PDA

View Full Version : Bulletproofiness of sandbags



Bill
09-27-2007, 01:13 PM
I was watching The Longest Day the other night and it got met wondering, what's the actual bulletproofiness of a pile of sandbags? Like, what sorts of bullets (and at what ranges) can they stop? I've seen videos of bricks and cinderblocks being blasted apart but never real bullets fire at a sandbags.

Drastic
09-27-2007, 01:40 PM
No videos, but the Box o' Truth (http://theboxotruth.com/docs/bot7.htm) site did a--sorta--sandbag shooting bit. Upshot of their anecdotes: 6 inches of sand is a really good bullet barrier.

Sarkus
09-27-2007, 01:45 PM
Not directly the same but similar is Mythbuster's look at how water slows down bullets. The bigger the bullet, the more it seemed to be affected.

Yes, sand is different, but there are some similarities.

Matt Bowyer
09-27-2007, 01:53 PM
The Mythbusters results were remarkable -- I didn't expect that at all.

I would think the sand would deflect the bullet somewhat as well -- in the Mythbusters test of shooting through a sniper's scope, the lenses in the scope were deflecting the bullet enough to keep it from going all the way through.

I also know nothing about firearms, so I wouldn't be surprised to find out I'm dead wrong.

Adam Altmann
09-27-2007, 01:59 PM
I'm not sure where I attained this "knowledge", so don't pay too much attention to it, but...

I believe I saw/read somewhere that, say, a hanging sandbag will easily stop a bullet, but an arrow will pierce or go right through it. Keep in mind that I'm probably full of shit.

Shadarr
09-27-2007, 02:07 PM
I'd be very surprised if an arrow could go through a sandbag. I shot arrows on a beach once, and they didn't even stick far enough into the sand to stay standing. Maybe you're thinking of kevlar?

Talisker
09-27-2007, 02:10 PM
No videos, but the Box o' Truth (http://theboxotruth.com/docs/bot7.htm) site did a--sorta--sandbag shooting bit. Upshot of their anecdotes: 6 inches of sand is a really good bullet barrier.
That's an awesome site!

Pishtaco
09-27-2007, 02:41 PM
In my book on the first world war, which I have unfortunately lent to someone, it had tables from an infantry manual saying how much of different things you needed to stop a rifle bullet. 6 inches sounds short for sandbags; I have a feeling it was of the order of several feet. I'm guessing that part of it is that surely you fill sandbags with dirt, not tightly-contained sand.

Aeon221
09-27-2007, 02:59 PM
According to the Soldier's Manual of Common Tasks (STP 21-1SMCT Oct 1990), you need to ensure that there is at least 18 inches of dirt between you and the enemy in a prepared position.

While it doesn't go into the physics, I'd assume that prepared position means that 18 inches of dirt is enough to slow/stop a bullet. Interesting the shit you find in your parents old gear.

Rimbo
09-27-2007, 03:15 PM
The boxes in the "Box o'Truth" site also had drywall on either side. The drywall certainly had an effect on the bullets as well.

Also, sand is going to have a different effect than dirt, since sand is mainly crushed shells (coarser and more likely to cut into the slug), while topsoil is mostly decayed vegetable matter.

Phil_Stein
09-27-2007, 03:23 PM
Also, in an ideal case, military sandbags would be prepared in such a way as to stop .50 cal and maybe even 37mm shots.

I'd guess that having more mass in a projectile and having the projectile be relatively long (relative to its diameter) would greatly increase the penetrating power of said projectile.

Finally, if we say that 6 inches of sand is just enough to stop small bullets and perhaps 12-14 inches of topsoil is enough to stop most military bullets, I'd still want the extra protection of 18 inches, to give me a margin of protection against a bag that isn't quite filled or stacked right or against other possible issues.

Houngan
09-27-2007, 05:18 PM
Hey folks, friendly neighborhood shooter here. The interesting thing about sand is that it behaves very much like water when shot. If you ever want to see a nice example of bullet expansion, shooting into a sandpile will produce a classic mushroom shape every time. With hollowpoint jacketed rounds, of course.

As mentioned, weight x velocity is important, and caliber is doubly so. Testing against wet magazines (this was before ballistics gel was cool) I found that a .22 magnum is one of the most penetrative pistol rounds out there, on par with jacketed .357 rounds, IIRC. Bullet composition is the big factor, with a hollowpoint being on the low end for penetration, up through solids, tip shape, then armor piercing rounds made out of steel or exotics. But for the most part, the Mythbusters results will be very similar in sand.

H.

tromik
09-27-2007, 06:51 PM
Considering that you can bury a still burning fire (with scolding rocks) underneath sand and never know if was there, I'd imagine it's quite good at stopping bullets.

If you know how far a bullet travels through air, and you know the density of sand compared to air, you could figure out how far a bullet would travel through sand, assuming it didn't shatter on impact.

Edit: Would different sands have different effects?

BigSlowTarget
09-27-2007, 07:37 PM
I'm going off old dusty memories here, but we filled sandbags two thirds full, and stacked them two deep for a prepared position. That was intended to stop everything up to and including heavy machine gun fire.

Damn me if I can remember what the Soviet HMG was in 86-89 though.

Googling...

12.7 x 108 mm. So a little bigger than the US Browning M2 .50 cal at 12.7 x 99mm. Anyway, the bags were basically a foot wide and two feet long, maybe three to four inches thick when filled. So yeah, two feet of bag to stop a .50 cal. Though I have no idea if it actually would, but I imagine that's something that was figured out a long time ago.

Something else, if the bags became soaked, we would have to dismantle the position, fluff, for the lack of a better word, the bags and then reconstruct the position uisng the bags from the top first. Which was just loads of fun.

BaconTastesGood
09-27-2007, 07:51 PM
The phrase you're looking for regarding weight x velocity x area is "cross-sectional density". Weight x velocity doesn't tell you a whole lot by itself when thinking of penetration.

Aeon221
09-27-2007, 07:56 PM
The phrase you're looking for regarding weight x velocity x area is "cross-sectional density". Weight x velocity doesn't tell you a whole lot by itself when thinking of penetration.

Best watch it, or he'll show you penetration but good.

caesarbear
09-28-2007, 03:45 AM
I'd be very surprised if an arrow could go through a sandbag. I shot arrows on a beach once, and they didn't even stick far enough into the sand to stay standing. Maybe you're thinking of kevlar?
I'd imagine an arrow can go through water much better than a bullet. If the same principle is in effect with sand, it might not be far off.

Houngan
09-28-2007, 04:41 AM
I'd imagine an arrow can go through water much better than a bullet. If the same principle is in effect with sand, it might not be far off.

It should work similarly, the problem with bullets and water is that water is a perfect expander and extremely dense, so the rifle bullets tend to disintegrate when they hit it. A steel bullet would probably penetrate very well, but I don't recall them testing that. Arrows have the advantage of being non-expanding and extremely heavy for their (thanks BTG!) cross-sectional density.

H.

CounterMeasure
09-28-2007, 08:36 AM
I'd imagine an arrow can go through water much better than a bullet. If the same principle is in effect with sand, it might not be far off.

They do. They make arrows with rotating head fins and fiberglass shafts specifically designed for fishing. I used to use them when I went gar fishing years ago.

When the arrow hits the water, the small fins on the head can rotate to enter the water at a less disturbing angle to minimize deflection. The arrow vibrates as it enters the water, and the fiberglass shaft allows it to flex better with the vibration than an aluminum arrow.

The downside is if the fish is big and hard enough (like a big gar), the arrow will shatter on impact. And then you are out 15-20 bucks for the arrow, plus dinner.

Houngan
09-28-2007, 08:49 AM
Why on earth were you eating gar?

H.

CounterMeasure
09-28-2007, 09:01 AM
Why on earth were you eating gar?

H.

Because they are easy to clean, have awesomely huge filets, and taste quite good if you cook and treat them like fajitas. When we threw a party, we used to kill 1 or 2 six-footers, and then cook them up on this big grille we had.

Gar tacos with a side of menudo is awesome.

Njal
09-28-2007, 10:18 AM
On a related note we used to learn in winter indoctrination that it takes 4 feet (IIRC) of icecrete to stop a bullet. Icecrete = sand + water + canadian winter.

Gramuxius
09-29-2007, 03:24 AM
A few feet of sandbag will certainly stop light bullets (at least I've tried with NATO 7.62). If exposed to sustained machine gun fire, though, the sand/dirt can be "dug" away quite quickly. There were some numbers on how many feet you could remove per minute, but I can't recall them. Certainly enough to not rely on sandbags in a prolonged firefight. :)

Ryan A
09-29-2007, 05:47 AM
On a related note we used to learn in winter indoctrination that it takes 4 feet (IIRC) of icecrete to stop a bullet. Icecrete = sand + water + canadian winter.

So THAT's why the rebel fortifications on Hoth were so easily overrun!

Raife
09-29-2007, 07:34 AM
So THAT's why the rebel fortifications on Hoth were so easily overrun!

The Star Wars movies weren't real, dummy. That, and they used blasters and turbolasers.