The awesome power of Boomerite

A Boomershooter sent me an email with pictures of a target he wanted to bring to Boomershoot 2011. The intent is to give the shooters something more challenging to shoot at. To be specific he wanted a 1.5” reactive target at 700 yards. The concept was a steel plate on the front with a 1.5 hole drilled in it with a open topped steel box on the back to hold a normal Boomerite target right behind the hole. On top of that box he wanted to put a baggie filled with chalk dust. The explosion should then result in a yellow, red, or blue cloud of chalk dust.

I told him I he could bring it but that it would be destroyed by the first or second use. The explosion would rip the box right off of the back. He almost could not be convinced. Here is some of the conversation:

Joe: “I’m fine with your chalk dust dispenser if you don’t mind picking up the pieces if it spontaneously disassembles.”
Boomershooter: “we got it covered . . 1″ plate with 3/8 open topped box . . i will weld it myself so i don’t have to worry about bill’s welds scattered over the hillside…”
Joe: “My guess is that you will be lucky if the welds hold for two successful hits. Just one is my guess.”
Boomershooter: “i challenge you to be the one to break my welds…”
Joe: “My guess is the .250 chamber will be ripped in half after the first or second detonation. You are welcome to try it as long as everyone is at least 300+ yards away from it.”
Boomershooter: “i’m thinking your 4″ 375 yard targets are going to be a walk in the park for this high tech explosive containment device. i’m sure if you packed it solid you might get it to bulge. but enough explosive to send a colored cloud is what we are looking for…”
Ry: “I admire your faith in your product.”
Boomershooter: “been a certified welder for 35 years . . when i see people shooting bowling balls out of a 1/4″ thick argon bottle over a mile, i figure it can’t be bad with no pressure build up at all . . “
Ry: “My experience was this: I put a little boomerite in a mountain dew bottle (call it a half liter), put the bottle on the round. A couple inches behind it, I put a railroad tie plate on edge. The tie plate landed about 75-80 yards away and was bent into an L shape.”
Boomershooter: “oh well . . you will be getting the explosion test dummy in a couple days . . we will find out after that…”
Joe: “There will be a LOT of pressure build up. I’m expecting pressures beyond the tensile strength of steel. The maximum (of course it is confined instead of partially open) of ANFO is about 1,500,000 PSI. Partially confined it can still reach 1/10 that. We are pretty sure our mixture is more powerful than straight ANFO. If we were to fill the box with Boomerite we could see the total force attempting to separate the tube from the plate reach a peak of (4” x 6” x 100,000 PSI) or 2.4 million pounds.You know your steels and welds better than I do, but my bet it is going at least bulge on the first shot if not get ‘opened up’.”
Boomershooter: “well . . one low tech target is on it’s way . . you scared 223 bill with the 2.4 million pounds of pressure fact, so he elected to add a plate to the back of the tube to keep the bullet from penetrating the back of the tube. give it a try and let us know what you think.

The target arrived earlier this week. It is an impressive target. It weights almost 50 pounds:

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While out blowing up the snow castle we tested the target as well.

We mounted it on some 3/8” rebar. It was intended to have something much larger and we couldn’t tighten up the bolts properly. Hence it hung really crooked:

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We then put a very small charge of Boomerite in it. Just about 1 cup—200 grams. This was in a zip lock bag that was poked through the hole:

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On top of this we put another zip lock bag with 600 grams of chalk dust:

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We then got back 100 yards (I figured that with such a small charge and part of it even sticking out the front we would be safe) and shot it with a 50 gr VMAX bullet:

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We should have used yellow, red, or orange chalk dust to give better contrast with the snow. But you can tell there is definitely a blue cloud in the air.

But what happened to the chalk dispenser? It wasn’t visible to the naked eye from 100 yards away. We walked up to where it was and found this:

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The target had been blow backward until the rebar had bent almost in a U and the target was touching the ground underneath the snow. Notice the rectangular outline on the bottom of the target? That was the bulge from the Boomerite containment box. Do you remember he said, “i’m sure if you packed it solid you might get it to bulge”? This was FAR from packed solid.

Now let’s look at the sides of the containment box:

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One dead target.

20 thoughts on “The awesome power of Boomerite

  1. We really need to put together a fund drive for you to aquire a high-speed camera and some appropriately, absurdly thick lexan for it…

  2. Decent cloud – definitely different from the normal one, hence easily identifiable. If the “bucket” were angled (wider on top) and the chalk-dust either lower in quantity or positioned further up/away, it would not act as tamping nearly so much(which is what it is as far as the explosive is concerned), reducing the effective containment and lower the peak pressure significantly, meaning the target would last longer. Also, why is the thick plate only on the front? If you’ve got the thick stuff, use it all around.

    Hmmm… Random pondering- the target got bent over backward pretty violently; was the main rearward force from the blast upward being re-directed backward because of the relatively frontal mounting of the rebar, or from the boomerite jetting out the front hole like a rocket motor pushing back? Got any close-up pics of the frontal hole after testing?

  3. I cannot figure out the need for containment. Why doesn’t he just put a shelf supported by three or four vertical pieces and then tack some hooks for rubber bands at the three and nine o’clock positions far enough out towards the edges that they won’t torn off by the explosion? Or he could even drill the plate and insert bolt hooks. It is a single shot target stand, after all.

  4. Rolf,

    A thick plate all the way around would require different welding techniques. It would be quite a bit more work.

    Probably both the upward and forward facing “jets”. I’ll post pictures of the front sometime today. I have an USPSA match to prepare for and participate in first.

    Phil,

    We tried to convince him of almost that same exact thing. Maybe now he will listen.

    He didn’t say it but it would be true that the chalk wouldn’t be launched to as great a height.

  5. In all fairness, he WAS correct…The welds themselves DID hold.

    I too am a welder (of a mere 15 years experience though), and having dabbled with Tannerite (which I presume to be of similar properties to Boomerite) myself, I chortled upon first viewing the submitted contraption. I wouldn’t have tried that with anything less than 1/2″ AR-400 at an absolute minimum (for a very light load), and even then I would half expect destruction.

  6. We know from video evidence that a 7″ target shot in the front directs the blast primarily to the front and back. Extrapolating from that, I believe that the vertical vapor columns and rings seen in the “clean-up” videos are from 4″ targets shot in the side. The blast is still primarily front and back, but in these cases front is up and back is on the ground.

    We also know from Ry’s amazing moment-of-impact photo than even a cardboard box will briefly contain and channel the blast.

    With that assumption, I suggest eliminating the containment box and just rubber-banding a 4″ target on its side behind the hole, with the box cover folded back and underneath and the chalk bag resting on top. I’d guess that two rubber bands, one vertical and one horizontal, would be enough to hold it in place.

    The 1″ plate is probably thick enough to last, even at the tree-line. Here is a picture of my 15″ diameter, 1.5″ thick mild steel target with two hits each from 300 yards of 30-06 (left and above center), .338 Lapua Magnum (right and below center), and .50 BMG (right top/bottom). The .50 BMG rounds were standard military ball (5 MOA) and left craters less than 1/2″ deep.

  7. I know nothing about the physics of powdered explosives, but in true internet fashion, that won’t stop me from holding forth.

    Is there something equivalent to the Misznay–Schardin effect for powdered explosives? I would be looking into research in that direction, or, failing that, try a parabolic powder cavity not completely full (per Phil’s comment on tamping) with the dust container sitting on top of it. Though upon reflection, I don’t know how you’d ignite the charge with that configuration. Perhaps the accuracy challenge would be to hit a separate plate which actuates a detonating device.

  8. Scott,

    I like your suggestion.

    Jed,

    We have observed that the majority of the blast is indeed perpendicular to the surface of the “sheet” (our larger targets are similar to a small pizza box).

  9. sweet . . now that i see that i need the hole all the way through to counteract the front hole blowing it over backwards, and it was the square corners of the factory tube that split, target test dummy number two will be heading your way in a couple days. having the first attempt fail is not embarrassing, but not being able to hit the 1 1/2″ hole at 700 yards might be…

  10. Everyone’s thinking inside that little steel box. If the objective is to have a 40mm boomer, build one, put it on a stake, and shoot at it. If the second objective is to have a color display instead of the plain white cloud, pyrotechnic manuals tell us what chemicals to add to the boomerite to achieve that. No need for all this steel, built to some magical spec which will resist a gazillion psi. Build a smaller boomer, make it go off in color, make it a “smoker” rather than a ka-boom target. The military has been building fine smoke grenades, in different sizes, some as small as 40mm, for decades. This is mill-run stuff for a pyrotechnician, you guys must know one from somewhere.

  11. the whole purpose of the containment is to direct the colored chalk straight up, like it did. i am very pleased with the look of the boomer. i want it to look different than every other boomer on the hill, and it would let everyone know you hit a more difficult target. as for not going heavy all the way around, it weighs 46 pounds already and i’m too darn old to pack six of these up that steep hill. those four 1 1/4″ plate gongs we packed up there the last two years taught me that heavy sucks.

  12. I, for one, applaud the effort. I like the effect of different types of pyrotechnics goind on and if the holes were differenct sized for each color of chalk, it would provide even more entertainment.

    Figuring out the containment vessel is the hard part, but don’t let that stop you!!!

    Bill

  13. Yeah; they don’t launch bowling balls using high explosive as a propellant. You can fire your 300 Win Mag, or your 18″ ship’s gun, all day, but put something much faster in there and she’ll let go into high velocity shards. What was that quote you had on here a while back? Something like; “the tensile strength of the material becomes irrelevant…”

    Having been with Ry on the day of one of those railroad plate experiments (oh, and that was not your everyday tie plate either – that one was super extra heavy) I would not have wanted to be within half a mile of that target holder contraption. Seems more to me like the shooter is downrange from the “target”. So long as no one got their head taken off, I guess it was a good day though. Carry on.

  14. Lyle,

    This was a very small charge compared most of the stuff we play with. And the small mass pieces were on the far side of the much larger target face. The physics made it such that I couldn’t see anything heading our direction for more than a few yards unless the target face ruptured. I just couldn’t see that happening. And even in the vertical direction everything pretty much had to go down except for the chalk. And that is what happened. Everything metal went back and down and the chalk went up.

  15. Yeah; I figure that if you were there, there really wasn’t much of a hazard. So I admit to being a little melodramatic. But still, Kids; don’t try this at home. Really.

  16. I second the suggestion to add other metal salts to the explosive charge. NaCl for yellow, LiCl for red, borax for green. Pyrotechnic colors aren’t just for fireworks, are they?

    As for the metal box target: If you want a differently shaped cloud of chalk, how about a metal box with a hole on one face, but open at both top and bottom? Use a cardboard insert in the bottom to hold the boomerite, with chalk atop the explosive. The explosion will propagate perpendicularly to the plane of the boomerite, even if the baggie holding it is 1″ thick, mostly blowing “up” and “down” instead of into the metal box walls. And the target might be more or less reusable, even if it bends a bit. As a bonus, with less metal in the box, it will weigh less, and take fewer welds to complete.

    I think a quick patent application is in order. Then all I have to do is drive up the sales numbers, and launch the IPO on my “improved” boomer chalk boxes. I might even be able to afford to learn to shoot well enough to attend a Boomershoot….

  17. Very sweet. I think Rolf has a good idea. Both the back and sides should be narrow at the bottom and wide at the top. It shouldn’t be hard to cut the back and side pieces in a V-shape before welding. Then the forces are angled up and out on the back and sides. I like the thicker front so when it fails it blows apart in a safe direction.

    Have fun with this one until you blow it apart.

  18. You could make the box look like Swiss cheese. Tape the bag of boomerite right behind the hole. Put chalk dust into an old bean can with the top cut off. Mount the can onside the Swiss box on an upper inside corner. The can will collapse and dust should be blown up. Or the can will launch. Either is fun. Take pictures.

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