AR-15: Over the Beach Test

[Picard]

I was wondering if you guys with more AR experience than I could help me out with this.

I'm sure many of you have seen this video of the HK 416 vs. Colt AR-15:
http://www.youtube.com/watch?v=AGwkHktkTxU

At about 1:25, the Colt blows up after being submerged in water.

I figure, ok, it blew up because there was water in the gas tube, causing over-pressurization and a catastrophic malfunction.

Now watch this video: http://www.youtube.com/watch?v=unYAcHIUhXE

It passes the test perfectly, also being a DI AR-15.

Now, is it because the guy in the second video waiting an extra second before firing? Is it because he cycled the action before firing? I'd like to hear your guys' input.

[ClickClickD'oh]

Oh god, not the HK416 garbage again.

It blew up because HK wanted it to blow up. Notice the surprisingly obvious change in protective equipment between the HK and AR.

[Combat Diver]

Because the barrel was blocked on the Colt (bore obstruction). I've seen guns fire submerged before, its when you have air and water in the barrel that you have an obstruction. HK would have done the same if obstructed.

CD

[Picard]

If it was a bore obstruction, how come the XCR can handle it?
http://www.youtube.com/watch?v=Db8mmURVswc

Are you sure it's not something to do with the DI system on the AR?

[theotherwaldo]

I still liked the final screen of that video:

"LEADING TROUGH TECHNOLOGY"

[RecoilRob]

Yep, H&K are the top of the heap.

[Picard]

"LEADING TROUGH TECHNOLOGY"

So what if they specialize in feeding farm animals. They're good at what they do.

Does anyone have an answer as to why the XCR didn't kaboom in that video? I would assume that it would also have had water in the barrel.

I'd like to know the capabilities of the AR platform without risking blowing my limbs off.

[Combat Diver]

Vids are blocked at my end. Did it show the DI guns getting the barrels cleared/drained compared to the others?
M4s work when coming out of the water but you have to clear the guns first. Any gun not cleared will kaboom. Used to do it for a living for 15 yrs.



CD

[swgunner]

Combat Diver is spot on. Always open the action to break vacuum. Sailors are a tad bit more familiar with this because of our operational environment, but water in gun barrels is not an optimal condition.

[Picard]

@Combat Diver
So what do you recommend if an AR gets dunked and you need to shoot it ASAP? Cycling the action?

[James T Thomas]

I will concede to Combat Diver's experience on this one.
But may I tell you from my experience: only being submerged chest high and having the occasional dunking from stepping into a hole now and then.

The 30 caliber bore drains much more readily than the 22 tube.
My suppostion is that the blockage was a column of water being forced along the barrel ahead of the bullet caused the destruction of the gun.
The additional water was equivalent to firing so much more than a 55 grain projectile.
While the gas tube may burst, most likely, that would result in loss of automatic function.

When you have spare seconds; withdraw the bolt and incline the bore vertical.
Examine your ammunition round by round for water borne debris.
And clean out your magazines too.

[Freiheit]

If its not safe to fire the weapon when you come out of the water without cycling the action or clearing the bore, what do you do when you pop out of the water and have to shoot a bad guy? Just squeeze the trigger and pray?

Would something like condoms over the flashhider help for water? I recall hearing about troops in Desert Storm doing that.

[RecoilRob]

I think the condoms were more for the sand infiltration than moisture. If the gas tube has water in it, it is going to open the action prematurely....which is bad. The water in the barrel goes up the gas tube at the shot and doesn't wait for the bullet to get past the port....so it opens early and goes BOOM!

If you watch the video closely with a stop-watch, I got the HK shooting around 1.9 seconds after clearing the water, while the poor M4 was fired in just under a second. They WANTED the M4 to blow up, and waiting that extra second would have made it more unlikely.

Racking a round through the action should let enough water out of the tube that it won't kaboom on you. So, for frogman duty, the HK might be better. But....I can't remember the last time I had to jump out of the water and shoot somebody. Happy about that too!

[KodiakBeer]

I suspect there's an incremental reliability advantage of a piston system over a DI system, but crawling out of a pond and shooting is not one of those advantages.

Maybe Colt should blow up a couple of H&K's on Youtube?

[Picard]

The water in the barrel goes up the gas tube at the shot and doesn't wait for the bullet to get past the port....so it opens early and goes BOOM!

That makes perfect sense. How about a rifle like the AK or the XCR, which is based off of the AK? It doesn't seem that water in the barrel would make one Kaboom, as seen in the video previously posted: http://www.youtube.com/watch?v=Db8mmURVswc

I think the answer to my original question lies in the gas tube and I think that RecoilRob nailed it.

[Combat Diver]

Ricard,

Others have mentioned it. With a 5.56mm weapon with its smaller diameter you must break the seal around the bolt to drain the weapon. I swim with a muzzle cap on and remove it just prior to surfacing (to keep silt/mud out of the bore, not water). Larger bores as mentioned do not have the vacum effect that the smaller bore does.

If I had to shoot immediately coming out of the water I was already dead as this is a no win situation for me. As I'm exposed and can not move rapidly. My job was to sneak in undetected, if I didn't then I failed in my insertion mission.

CD

[MechAg94]

Since we are talking about theoretical situations of coming out of the water shooting; just leave the bolt open and release it as soon as you come out of the water.

Other than that, I agree with Combat Diver.

I believe HK also makes or used to make an underwater pistol.

[RecoilRob]

What would be REALLY interesting would be to take an AR-10 and try the 'shooting within two seconds of surfacing' to see if it is the bore diameter or the DI gas operation at work in the blow-up.

I do think the primary mechanism at work here is the gas tube being full of water. The bullet pushing the barrel full forward....even if it doesn't over-pressure from just that alone, applies equal hydraulic pressure to the water in the gas tube as that coming out of the muzzle.

Being in direct contact with the carrier, this shoves it rearward without the benefit of proper timing. I've been wondering about the piston mechanism and how it seemingly tolerates this abuse. The hydraulic phenomenon should happen to it also, but perhaps the piston doesn't move as easily as far being larger diameter which gives the carrier just a fraction more time to avoid destruction. Doesn't the piston type action get a 'running start' at the carrier too? If so, that additional movement before starting the unlocking might make the difference in this test.

Something tells me that the HK does NOT do this test all day without damage as they imply. One Colt disassembled and one HK didn't after a few tries, but this isn't saying that it wasn't just on the verge. I'd like to see the cases from those first shots....bet they are bulged and nasty looking.

[swgunner]

One the principles of hydraulics is that when you have the same pressure but decrease surface area you get a higher pressure.

In the AR 15 or any DI system you are going to get more volume (water from the barrel going into the gas tube that already has water in it) and a smaller surface area, in effect you just quadrupled your hydraulic force. That kind of pressure increase cannot be good for anything.

On a side note if we do a helo-cast or swim mission, our primary weapons are sealed in special ziploc bags. AS combat diver mentioned if you get caught infiltrating you already failed. Most of the time however we used small boats and radioed our intention to board. Sometimes we got to be sneaky.