Ammo & Gear Reviews

Battered Bullets: Does bullet setback matter?

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By Andrew Tuohy,

I’ve done experiments for almost as long as I can remember, some of them quite mundane and others definitely fall in the outside the box category. Several of those unorthodox trials I’ve never made public, either because nothing of value was learned, or because I decided to compile their results over a long period of time before releasing the data.

One series of experiments I’ve done that falls into that unorthodox category relates to how, why, and what makes guns blow up. We’ve all seen photographs of exploded firearms and the bloodied hands or even faces that can result when things go “kaboom,” or there is a catastrophic failure of a firearm or the ammo it fires. As you might expect, a lot of shooters exercise an overabundance of caution relating to any ammo that “doesn’t look quite right” to them – even going so far as to discard cases with tiny dents in them, for fear of causing an explosion.

I don’t blame those cautious shooters. 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. However, it’s also a good idea to know what can really cause a catastrophic failure. My experimentation and testing has shown to me that a lot of the common knowledge related 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.

This brings me to the test I conducted using a Glock 22 and some Speer Gold Dot ammunition. I 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 cartridges are 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.

I was absolutely certain the firearm would explode so 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; I used 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.

Then, I fired all those cartridges. Surprisingly, the Glock didn’t blow up. Using a dye penetrant designed to identify small cracks, I inspected the barrel and slide thoroughly. Neither showed any indications of damage or impending doom.

Initially, I couldn’t figure out why the test 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 on top, 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 was 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.

What do you think? Is this something you’d like more details about? If so, let us know. If there is enough interest, we’ll publish an in-depth LuckyGunner Labs post detailing more experiments related to chamber pressure.


Andrew Tuohy is a contributor and experimenter for LuckyGunner Labs. You can see more of his work at LuckyGunner’s Google+ page.


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