Detonation

Almost a year ago as I write this, in the July 2002 issue of Rifle, I made some comments in my “Spotting Scope” column regarding the misuse of the word “detonate.” At the time, I had read a few reports of incidents where a handgun or rifle (used mostly by cowboy action shooters) was destroyed, or at least put out of service, because of what the user “claimed” was a powder detonation.

Since my formal education consists of a liberal dose of engineering and physics, these false claims set me off. It was, and still is, a classic example of someone, who had no idea what happened, copping out to the most readily available excuse - blame it on the ammunition. Never mind that the guy who made the handloads disavowed any responsibility for operator error at the loading bench.

I suppose the one thing that was the most irritating regarding the so-called “detonation” theories that were floating around on the Internet and in printed material was that no one offered one single scientific fact to support their conclusions. It was, and is, just plain, old baloney.

So, I made a bunch of phone calls to folks in the industry about the so-called detonation theory. Not one single professional in the business of making/selling gunpowder or ammunition believed detonation could be the cause of the reported mishaps. I also understood that by reporting that fact, I would probably receive a whole passel of letters from folks claiming that the industry people were just out to cover their backsides. What I did say in that column, however, was that factory loads don’t blow up firearms, handloads do. That was backed up by the multitude of responses from powder and ammunition people. I have yet to receive a communication from anyone claiming a factory load blew up a gun of any kind. But, we still have folks claiming to have blown up firearms with handloads. Now I don’t know about you, but I find that simple fact quite interesting.

Not long after that column appeared in Rifle, we received a letter from a reader in Alabama, who outlined the conditions for a detonation. It was so well written - in layman’s terms - I decided to print it here in Handloader, which, quite frankly, is where my comments should have been directed in the first place. My error.

What follows are my comments from “Spotting Scope” in Rifle No. 202, July 2002.

“Another bunch of bunk that is flying around lately is the misuse of the word ‘detonate.’ It appears some folks who blow up guns have decided the powder is responsible, claiming it detonated, as if it were dynamite or some such explosive. Gunpowder is designed to burn at the surface, over time. Hollow tubes, like the IMR series, burn from the inside out and the outside in. Flakes burn on the opposing flat surfaces and from the outer edge toward the center. Ball or spherical powders burn from the outer surface toward the center. None of these powder configurations can - by design - detonate.”

Now read the following from our reader in Alabama:

While eating lunch today, I had a chance to read your “Spotting Scope” column in the July 2002 Rifle and noticed some statements that I felt you might wish some comments on.

The first is the extremely prevalent (mis)use of the word “detonate.” There is a very precise meaning for a detonation (something which detonates undergoes a detonation reaction) which is when the rate of the reaction proceeds at a velocity greater than the speed of sound in the material undergoing the reaction. While I could not, quickly, lay my hands on data for the sound propagation velocity in standard propellants, I did determine the velocity in the chamber gas at 60kpsig. This is about 1025m/s for a single base and about 1045m/s for a double base propellant. (Sorry for the metric units, but they make some things easier.) The velocity of sound in a condensed phase, solid, is usually higher than in a gas. So, to make things very conservative and easy to calculate, I will assume that the velocity in the solid is only about 1000m/s. If a “typical” single non-perforated propellant granule has an external dimension of 2mm, then the total distance for the reaction to occur in is 1mm. So, the time for a true detonation reaction, starting at time zero for an entire grain, cannot be any longer than 1mm/1000m/s = 0.000001sec (1 micro-second).

Enclosed is an actual time/ pressure curve for a 7mm Remington test firing. I would estimate that about all of the propellant was consumed within, perhaps, 0.001 second. This means that if a detonation were to happen it would be a minimum of about 1000 times faster.

Is this likely to ever happen?

With a single base propellant I would have to rank it as “nearly” impossible. With a double base propellant it might be “slightly” more likely, but still “nearly” impossible.

In the “dim” past, I have tried to detonate single base propellant with a blasting cap with no success. The only really big explosion of single base propellant that I know of, and I don’t really know if it was in fact a detonation, was the one that caused DuPont to leave the business.

There is something called the “critical diameter” which describes the minimum diameter that some material will detonate in, and below that diameter the energy losses are too rapid to permit a detonation to proceed. For many military explosives this critical diameter may be less than 1-2mm, and for some commercial explosives it can be more than 2 inches. While I do not know what this diameter is for a single base propellant, the DuPont explosion involved in the neighborhood of 200,000 pounds, so the critical diameter could be quite large, and a true detonation still could have occurred.

When this diameter is determined it, usually, involves what is called a strong stimulus - typically, a 10-100gram explosive booster in contact with the material being tested. This strong boosted detonation wave is then examined to see if it dies out within some distance, and if it does, the critical diameter must be larger than the diameter tested.

During a detonation of most condensed explosives, the combination of the rapidity of the reaction and the high pressures produced, commonly many 10s of thousands of atmospheres, will cause any materials in contact with them to shatter.

Another common misuse of detonate is when a standard percussion primer is said to detonate. Since we typically don’t see fired primers shattered into small pieces this is clearly not much of a “detonation.”

However, from experience, I suspect that given a true strong stimulus, a high nitroglycerin double base propellant might have a critical diameter which is small enough to detonate in a large caliber gun - such as a Naval piece.

The point being that a “detonation” is extremely unlikely to ever occur in a small arm. It would be interesting, if you are ever given the chance to examine a blown up gun where the ammunition supposedly detonated, for you to look for any evidence of shattering or spalling. I would be willing to bet a dinner at a 4-star restaurant that no such evidence is found.

The second item is the statement: Factory ammunition does not blow up sixguns or shotguns.

Here I probably agree, but . . .

In the early 80’s I was working for Action in Philadelphia, then the importer of the UZI. I had many occasions to examine guns that were sent back as “not working.” Aside from the usual, and expected, actual malfunction or broken part, there were a substantial number that had “obstructed” bores. The usual obstruction was a bullet, or for that matter many bullets. I sectioned one barrel that had no less than 11 9mm projectiles in it. (Shooters sometimes amaze me.)

The common thread that tied these together was either reloaded ammunition, or using PMC. To be fair, PMC has vastly improved since then and I feel is nearly, if not fully, the equal of the other major manufacturers. The problem, in either case, was most likely very light, to no, propellant loads in some cartridges. I don’t believe that it would be possible to double load using real production machinery, and in a 9mm probably not even by hand.

While the UZI barrel was quite thick and strong, I could easily believe that a light load, just enough to get the projectile down the bore, and then another full load following it - in a lightly constructed weapon - might lead to an ill-informed verdict of “the ammo blew my gun up.”

So, the question is, “Why do these folks blow up guns?”

First, it appears that the common denominator is reduced loads; some are below suggested starting loads recommended by ballisticians for the powder/bullet of interest. That includes using load data that was developed with a jacketed bullet and substituting a cast bullet of the same weight.

Second, a good number of these blow-up handloads were assembled on progressive loading presses. If you want a recipe for disaster, just sit down at the helm of a progressive press and fail to pay attention for one or two seconds. All you have to do is short-stroke the handle one time. Or, the powder may bridge in the measure, dumping a partial charge in one case and an overdose in the next. Or, you may fail to seat the primer properly. Or, you can get two bullets in the same case. Or, you may fail to establish a proper crimp, which with the lack of proper bullet pull, can cause a squib - which leaves the bullet lodged in the barrel. (With ear plugs, squibs can’t be distinguished from a normal load - mostly because you can’t hear it. Besides, some folks are just thumbing the hammer back as quickly as possible and a squib goes unnoticed.)

Bear in mind in handloading, anything that can go wrong will. Just about the time someone thinks they have it all figured out, and declare themselves experts, bingo, mistakes start to occur. For my part, if a novice/tyro/amateur isn’t using loading blocks, he/she is asking for it.

Now, there is one more item to consider. Using modern firearms manufactured with the most precise technology with regard to design and metallurgy, pressure tests show it is difficult, if not impossible, to blow up a handgun with “reasonable” loads. That is, it would take a caseful of Bullseye to blow up a Ruger Blackhawk .44 Magnum that generates upwards of 100,000 psi. Which is to say, you can’t blow up a Ruger Blackhawk .44 with too much 2400 because you can’t get enough of it in the case to develop the kind of pressure it would take to lift the top of the cylinder.

Drawing from that knowledge, it would be difficult to blow up a sixgun with any load listed in any reloading manual, because the lawyer factor in modern handguns is way off the chart. So, the question remains, with that kind of strength and reliability built into handguns nowadays, why is it so easy for someone to blow the top off a Colt or one of its copies from Europe?

Frankly, I don’t have the answer, but I do know that near maximum or maximum loads don’t blow up handguns, but a number of blowups have been traced to reduced loads. At least we think they were reduced, and not a double charge of powder or two bullets in the case. The only single action I examined was forwarded by its owner who claimed the bullet hit the target, but I found a bullet in the barrel. It may be that the bullet that exited the barrel was bounced or knocked out by the bullet I found, or there were two bullets in the case - one exited, the other stopped. Either way, the combination of events lifted the top off three chambers and removed the top strap.