Boomerite testing

This weekend Barb and I did some testing for a new Boomerite recipe. We ground up some Styrofoam peanuts in the blender. We blended the Ammonium Nitrate until it was a fine powder. Then we used the usual masses of the AN, Potassium Chlorate, and Ethylene Glycol. We added about a cup and a half of the ground Styrofoam and mixed it all together.

The result looked like this:

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That is 300 grams of the mixture which nearly fills the 4”x4”x2” box. It takes 400 grams of conventional Boomerite for the same volume. The hope was that the finer particle size of the AN would result in a more rapid and complete chemical reaction. The AN is usually in prill form. When finely ground it does not detonate easily.

Our hypothesis is that the prills create air gaps and the supersonic shockwave from the bullet compresses the air which heats the chemicals to the required temperature for detonation.

The hypothesis being tested was that the Styrofoam would supply the “air gaps” and enable the detonation in the usual fashion.

As you might expect for the last day of November it was a bit on the cool side at Boomershoot Mecca. Barb’s clothing confirms that suspicion:

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We took the test and control targets to the Boomershoot site and shot them with Stinger 22LR from 23 yards away. The two out of two conventional Boomerite targets detonated with a single hit. Zero out of six of the Styrofoam “enhanced” targets detonated. I then tried shooting them with 55 grain FMJ .223 American Eagle ammo from 23 yards away. Two out of ten detonated. Many of the others were “smokers”. They were close to detonating but weren’t quite over the threshold.

Barb finished off the four remaining conventional Boomerite targets with one shot each.

There are some other tests we could do along the same line. It could be we had too low a density. Packing the targets some might make a difference. We also have some hard polystyrene pellets (used for stuffing dolls, etc.) that might replace the prills. But I’m concerned they would not be consumed in the reaction and would be scattered all over the field. I expect the ground Styrofoam would just be fuel for the excess oxygen in our Boomerite mix and we wouldn’t have to worry about the potential for litter.

11 thoughts on “Boomerite testing

  1. Based on your hypothesis, the effect of the shock wave from bullet impact could be enhanced if the mixture was not loose fill. Air – the space between the prills – is compressible. Were the active mass compressed, such as in brick form, most of that compressible air would be removed and the bullet’s shock wave more directly transmitted through the active media.

    I doubt cardboard boxes are strong enough to keep the mass compressed, but some sort of binder might work. The plus of that approach might be to eliminate the need for cardboard boxes. Alternatively, does anyone make very strong shrink wrap?

    • We know that we need some air for detonation to easily occur. Regardless of the mixture detonation gets difficult when it is tightly packed.

      There must be some lower limit (too much air) on the density. I sort of wonder if we reached that with the Styrofoam mix. Perhaps packing it to the correct density would yield better detonation. I wonder this because the density was lower than that of the usual mix. We could easily compress it in the cardboard boxes to get the same or even higher density.

      It turns out the boxes do provide a surprising amount of containment. The strength of the container is not as relevant as the mass. Do the math for the dynamics of 100s of thousands of PSI events that happen at the 10s of microseconds scale.

  2. Joe- 

    I’d suggest you contact a boat yard or art supply house and get you some micro balloons. They sell these to mix into plastic resins to reduce density and make the hardened mass more easily shaped or sanded.

    Alien-

    A more densely packed high explosive can shoot at a higher velocity, as well as having a higher energy content per volume- If you can still detonate it!

    In some types of high explosives, a certain amount of air spaces are needed for the explosion to propagate easily. Also, in some primary explosives (such as Mercury fulminate) pressing to too high a density will render them incapable of detonating at all- google the term “dead pressed”.

    So, with some types of explosives such as plastic and PBX, manufacturers strive to remove all air bubbles and make them as close as possible to their theoretical maximum density, thereby achieving the highest speed of detonation and best performance. This usually REDUCES their sensitivity to initiation- A loose mass of PETN or RDX crystals shoots a lot slower than the high density SEMTEX or PBX made from the same powder, and also requires much less in the way of detonator or booster to get it going.

    Other families of explosives such as blasting gelatine and Ammonium nitrate  based water gell/slurry explosives REQUIRE a certain ammount air bubbles to propagate the detonation at all.

    Freshly made samples of old fashioned nitroglycerin/nitrocellulose blasting gelatin have a lot of tiny air bubbles and are quite cap sensitive. As they age, the air bubbles disappear and they get harder to initiate. 

    TOVEX and some ammonium nitrate/water explosives have air deliberately “whipped” into them during manufacture, and may even have foaming agents in their formulations to enhance this air entrainment . Other formulations have a percentage of hollow glass or plastic “micro balloons” mixed in to achieve the same end. The tiny air pockets, bubbles or balloons are thought to focus the shock wave in the same way as the air space in a hollow charge does, creating a myriad of little “hot spots” along the shock front, enabling the HE to reach a cap sensitive condition or require less of a booster charge-

    Explosives engineering is fun!

  3. As the real experts above described, you don’t want air or other compressible materials to be propagating your shock wave, as this decreases rate of ignition.

    Back in the 90’s I worked on hard carbon and diamond synthesis in a government lab. Among the trivia I learned was that diamond powder with grain sizes of 100 to 1000 nanometers was readily produced by means of exploding some specific materials. Made on an industrial scale by the Russians who discovered this method, the diamond powder was mixed with explosives to increase the speed of the shockwave propagation through the explosive upon detonation. Faster shockwaves meant more ignition, less waste of explosive during detonation, and a more forceful explosion overall.

    Some military and commericial explosives use this material mix now.

    So if you can find a barrel of diamond powder for sale at reasonable prices, I’d suggest you try mixing some in to your materials to see what happens.

    Good luck!

      • It is a strange and wonderful world we live in these days, where the only limits to the bizarre things you can find are the hours in the day to read about them all.

    • That’s a rather spendy explosive ingredient, looks like about $1.00 per grain (64 mg).

      Those powders are intended for polishing and sharpening- if you’ve got a flat blade like a chisel or plane iron, try some! Use a sheet of ground plate glass with the finest wet/dry paper you can get as a sharpening stone first, with a roller fixture to maintain angle. When you’ve got the primary bevel formed, then very slightly increase the sharpening angle, remove the paper and put a thin film of oil on the glass with the tiniest sprinkle of that ultra fine diamond powder on it, and polish the edge. This is how the blades biologists use to cut samples 1 cell layer thick for microscope slides are sharpened. This is SCARY sharp… You won’t believe it until you handle a blade that sharp.

  4. Thanks, Bert. I had no idea air bubbles were an integral part of making explosives perform.

    And, I think I’ll try the diamond powder sharpening thing on my hand plane blades and chisels (probably wasted effort on the chisels, they’ll lose the micro edge quickly, but I can’t get my wood carving knives too sharp..). I see that Amazon has 1/4 micron powder, labeled as 100,000 grit, 5 grams for $10.

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