Battered Bullets: What Impact Does Bullet Setback Have on Function?
Experiment Conducted by: +Andrew Tuohy 

I have been conducting experiments relating to firearms for a number of years, some of them quite mundane and others rather unorthodox. Many of the unorthodox experiments have never come to light, either because nothing of value was learned, or because I had decided to compile their results over a long period of time before releasing the data.

One series of tests which falls into the latter category relates to what, exactly, makes guns blow up. We've all seen photos of exploded firearms and bloodied hands or faces that result from a "kaboom," or catastrophic failure of a firearm or the ammunition it fires. As a result, a lot of people exercise an overabundance of caution relating to any ammunition that "looks funny" to them - even going so far as to discard cases with tiny dents in them, for fear of causing an explosion.

While it's always a good idea to err on the side of caution when working with items that contain 1,000 times more pressure than a car tire, it's also a good idea to have an understanding of what can really cause a catastrophic failure. And my experimentation has shown to me that the common knowledge relating to this topic is entirely wrong.

Many others have performed experiments of this type in the past - my interest in the topic was piqued by a conversation with a ballistician who told me of a test performed decades ago by a famous writer. The details of the test made me immediately think, "There's no way the gun didn't blow up!" But not only did the gun not blow up, it exhibited no signs of damage.

Which brings me to the test I conducted using a Glock 22 and some Speer Gold Dot ammunition. I had observed minor bullet setback over a long period of time with this firearm/ammo combination. "Setback" is when the bullet is pushed into the case, sometimes by repeated chambering.

Armed with the common knowledge that .40 S&W was especially susceptible to pressure issues from bullet setback, and that the Glock 22 would blow up if you looked at it wrong, I set out to find exactly what amount of bullet setback would cause a catastrophic failure. 

Because I was absolutely certain that the gun would blow up, I took several precautions. First, I clamped the pistol in a vise and fired it remotely using a trigger actuating device. Second, I started with the tiniest levels of bullet setback, using a reloading die to push the projectiles into the case. Third, while firing the Glock, I made sure to put an adequate barrier between myself and the firearm. I then took seven cartridges and set them back at .005" intervals, to a maximum of .035" bullet setback.

I then fired all of these cartridges. Surprisingly, the Glock didn't blow up. Using a dye penetrant designed to identify small cracks, I carefully inspected the barrel and slide. They showed no signs of damage or impending doom. 

I scratched my head and tried to figure out why it hadn't turned out the way I expected. I was determined to find out the "zone of danger" for a .40 S&W Speer Gold Dot and a Glock 22 in terms of setback, so I set a few more cartridges back with the press and headed to the range - but not before I grabbed a hammer, too.

As I feared, the further-setback cartridges had no adverse effect, so I slowly looked between the hammer and some of the remaining intact cartridges. I set one cartridge, bullet up, on a smooth hard surface and delivered a solid blow to its face. The result was ugly - the hollow point deformed and the case was bulged a tiny bit, the bullet set back a significant distance. 

Due to the bulged case, I had to use the hammer to "ease" the slide into battery. I crossed my fingers and stepped back, then activated the trigger. 

No obvious damage.

I took another cartridge and hit it twice, then a third and hit it three times. The end result was disgusting and hardly recognizable - the cartridges were badly deformed and required a solid hit to the rear of the slide in order to chamber. And yet neither caused the firearm to blow up. I hit a few more cartridges with the hammer, but didn't have the heart to fire them - I figured the poor Glock had had enough punishment.

Back at home, I used the dye penetrant and found that the barrel and slide remained undamaged.

Why did this happen?

Well, Glock has revised the barrel since the early "unsupported chambers" which left the pistol with such a bad reputation, and they also beefed up the frame since the earliest iterations of the .40 S&W. And while certain powders, when used in .40, can cause dangerous pressure spikes, manufacturers of commercial ammunition wisely test and select powders that are not as susceptible to changes in temperature or, obviously, bullet setback.

So while I'm not saying that you should attack your ammunition with hammers, I am saying that you should not fear tiny amounts of bullet setback with commercial ammo - at least when it comes to pistol cartridges like the .40 S&W, and especially when you consider that some factory ammo has a natural variation in overall length that does not result in a dangerous condition. 

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