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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. 

To see more in-depth firearms testing and to see our selection of in-stock, ready to ship ammunition at
Jeff Horneck's profile photoNick Brainard's profile photoAce Dragon's profile photoMichael Anderson's profile photo
Very interesting I have been wandering about that, Thank You!!
Very interesting. I thought for sure any gun you put them into would have blown up.
what was the point of this ?...if u have a round looking like that ... discard
 it !!!
Very interesting and surprising. I would enjoy reading more research along these lines. 
Heh,you created the .40S&W Short. 
I'd be much more interested in this topic with both reloaded ammo and loaded ammo with new components as well.
I like it!.

I wish I could get paid to test ammo like this.  Recently I was testing out home made bullet lube recipes for my new casting hobby.

Turned out one was too slippery, jumped the crimp and the soiled propellant caused a squib load.  Being this was a LCR revolver, the bullet was stuck mid way between the brass and the barrel.  Luckily brute force with a hammer and rod tapped it into the brass case again.

Also, please consider evaluating the use of small rifle primers in pistol loads.  (so far it works for me
+Jonathan Ferris Discard?  At least pull the bullet, replace powder and re-seat the bullet.  Unless you've got an ammo tree in your yard, I'm not throwing much away these days.  :)
Very enlightening!  I find .357 Sig rounds (Gold Dots just like the author's article) will experience quite a bit of setback upon chambering.  I've been curious about what's worse - having to use that round or leaving it behind....  +1 for full report!
Joe M
You are becoming the mythbusters of guns. Keep going! For science!  I would be interested in how much setback is caused by rechamberings of a round, say 10x, 100x, and doing the test with different brands and calibers. Seems like exploding gun stories usually involve an obstructed bore and/or hand reloads.  I wonder how many of those poorly crimped hand reloads also had twice the charge they were supposed to.  The internet says aluminum and steel case setbacks more than brass, and that 357 sig setsback more than non-shouldered cases.  True?  I have no idea.
Definitely do a more indepth study of pressures.  I double loaded a round once (by accident) and thought for sure I had damaged my gun, but it was fine.
I have a few .45 acp rounds that have a finy bit of setback. Im glad I read this. Thanks
Thank you! Please expand tests and publish!!
What did you expect it's a GLOCK!!!!
Good read on your test. I always wondered on the 'slight' set-back on whether to shoot or 'redress' round with breakdown and reload. I would also hold this to 'factory' rounds as reloads can be assembled with just about anything.
I loved watching all the comments on Facebook, just how mean, and close minded people are, and how most of them played right into the story.  Most people don't know half of the stuff they think they know.  They go off of stories, and what they've been told, and never think for themselves.  I applaud you guys for taking the precautions, and questioning what people have taken as the norm over the years.

Keep it up!
"Reloads" as they are often mistermed, can and often are assembled with NEW components.  Very valuable information can be learned when you know what powder and approximate burn rates are being used.  We have absolutely NO idea what that information is with factory rounds, and provides very narrow results: it either blows up or it doesn't with no reason why.  We would need factory burn rate data which can then be compared directly with known other powders off the shelf to provide a basis for comparison at the very least.  That is if you can not afford to get a test barrel that measures CUP or PSI to evaluate the data exactly.
Love the article. I'd like to see more. maybe even a video.
because I have had a passing intrest in Kabooms for a few years one thing i have noticed and think should be mentioned is that there is a +P and +P+ itus that I think gets people into more trouble with the bullet setback than anything else.  simply put all +P+ rounds are unsafe for use  and if your using something other than a 38 spl  9mm or 45 acp  +P is also a bad idea.  the reason is that +P is only standardized for a few calibers  and as such most manufacturers do not make their barrels withstand pressure above saami specs and with no +P or +P+ specs out their your barrel is not made to withstand it.  This does not mean that your gun will blow up if you use +P or +P+ rounds in a gun not made for it the first time you shoot it, but it does mean you are dramatically shortening the life span of your gun and combined with increased pressure from bullet setback you may get a kaboom after some use.
Great article. What generation Glock were you using?
And here I've been slightly concerned about 9mm reloads with a COL .010 too short...
Just as I thought, actually using them will cause a JAM - hopefully not a deadly one as in confronting a 'burgaler'
ok, so the 40 s&w short wouldnt blow up a glock. what will? a double charge of weapon destroying tightgroup? a stuck bullet? this story is only half done. 
+John Mounce I would really like to see .357 SIG as well, and in a Glock 32, since I know that frame was beefed up even more over the 23. Really, any experiment with pressure in a bottle-necked cartridge would be excellent to see.
I'd be very interested in hearing more about this. Any time you can bust an internet gun myth, I'm interested.
This was a very informative and timely article.  Until this article, I never heard of bullet setback.  And until this past weekend, I never saw it or the potential effects.  However, in my case I had a completely different problem that was not discussed in this article.  I was using factory loaded 124 grain copper plated round nose 9mm ammo made by BVAC Ammunition, Inc. in Stevensville, Montana in my Glock 19.  Half way though the clip the slide jammed only about two or three millimeters short of completely chambering the round.  This caused a hard jam that prevented the weapon from firing and I could not clear the malfunction by racking the slide.  Apparently the setback bullet caused just enough of a bulge in the casing to jam the cartridge in the chamber.  The jam was so hard neither I nor the range safety officer could pull the slide to the rear.  We cased the weapon and took it to the range armorer who was able to extract the round by placing the Glock in a vice and tapping on the lower receiver with a soft mallet.  We confirmed a setback round caused the jam and following a visual inspection and function check, I returned to the range and finished my shooting set with no problems.  Thank you for publishing this article and giving me a better understanding of this potential ammunition problem.
A very irresponsible article.  The author makes an unspoken presumption that set back ammo is not dangerous and can be used at will.  This is far from the truth and subjects Lucky Gunner to considerable liability should someone that reads this article experience catastropic failure of a firearm shooting ammo with excessive set back or case damage.
Very Interesting.  The article mentions that commercial loaders know to use powder that is not sensitive to bullet setback.  How would you determine if a powder can support the setback and not cause excessive pressures?
Hey +Matthew Walker

That's generally something we'd rely on somebody with commercial equipment to determine. It's relatively difficult to determine without the correct instruments and tough for the average shooter to determine without significant investment. (In other words, we'd have to check with a manufacturer with the resources to determine it).
Interesting and good to know - but may not to apply to other firearms equally?  In any event I wouldn't fire any rounds looking like those - a slight setback maybe
relaod my own ammo. never have i had a gun blow up on me with a slug jammed into the case. in a 1911 , or a glock, 45 acp. now i use differant brands of powder. Vetavore powder you have to be carefull with chamber Pressures. had one round in a 44 S&W 29, cracked the wheel of the revolver. my bad. i never checked the cartrige length. i dropped it on it's head. burned my support hand. i would be more conserned about your powder messurments. 
Interesting article. Note that in addition to a potential for kaboom, bullet setback can also cause primer compound separation, which results in a failure to fire.
We get a lot of deformity in the cases in our Federal HST .40. These are carried in M&P's (duty pistols). Most of it happens from being carried in the magazines. I have also noticed the same in my Glock 26 that I recently purchased and carried. I have never experienced a failure of these rounds despite some being very dented.
reloading ammo for 20 years i had some that when fed into the chamber they fierd with alot of recoil. i have shot dented brass and i had a squib load in my 45 . thank god i dropped the mag and the slug was jammed in the barrel. i think if i did noot know what a pop was i would have came close to a blow out on the barrel. auto loaders don't need a crimp. i do a very slight crimp on 45 and 9mm. that keeps the slug from jamming in when fed. don't reload any more. no room in my tiny apartment.
Used to have some data from a powder company H******N on the 454 Ca***l cartridge. Over 20 powders and Many loads up to and over 62K CUP. None of the hot loads destroyed the rig but the test barrels are a bank vault door. What did it in and consistently had not burns, but explosions/detonations were light loads of faster powders where it left the primer vent uncovered and the round would have a flash over and the powder exposed to the primer was huge. Way back in the 60's when people shot 38 Specials at the range punching paper we had several S&W's bent with very light target loads of Blue Dot, Herco and Bull'seye so not the powder, but all we did was up the loads and all was good. Wish we had had the info in the 60's it would have saved some nice pistols. What destroys a gun is getting the powder burn to escalate into an explosion. Light loads that uncover the flash hole, mixed loads where a fast powder accelerates the pressure and detonates the slow bulk powder in the load or just a weak gun. Pay attention and if you want more power, BY MORE GUN!
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