Privacy guaranteed - Your email is not shared with anyone.

Welcome to Glock Forum at

Why should YOU join our forums?

  • Reason #1
  • Reason #2
  • Reason #3

Site Description

A Brief Primer on KB's

Discussion in 'Valuable Info' started by WalterGA, Sep 6, 2004.

  1. At the range I go to, there is a display case with a couple of S&W N-frame revolvers and a bull-strong Ruger Blackhawk. All have FULLY-SUPPORTED chambers--and all experienced true kB! events--topstraps are curled upward or broken, cylinders are broken, etc. Little tags identify the cause for each: TRIPLE charge, wrong powder, and wrong bullet. Add occluded barrel (which really encompasses "wrong bullet") and you have the Usual Suspects for TRUE kB! events--excessive pressure.

    I've seen dramatic case failures when a 9mm cartridge is fired in a .40 Glock (don't ask!). Guess what? NO DAMAGE to the gun! WalterGA was right in this matter, as he so often was on other matters.
  2. mobocracy


    Apr 25, 2005
    Heh..kind of like this?


    That's a 10mm case that managed to get fired in a .45 ACP 1911. Didn't even keyhole, but it also didn't eject right or feed the next round.

    A friend of mine, military gun collector and Ph.D. managed to load a magazine of 10mm into my .45 ACP 1911 and let one off. He's suitably punished at every range session with questions as to why "this bullet won't fit...".

    It didn't damage the gun or magazine at all. After field stripping and checking the barrel for obstructions, it managed to be as accurate as ever and I've had no problems in 1k+ rounds fired through it since.

  3. RtBrane


    Aug 5, 2006
    Gentlemen, you are wandering off track when you talk about firing smaller than proper caliber rounds. While the brass may look dramatic, you do not have a pressure seal in the barrel, which is required to burst the chamber. Probably don't have a good seal at the breach face either. If the bullet was lead, you might cause some lead to be smeared in the rifleing by flame cutting as the hot gasses blow past the undersized slug. This might be a problem with later shots with proper size ammo.
  4. English


    Dec 24, 2005
    I am not denying the existence of many KBs due to overcharging and many due to the less obvious problem of sub minimal loads flashing over. These are all well know and well understood. Equally, a slightly too large bullet with a normal charge will cause a KB - this does in fact obstruct the bore, just as I am suggesting for other cases, for long enough for the pressure from a normal charge to build high enough to burst the barrel.

    When we take away the obvious cases of why KBs happen we are left with a mystery. There seem to be many cases where none of the obvious reasons apply. I am doing no more than try to address those cases.

    To answer the question directly: no I have no personal experiences with revolver KBs. Neither do I know of anyone who has such experiences in any number which would provide significant evidence.

    I know of one case in which a friend changed his mild revolver loads to a different but seemingly identical lead bullet from a very respected maker and changed propellant at the same time to a charge that should have had the same power. (There were complicated reasons for why he made two changes at the same time.) They were rather inaccurate but the first that he knew of a real problem came on only the second cylinder when the cases would not extract. He found massive leading and was obviously close to a KB. He is meticulous about cleaning and so he was sure that there was no leading before he started the session and I am sure he was right, but after a hard time getting the leading out he fired another six to see if it was a freak occurence. The result was more heavy leading and he stopped the experiment before the cases seized in the chambers. He scrapped all his ammo from that batch but opened and measured the charges and they were as they should have been.

    This is not conclusive evidence of anything other than that we are playing a game with rare random dangers.

    The position that many of us fall into is to assume that we understand these dangers and that they can't happen to us because we know better. I believe that the "knowledge" that loose Glock chambers cause KBs is one such example. No one has come up with any sensible mechanism by which a loose chamber can cause a KB. Before someone tells us again that Glock chamber walls are thinner than X chamber walls, can I repeat that they still do not burst with normal pressures and that an exceptional event is required to seize a case into a chamber or burst a barrel. Both of these categories expand the bore size before in one case it bursts and in the other it springs back to size. Other makes might offer a little more margin but the phenomenon still exists.

  5. RtBrane


    Aug 5, 2006
    Did you catch my post at the bottom of page 11? I'd like your feedback on my data.
    I haven't made it to the range yet, but I did more testing. Did some further hand cycling, with various amounts of ammo in the mag. With a full mag, I got the least bullet setback, from 0.00 to 0.001". Half-mag produced 0.001 to 0.002". No jams. Re-cycling the same round to see if the setback continued, which it does. Tried 3 brands, 4 bullet weights, plus a commercial reload. Some move easier than others. This is very limited testing, using one Glock, a G27.
    I suspect that LEO's might have more KB's, if my theory is accurate. They typically load and unload their guns each shift. Also, some have specified practice ammo, and don't normally shoot their duty ammo. If the same round gets chambered often enough, might be a problem.
    What I don't know is what pressure correlates with bullet setback in the .40sw. I imagine there are a number of variables involved here, but I don't have the background to say at what increment setback becomes critical. I seem to recall hearing that along with increased pressure, it induces a spike in the presure rise, which compounds the problem.
    BTW, I have seen a G27 after a KB. I arrived at an indoor range shortly after, and had a look at the remains. This was the first G27 the store received, I think, and they added it to the rentals. The rangemaster took it out first, and it grenadeded(sp) with the second mag. (They only allow factory ammo in their rentals.) I think the slide may have been the only salvageable part. Beat the hell out of his hand. They sent it into Glock, which sent back a new gun. The chamber was blown apart. Destroyed the frame, mag, trigger group was blown out. Glad I wasn't holding it. At the time, we assumed it was a bad barrel. Maybe, maybe not!
  6. English


    Dec 24, 2005

    I certainly found your posts interesting. My immediate thought was "If the .40 then why not the 9 since the .40 bullet is held by a bigger circumference area than the 9?" My next thought was that the pressure is limited by the tension in the case wall pressing inwards on the bullet and that as the 9 has a smaller diameter then this will produce a greater inward pressure for the same tension. Greater pressure over less distance probably equals the same total grip.

    There is no doubt that setback bullets will produce higher pressures. I doubt if a 0.001" will make much difference but by the time we get to 50 or 60 thou instead of one, that could be significant. What you say about LEO's is interseting. The problem was recognised by Fairbairn and Sykes back in Shanghai. The instituted a controlled cycling of their ammunition so that all duty rounds were shot in training within a three month period. They also had a system of preventing individual rounds being chambered too many times. I don't remember the figures of the scheme but it was all set out in tables.

    As a round is chambered it follows a random path as it bounces from surface to surface. Part of this randomness would almost certianly exist even if every round was absolutely identical (see chaos theory) but in fact there will be a variation in charge and bullet weight, a variation in case wall thickness and consequent possible tension, and a variation in crimp. As you have shown with hand cycling rounds, the speed of the slide after recoil is not the same as with hand cycling. This is because the slide bounces off its stop after recoil and so has a running start before the recoil spring starts to accelerate it towards the breach. So a slighty heavier charge could produce a faster slide pickup and if that is followed by a bad bounce for the next cartridge it could cause exceptional setback in a cartridge with a weak grip on its bullet and that could do it! It takes a lot of fairly rare things coming together but KBs are very infrequent.

    I am not trying to knock Glocks, I think that they are a brilliant design and no engineer can anticipate all possible problems, but there seems to be some evidence that this is more of a problem with Glocks than with other makes. The same goes for the .40S&W compared with other cartrridges, though all have the same problem at, perhaps, a lower frequency. One of the complaints about .40S&W Glocks, which I share, is that they were built on a barely converted 9mm platform. This was, of course why the .40S&W was invented in the first place! Many people complain about its snappy recoil and I think that is because the slide is not heavy enough. The momentum imparted to the pistol by the bullet is much the same as a .45 and the most significant thing is that the bullet has left the barrel before the breach unlocks. The felt recoil is almost entirely a matter of the way that the slide moves after the bullet has left the barrel. I believe that the snappiness of the .40 cal Glocks is because of the extra speed with which the slide hits its stop. If this is so then the speed of return of the slide will also be greater because it starts off with a bigger rebound. It all fits together reasonably well as an explanation. Congratulations!

    It might even be possible to find forensic evidence in the form of a cartridge case showing evidence of the bullet being driven back before it is fired. Apart from that it should be possible to do lots and lots of painstaking test and measurement to produce a distribution curve of the ammount of setback so that an estimate could be made of the frequency of sufficient setback to cause a KB. Fire a round. Take the chambered round out and measure it. Repace it as carefully as possible from another magazine. Replace the original magazine. Fire the previously measured round. Take out the chambered round etc. A few thousand round should be enough - of each of several manufacturers of course. I would not like to do it! In any case we can't assume a nice distribution curve or that our batch of ammo is representative.

    The phenomenon that your hypothesis does not seem to explain is how some KBs combine with a partial breach opening. (I repeat that simply firing out of battery will not produce excess pressures and cannot seize the case in the chamber but would just blow the case without damage to the barrel.) Somehow the pistol has to be in battery before it is fired and then excess pressure still has to exist as the pistol comes out of battery.

    Maybe I will think about this another day.

  7. A very interesting analysis of the Glock KB issue was done by Mark Passamaneck, a forensic engineer who investigates "accidents and failures for a living." His work is available in two places (that I know of); an article on the GlockFAQ website and a chapter in the excellent second edition of Robin Taylor's book, The Glock in Competition.

    He blew up his Glock unintentionally, blew some up intentionally under laboratory conditions and examined others which had blown up.

    Like WalterGA, Passamaneck makes a clear distinction between case failures and barrel failures. On the subject of "unsupported" chambers, he writes:

    "The loose, partially unsupported chamber has attracted a lot of the gun store commando spotlights in the past few years, but the chamber dimensions, in and of themselves, will not cause a KB. Additionally, case failures exhibit a very different failure mode than gross overpressure....Case failures rarely damage the slide or barrel. Sometimes magazines, triggers and mag releases are liberated, but usually a few bucks in parts puts them back together again. The pressure vents downward through the front part of the grip...."

    In contrast, "[t]he damage and potential injury due to a barrel failure is quite different. Barrel failures are caused by gross overpressure. Obstructed barrels, double charges, deep-seated bullets and severe leading can be responsible for gross overpressurization."

    He continues "Of the several dozen blown Glock barrels I have personally been involved with reviewed injury reports from, the worst injury besides soiled shorts and bruised confidences are blood blisters and a sprained finger here and there....[t]here was not one slide separation and not one grenaded chamber. I cannot say that for other blown guns I have examined. A blown Beretta or a blown 1911 can severely injure the shooter. The chambers on most other pistols are round on the exterior, so there is not a predictable failure location....Good engineering design incorporates predictable failure locations and modes. Glocks are very strong indeed. If I was forced to fire a double-charged or otherwise excess pressure round, I would choose a Glock to shoot it in every time."

    Passamaneck has much more to say on the topic of this thread and I commend his chapter in the Robin Taylor book to your attention.

    Bottom line: the generous chamber dimensions of Glocks, particularly in larger calibers, may make them more prone to case failures but DO NOT make them more prone to blowing up barrels!
  8. English


    Dec 24, 2005
    Thank you gary. I keep recommending "The Glock in Competition", especially relative to leading dangers in polygonally rifled barrels.

  9. mpmarty


    Aug 11, 2006
    Well, I guess I'll chime in here with a personal experience.
    My shooting partner used to compete in IPSC back in the late eighties with a S&W 4516. This is a 3" barrel 45acp. In order to make "major" we had to load his ammo with a 265 grain keith type cast wad cutter and max charge. He got smart and sold the smith and bought a Glock 17 and I was left with a bunch of 265gr. 45 auto ammo. Well, I had my Glock 21 and decided to just use it as a noisy bullet puller.

    One night at the indoor range, I had a guy on each side of me shooting 357 revolvers with short barrels. The 265gr ammo would sometimes not feed and the slide would close on an empty chamber. Sure enough, I had a ftf and assumed the empty chamber situation and without thinking (and stupidly) jacked the slide and fired again. What had happened was the first failure was a round without powder which moved the slug down the barrel about an inch. The second round went off and I got one hell of a kick and two slugs hit the target downrange the prinmer was completely flattened on the fired case, there was a small smiley face at six o'clock and I had a very slight ring bulge in the barrel. That was it, I continued to use that barrel in that gun for another match and then sent it in to Smyrna for a new barrel. As I recall the load we were using was 5.5 grains of red dot. If ever an overload/overpressure was going to cause a KB that was a great opportunity. As it happened, no real harm or damage and I gained a great deal of respect for my 21.

    Marty in Oregon
  10. bigK


    Jul 20, 2006
    I was in a gun shop yesterday and they have a G23 with a kkm barrel on display that is split in half....very impressive what guys can do with their reloaded .40 ammo...:animlol:
  11. thogue


    Sep 23, 2007
    I think this should be noted and consider as an important part of this read. I have yet to read this guys research or "confirm" it but it makes total since in my eyes (I got an A is physics). I have been really worried about reloads/Kb! issues/case failures.

    one thing I have determined = KB DOES NOT MEAN ANYTHING. ITS SHORT FOR KABOOM WHICH YOU SEE IN CARTOONS. It is a total failure to describe real problems with guns. Someone who obviously did not fully understand and evaluate problems(edit: major hince on problemS plural as in more than 1).

    and Glock owners should no have fears. Just practice safe shooting and everything is ok.

    This post was extremely helpful to me and I think a full read took me over a half hour.

    another late edit: Sorry about my angst about "Kb" but I really feel like it only adds confusion. As someone who just became seriously interested in glocks I found this almost offensive. I did lots of research of reloads and this supposid kaboom. Forum searching before I figured out it was "Kb" I did not get much info.... anyways... why add such confusion? why cant we just say fire o-o-b, case failure, barrel failure, etc...?
  12. rmgunsmith


    Nov 22, 2007
    I recently experienced my Glock 20 KB after sucessfully firing four full magazines of both factory PMC loads and custom loads from my shop. When it happened the magazine shot straight out, the Wolff recoil spriing and one pice guide rod launched 20 feet, along with some of the polymer frame. The fram was cracked almost in half and the new Storm Lake barrel was split the entire length on the underside. The barrel tried to blow as the front of the slide was bowed.

    My hand felt this sharp pain, especially in my trigger finger, which turned black, and hurt like heck. My right hand went numb briefly, but after two weeks there appears to be no physical lasting damage.

    I have sent the Glock 20 back to Davidsons who is forwarding on to Glock. My sales rep at Davidsons said he had never seen anything like it and wondered how I kept from being injured.

    I talked with a Glock representative at the 2008 Shot Show, who sounded positive that Glock would probably replace it.

    I see from your post that they did even with an aftermarket barrel. Thanks for the encouragment.

  13. Arc Angel

    Arc Angel Deus Vult!

    Sep 20, 2003
    Penn's Woods
    :freak: Not that anybody cares; but, according to the guy who invented the term, it ain't, 'KB'; and it ain't, 'KB!'. Instead it's, 'kB!' or, 'kaBoom!'

    I've done a pretty good job of intentionally avoiding this thread for the past 3 years. I will now, however, venture an opinion: I think that English's thinking is closer to what's actually going on than anything else I read. IMO, there is more to the picture, though, than currently meets the eye!

    I, also, think that the newly discovered phenomenon of, 'Glock frame harmonics' is involved: e.g.; The Haddon Heights, NJ; and Albuquerque, NM 40 caliber Glock problems along with the subsequent changes that Glock made to the frames of recently manufactured 40 caliber pistols.

    Personally, I think that Austrian Engineer's comments on G-22 performance AND frame harmonics go a long way toward understanding exactly, 'What' is happening. I, also, find English's other comment on, 'primer smears' to be interesting.

    As I type this I'm wondering what happens when a barrel firing a high speed AND high pressure bullet begins to tilt at the exact instant that primer ignition takes place? Of course, I don't know anymore than anyone else on this board. I'm just speculating by offering an additional hypothesis for further consideration. So far, nobody has offered a demonstrable or definitive explanation for Glock 40 caliber, 'kaBooms!'; and, believe me, neither am I.

    Just thinking out loud, that's all. :)
  14. shotgunred

    shotgunred local trouble maker

    Mar 1, 2008
    Washington (the state)
    I have had two events with my glock 23. Both of them involving aa#5.
    I bough my 23 when they first came out. I preordered it before they were available. At the time AA#5 was the recommended powder for reloading. I now have two cases of the stuff on a shelf. It may have its uses but I wouldn’t use it for my glock ever again.

    First time damaged the barrel. I found a small crack on were the chamber meets the barrel.
    Second time the side of the bullet case (unsupported spot) blew out and took the ejector with it.
    I don’t believe that either time was the guns fault. I think it is an issue of AA#5 burning too fast with 180 grains of lead and the pressures that causes.
  15. TexanGlockFanatic


    Dec 3, 2008
    Howdy everyone. I am new to this forum but I have read some of this thread. I had a KB a week ago. I purchased my third Glock on Nov. 21 (2 - 9mm and now a 45). It is a Glock 36. I had fired about 70 - 80 rounds of Winchester target ammo. I then loaded 5 rounds of some self defense ammo that I have (I use the same brand in my Glock 26 and have fired at least 50 - 60 of this brand in the Glock 26 before) in my Glock 36 and let the slide ram home. It was fully in battery. The first round I fired blew out at the bottom of the case, the magazine, broke the trigger, and the magazine release, and made the polymer frame swell.

    I have called the ammo company - RBCD in San Antonio, Texas and they had me ship the gun and some of the ammo to them. The day they received it, they called me and said they would not repair my gun as the ammo is to be used only in fully supported chambers. The ammo company's website said this: "RBCD Performance Plus - Handgun /Rifle Ammunition has the highest velocity of any commercially available ammunition, at Standard Pressure Levels (never Plus P or higher pressure levels)." It also says this: "The Ammunition loaded by RBCD Performance Plus, Inc. is manufactured with new cartridge cases, powders and primers designed to SAAMI and our strict and exacting specifications. Always at Standard Pressure Levels (never Plus P or higher pressure levels)."

    So they shipped the gun back to me b/c they would not fix it and I argued with them on the phone and there was nothing they were going to do. Here are pictures of the gun and case that blew out the side.


    Broke magazine release and trigger

    Frame buldging

    Crack in frame on both sides of gun around the mag. release

    So the gun is off to Glock but they say they won't pay for repairs as it is an ammo issue. :-(

  16. bluejdixon

    bluejdixon Ammo Hoarder

    could you have possibly posted smaller photos?
  17. TexanGlockFanatic


    Dec 3, 2008

    They are just links off my website. They are much smaller here than on the website so maybe it is something with Glocktalk. However, you can check it out at and see bigger pics.
  18. bluejdixon

    bluejdixon Ammo Hoarder

    Holy crap! So glad you got to keep your digits.... wow!
  19. TexanGlockFanatic


    Dec 3, 2008

    I was very blessed that I only had a couple of blisters and sore palms!

    The ammo company will not fix it through some legal jargon and so it is at Glock. They have said they will not fix it under warranty as it was an ammo issue, but I have sent a letter asking them to put pressure on the ammo company with me so we will see what they say.