass! Of course he’d have to rely on something other than a pile of dirt to stop the bullet… or dig a pit…


Smooth Operator June 26, 2013 at 03:56 pm

This makes perfect sense when explained, although I was at first surprised with the results.

My question: would the cycle rate of a blowback gun (like keltec sub 2000 or similar) become slower underwater because there is no gas system? In that circumstance the primary factor should be resistance against the action as opposed to speed of force transferred through to op rod/piston.



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