Anatomy of a Blow Up

Gunsmiths are often asked quite a few questions concerning gun safety. One concerns the safety margin built into a modern rifle. I have a good idea, but I am not going to contribute to the delinquency of a handloader. I have inspected quite a number of damaged or blown firearms. Without exception, they were ammunition related. Just the same, some blowups are related to what I call an "accommodating chamber", one relieved too much and which allows too-rapid and too-extensive cartridge case expansion.

These chambers may not necessarily lead to a firearm blow up, such as when a cartridge case ruptures and allows gas into the magazine but without damaging the firearm. It’s worth asking the shooter for their opinion of what caused the incident as apart of your diagnosis. A blow up can be very subjective and this is especially true if the situation may lead to a court case. To illustrate, let’s look at several of the incidents I have encountered.

Although I am confident I understand what caused these blow ups, I can not be completely certain what actually happened as I wasn’t there and only evaluated the result. In one case a customer brought in a Kimber Custom II for a trigger job; a nice pistol, well finished, and it didn’t require much work to have it in top form. I fired a single round of the customer’s supplied ammunition and the firearm kicked much more than expected. I foolishly fired another round.

It again functioned well but there was tremendous recoil. I ran a third round over the chronograph and recorded a speed of 1202 feet per second— stout even for a 45 Super! This was a good 200 fps over what I would expect from a 230 grain JHP at +P level in the 45 ACP. I used a bullet puller to break the load down. The projectile was a 230 grain Horandy XTP. Along-standing standard +P loading for this bullet weight generates 1000 fps average.

I checked with the owner and his quoted powder charge of was correct for a +P. The problem here—and we have to learn something about ammunition and handloading to really examine this problem—was that the overall loaded length was much shorter than the prescribed 1.250 inch. Definitely error by the shooter made while handloading. The spent cartridge cases were recovered and demonstrated flat- The sidewalls usually give first. tened primers, a sure sign of excess loading.

All of the handloads were pulled and the shooter corrected the overall length problem. He was lucky. Would a lesser gun than the Kimber have blown up? Who knows, but the next Kimber may have broken into pieces. Despite modern manufacture, every pistol isn’t molecularly identical to the other. My bet is on the Kimber, however. I think that a simple answer to what blows guns up is that the pressure or burning gas is constrained, it cannot bleed off as quickly as it needs to.

When pressure begins to build, bullet pull is important. The bullet must have sufficient pressure—referred to as bullet pull—to contain pressure long enough for the pressure to build. Otherwise there will be erratic ignition. For example, this is why a 110 grain 357 Magnum bullet cannot be driven as fast and accurate as a 125 grain bullet. If there is any type of obstruction the pressure stops moving and must go somewhere.

If it burst the case that is one thing, but if the case is adhered to the chamber while remaining intact and the bullet is still in the barrel with pressure beyond specification, the barrel may burst. This generally occurs with rifles more than handguns. One problem is using a charge of fast burning powder rather than a charge of slow burning powder in a revolver. Fast pressure curves and a heavy bullet that slows movement is a recipe for a blow up. Older ammunition is always suspect.

As an example, I examined a vintage 351 Winchester rifle. All was well, and a limited amount of firing showed the rifle

was in great condition, however, several cartridge cases had split on firing. The ammunition fired every time and the rifle functioned but by my estimate the ammunition was about seventy-nine years old. The correct answer was to tell the shooter to stop firing that ammunition as some of the cases had split, and there is always a chance for a worse split or head separation. There is also the chance of overpressure loads in older firearms.

Even if they were fine to begin with, temperature changes may change how the powder develops pressure. Obviously, black powder firearms should be used only with black powder cartridges or those rated as equivalent. Even modern ammunition isn’t as reliable when it comes to steel case loads. One common problem is misinformation from the Internet. Folks with older 8mm Lebel and 7.62 Nagant revolvers are told that they may fire various revolver cartridges of .32 caliber in these chambers.

Sure they split, but the cartridges aren’t very powerful and it is safe— so they are told. Nothing could be further from the truth! Any time a case cracks it is bad news. Another problem actually instigated by advertising is the "accommodating chamber" of the 9mm Largo. Only 9mm Largo should be fired in the chamber. The 9mm Luger may move too far into the Largo chamber and might burst. The 38 Super is far too powerful for the 9mm Largo.

A second example, This blow up occurred with along time shooter I would characterize as a careful handloader. He was firing a High Standard 1911 45 ACP manufactured by Armscor. He fired several Far They are suspect at the least. shots and then it happened: the cartridge case head shredded, blowing into the magazine well. Thankfully, the shooter had glasses on, but he received brass to the face.

The shooter was not badly hurt but his face was pocked (his wife picked the brass out with tweezers) and his hand was burnt with powder. The magazine was wrecked and the baseplate, spring, and follower were never found. The pistol was brought to me along with a few rounds of ammunition both from the magazine and the remaining box of ammo used. The High Standard 1911 wasn’t damaged, only the slide stop was pushed out and it clicked back into place.

I thought the ejector was loose but the owner said it had always been that way. The frame was blackened. I examined the ammunition that was found laying on the ground. One had the bullet jammed back into the case. It was also blackened by powder and I felt the force of the explosion could have forced the rounds back into the case. The others appeared normal. I pulled the bullets and the powder charge was fine.

While gun powders are difficult to identify by eye, but these loads appeared to match the shooter’s powder samples. However, when I went to examine the box of handloads I discovered I could push the bullets into the cartridge case by finger pressure. There was insufficient case mouth resistance. It appeared the shooter failed to Far Pressure was at a dangerous level.

A shooter purchased an older Colt 1911, fired a 38 Super, and the case exploded, more or less. The pistol was marked 38 Super but the barrel was chambered in 38 AMU, a rimless 38 Special intended for lower pressures. apply a proper crimp. Taper and roll crimps for automatics and revolvers differ. In this instance the culprit was handloading procedure. During the feed cycle the insufficient crimp let the bullets be pushed into the case, resulting in a tremendous rise in pressure and a blown cartridge case.

I put the pistol back together. Anew magazine was needed but the magazine catch was not damaged. The barrel, chamber, and feed ramp were all were undamaged. The pistol was cleaned thoroughly. Under magnification there were no cracks, not even any deep scratches. I placed the piece in a fixture I have used for years and stood behind a barrier and fired by remote attachment with along pull rope. The pistol fired and locked back normally. In this instance all of the force blew downward and the handgun was not damaged.

A clean bill of health! I have also examined two blown 10mm pistols with polymer frames, both with handloads. The owners had been loading for the 10mm Delta Elite with seems to have had issues with longevity, largely due to the earliest recoil rod and spring designs. The Glock will run forever perhaps, but it can not stand the same loads as the Colt and were wrecked by loads used in the Delta Elite with no problem.

The same situation occurred with a shooter using a heavy 260 grain 45 ACP bullet in a Springfield without issue, but the same loads cracked the locking block of his 45 ACP Glock. A different case involved 10mm loads that had been used without issue in a different gun but cracked the frame of a XD Series 10mm. Luckily, Springfield was able to refurbish that pistol with anew frame. The SIG P220 has a rather unsupported chamber.

In the days when the Speer 200 grain JHP with its stubby nose and huge cavity would not feed in any unmodified 1911, the SIG ran it well as well as many thousands of rounds with factory ammunition. However, the SIG, some Glock pistols, and

others feature chambers that don’t offer optimal support. A factory chamber may be said to offer full cartridge case support if it supports the case 0.05 inch into the case above the beginning of the extractor groove. I prefer a chamber supporting the cartridge case well down to the extractor groove. Some pistols feature a relieved area that makes for reliability with any type of bullet nose—what was once referred to as "exotic shapes".

While there are very few instances with factory ammunition, using old load data with heavy SWC bullets or light bullets at high velocity into the unsupported chamber era has resulted in several spectacular blows. One SIG was an unusual example. When the shooter brought the piece to me for examination it was long after the fact. The spent cartridge case had not been retrieved and the blow up resulted in the right grip panel being damaged with the top of the grip panel blown completely away.

A trigger return spring was damaged and the magazine blown out the bottom and not retrieved. The shooter had been shook up and didn’t pick up the ruined magazine or the spent cartridge. The case had been cleared on the spot and the shooter stated—with imperfect memory—it was easily cleared from the chamber. The magazine release was not damaged, surprising when you consider that the magazine was torn from the lock. The frame was cracked. I thought the location was odd.

The SIG features a steel insert of a frame block that isolates steel from aluminum as the pistol operates. I would have thought it would crack near the chamber or crack around the magazine catch as the magazine was bolted from the latch but the crack is higher than the magazine latch. The shooter brought the pistol in for an evaluation even though someone had told him to put the pistol back together with anew set of grips and springs and shoot it. I replied very much in the negative.

A pistol is a machine of irreducible complexity. With one part broken the rest will not work. There is a certain amount of flex in a frame (steel, polymer, or aluminum) and this flex cannot cycle correctly with a crack in the frame. There was some discussion of perhaps putting a 22 Long Rifle conversion on the frame but I advised to scrap the frame and mark it off to a lesson learned.

If welded the frame he could not ethically ever sell or trade the piece and probably would not be comfortable firing the pistol after his earlier experience. Handgun blowups are not terribly common but neither are they rare. We usually don’t have a chance to caution shooters before they make a mistake. When working with a blown gun let caution be your guide. Most should be scrapped and mined for the parts. AG