Another column on the spreadsheet

Years ago Ry coined a phrase we use when we are perplexed by something we thought we understood, “There aren’t enough columns on the spreadsheet.” This is usually used in the context of Boomerite.

Last week I realized there was another column on the Boomerite spreadsheet. Ry and I then chatted about it a bit and came up with a test plan. Last Friday I mixed and boxed three different recipes and performed the first set of tests.

The story is that we know Boomerite goes, essentially, dead after a week. But we don’t know the rate at which the degradation in sensitivity occurs. Because the quantities involved we make the targets for Boomershoot over the course of two days before the event. Most of the Friday production is used in the High Intensity, Precision Rifle Clinic, and Field Fire events (maximum range is 375 yards). Most of the long range (up to 700 yards) targets for Sunday are produced on Saturday. We expect targets which are one day old to still be close to the maximum sensitivity but we have never done detailed tests on one or two day old targets.

My epiphany last week was that when we have adjusted our recipe over the years we always tested the detonation sensitivity within a few minutes of when we mixed it. We were optimizing for maximum sensitivity for targets which had aged only, say, 10 minutes. What we should have been doing was optimizing the recipe for maximum sensitivity of targets which have aged for one or two days.

On Friday I created batches of Boomerite with various amounts of Ethylene Glycol while keeping everything else the same. The recipe we have been using for years uses 45 mL of EG. So I made targets with 35 and 55 mL of EG to test along with the usual amount.

I then attempted to detonate them with my .22 shooting CCI Stingers at various ranges. The 32 grain bullet is moving fast at the muzzle but it slows down quickly. By changing the distance from the targets I can get an estimate of the velocity required for detonation. Of course the velocity required for detonation is also very dependent on the bullet shape. Just because the hollow point Stingers detonate at a particular velocity doesn’t mean that the much more pointed bullet like this Woodleigh VLD 50 BMG bullet will detonated targets with the same or even significantly greater velocity. Here are pictures of the two bullets:


Yes, what I am saying is that both the bullet energy and momentum at the target are almost irrelevant in making the target detonate. For any give bullet type it is velocity dependent. For any given velocity the more pointed the bullet the less likely it is to detonate the target. We have literally seen multiple .50 BMG holes in a target while nearby targets hit with a .308 detonated reliably.

But since I’m using the same bullet we should (how many more unknown columns are there on our spreadsheet?) be able to determine the sensitivities of the different recipes over time.

The test results were “interesting.” All tests were done at a temperature of 33 F.

Within a couple hours of being mixed all recipes would detonate at 23 yards with a single hit from the Stingers and none of them would detonate from 29 yards. This figures out to about 1370 fps and 1330 fps.

About 26 hours later, after being stored at about 70F, none of them would detonate from 15 yards (~1425 fps). However they would all detonate with hollow point .223 rounds from about 20 yards away.

If the recipes made a difference my test did not reveal the difference. The deterioration while in storage is affected by still another column on the spreadsheet. My next hypothesis is that it is temperature dependent. I need to store a batch of our standard recipe at two different temperatures, say 30 F and 70 F for a day and see if there is a difference in sensitivity.


19 thoughts on “Another column on the spreadsheet

  1. Your Design of Experiments sounds delightfully productive. So far I see EG concentration, storage time, storage temperature, bullet velocity, bullet shape, bullet size. And those are only the columns you discussed above.

    Your composition of ethylene glycol is of interest to me as a former, lapsed chemist. Are you using pure antifreeze or premixed-with-water ready to use antifreeze? Could water from the EG make a difference in stability, or is it air exposure that kills the sensitivity of Boomerite?

      • Distillation to obtain more pure EG would be a pain, but I assume it could be done, just as an experiment. Sourcing pure EG is likely possible, but would also likely be more expensive. Cost is one of the existing columns on the spreadsheet.

  2. Since I don’t know the exact composition of Boomerite, I can’t say exactly what is happening. But I assume that it contains a nitrate salt of some sort in the blend.

    The chemical half life of nitrates in an aqueous environment is about 2.5 hours, at least from one reference book.

    From a chemical perspective, the ethylene glycol is a humectant and will attract atmospheric water into the mix, as well as having water as part of the mix itself. Pretty much all glycerin derivatives share this property, which is why they are are used in everything from skin care products to cigar humidors.

    If your goal was to create an explosive with a built in safety time limiter, ethylene glycol was a very good choice.

      • I’ve reviewed the formula. Basically an ANFO variant with a chlorate booster. There is some very interesting chemistry going on there.

        How do you store the ammonium nitrate prills? They are hygroscopic on there own and when I’ve encountered them in the past, they were stored in bags, not airtight drums.

        But no matter the method of storage there, autmotive grade antifreeze will have water in it, which will degrade the effectiveness of boomerite over time because of the way chlorate reduces to a salt (KCl in this case) and oxygen, with water going on to catalyze the reaction in another molecule.

        I wish I could be actually helpful, I’m sure you know all this chemistry.

        • I was not aware that the water was a catalyst to KClO3. That could explain things. It also suggests that if we increased the amount of KClO3 we might retain the sensitivity for a longer period of time. It would also mean storing Boomerite at a low temperature will slow down the degradation.

          The AN is stored in the bags we purchased it in. As near as we can tell the mix works just as well whether we use AN purchased five years ago or five days ago. It doesn’t appear to pull moisture from the air in our environment.

          Thanks for the info.

  3. IIRC the hypothesis is that Boomerite is hygroscopic, and degrades in sensitivity as it absorbs moisture. Have you tried adding a dessicant to the mix?

    • No. I’ll look into that. Since the AN and KClO3 are hygroscopic my guess is that we will need to mix the desiccant in with the Boomerite rather than drop a small packet of silica gel into each target.

      I wonder if we could mix the desiccant with the ethylene glycol then add that to the other ingredients. Or would the adsorption (not absorption) of silica gel pull in the ethylene glycol just as well as the water?

      Both silica gel and calcium chloride are easy to get and relatively cheap.

      • Silica gel is very likely to affect the explosive properties — after all, isn’t dynamite basically nitroglycerin plus a porous desiccant-like material?
        Could you seal the charges in plastic with a heat-seal machine? (Would that be a hazardous operation?)

        • We used to seal it in zip lock bags. Now we use heat shrink plastic. Because of this it can’t really be a matter of moisture from the air over time. If it is water catalyzing the KClO3 to KCl + O reaction then it must be the trace amounts of water in the ethylene glycol and ammonium nitrate that is doing it. Hence, we need something in the mix to pull the water from the other components.

          As far as changing the explosive properties small amounts of something essentially non-reactive shouldn’t be a problem in this application.

  4. I wonder if the bullet choice is why I was having more luck last year with a 308, then others, because I was using a soft point 180gr hunting load, and most others were using VLD ~155gr loads?

    • On the other hand, the gentleman I attended Boomershoot with had the best success of the week (for us) with .223 A-Max bullets, which are about as pointed as they come (as a whole, that is).

      I wonder if the paper/plastic shell of the Boomers is enough to cause the plastic to start deforming the rest of the bullet, or if that was just sheer, dumb luck…

  5. The antifreeze will lose some of its cost advantage, and possibly slow down the process, if it turns out you have to dry it somehow. Another tack would be to look for an alternative ingredient.

    • $68/liter isn’t expensive? That would make it nearly 80% of the cost of Boomerite. Boomerite would then be essentially the same price as Tannerite.

  6. Speaking from my experience with OTHER ammonium nitrate based HE’s-

    Air bubbles in the mixture are a sensitizing agent. After mixing, if air bubbles tend to work their way out of the mix on standing, the mix becomes less sensitive.

    A possible test of this? If you have access to a vacuum pump? Box up a boomerite charge. Pull a vacuum over it (bell jar, refrigeration maintenance type pump) while vibrating the container with something like a vibratory sander with no paper on it for maybe 10 minutes. After doing what you can to eliminate air bubbles, take it out and shoot it immediately.

    If artificially “aging” by air removal desensitized the target, try adding phenolic “micro balloons” to the mix and see if THAT prolongs sensitivity…

  7. Here’s an example of the plastic micro balloons:

    Some blasting emulsions use air bubbles whipped into the mix as it is pumped into the bore holes, along with thickeners like guar gum to keep the bubbles where they are at until the time to fire the shot.

    Other formulations, including varieties that are factory mixed and packed in plastic skinned “sausages” may have such micro balloons mixed into the water based nitrate slurry along with thickeners, cross linking agents & etc. to ensure sensitivity over a prolonged storage life.

    Lots of ways to trick ammonium nitrate into being more sensitive!

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