Mister Science hits the range....

[fish2xs]

Couple weeks ago I was at the range and firing .308 surplus ball ammo at two plastic
bottles, both filled with water and sealed tight. Targets were 150 yards away. One bottle
was 2 liter the other was smaller (don't recall the exact size, but it was a bit smaller than
a 12oz beer bottle).

Both targets when hit the first time, fell on their sides. Other than falling, there was no
perceivable change I could see. The second shot that hit them caused each bottle
to explode massively.

....Why? I would expect the first shot to have caused the explosion. With openings in
the bottle and less water, I assumed pressure would have escaped without blasting
the bottles into smitherines.

Other factors:
outside temp was about 30 degrees F
bottles were filled almost to capacity - no ice
bottles were placed on the side of a dirt backstop
I don't know how much water leaked out before the second hit

...note I'm assuming that both bottles were only hit once prior to the devastating impact,
and that the first couple shots probably missed. Post contact autopsy of the remaining
2L plastic fragments indicated only one other hit, but it was starting to snow/rain/blow so I
didn't bother with re-assembly. the smaller bottle was just plain gone....

 

[Owen]

you shot under them, and knocked them over, or you shot high into the air space and knocked them over.

owen

 

[hillbilly]

I agree that you probably hit the dirt beneath the bottles on the first shot and then connected on the second shot.

But here is a related happening I have observed over the years.

When shooting plastic bottles full of water, I have found that I get more spectacular splashes if I fill the bottles only 3/4 full, instead of full. Of course, the bottles must have tight caps for this to work. And I have to hit the water column, usually fairly low on the bottle.

But it seems that when I fill the bottles 3/4 full, the following happens.

Water is not very compressible, but air is. So when the high velocity bullet strikes the water, it is the air in the bottle that gets compressed, not the water.

In essence, the water leaps up into the air space in the top of the bottle, forced there by the passage of the bullet.

And the result is that the bottle flies up in air and water sprays around in a very spectacular, impressive fashion.

Full water jugs I shoot with my AR-15 just kind of tip over and gush water out of the exit hole in one big splat.

Water jugs filled to the 3/4 line jump about 6 to 10 feet in the air, rupture violently, and spray water all over the place. At least when I aim just a little low on the bottle and hit the water column at about its midway point.

It's really cool when you add food color to the water and make impressionistic gun paintings.

hillbilly

 

[fish2xs]

>> you shot under them, and knocked them over, or you shot high into the air
>> space and knocked them over.

maybe on the small bottle, but I don't think this happened on the 2L one. again,
based on the mini-autopsy, I'm pretty certain the 2L bottle had a hit below the
waterline prior to the explosive hit.


but what the hell... I could be wrong.

 

[Dr.Rob]

Which really doesn't compare to lighting up an out of date slightly filled propane tank with a 172gr armor piercer from a full auto BAR.



While the water jug bombs look impressive they don't teach you much.. I like using them to teach beginners how to shoot at unknown ranges.

IE dial in your deer rifle at 100 or 200 yards. Ok come back next week.. see that hill over yonder.. there are five colored milk jugs.. you have five shots.. try to hit them all.

It's tougher than it sounds. Lots of fun too (provided youhave a 200+yard range with a positive backstop, like a large hill)

Oh and Mr. Science... when you light up a gopher with a tracer.. it still smells bad from 100 yards away.

 

[Dave R]

I'm surprised the 2nd shots made the bottles explode.

I did something similar with 1 gal plastic milk jugs. Wanted to test the difference between hunting bullets (expanding) and FMJ in .308.

Lined up 2 rows of 5 each 1 gal plastic milk jugs. Shot 1 row with surplus FMJ. Shot other row with 150gr. Remington Core-Lokt. The row with FMJ--I thought I missed. No visible reaction until I noticed a .30 hole in each jug leaking slowly. The row with the Core-Lokt exploded.

So I'm not surprised the bottles fell over first shot. I think you hit them, and the bullet just zipped through without transferring much energy. Maybe they exploded the 2nd time because you caught the rim, or bottom, which fragmented and transferred more energy?

 

[hillbilly]

On the other hand, maybe this is what happened?

You hit both bottles on the first shot and just punched .30 caliber holes in them.

Then, on the second shot, enough water had leaked out of the holes that there was an air space for the water to be forced up into violently, causing the splatter effect?

hillbilly

 

[hksw]

IMO, what could have happened was that after the first shots, the integrity of the bottle was compromised (weakened) but the holes punched through them. When the second shots went through, the weakened stress points formed by the first shot allowed the bottles to let go easier and caused a more dramatic effect.