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A Brief Primer on KB's

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

  1. fabricator

    fabricator Got Biodiesel?

    Aug 28, 2003
    Grand Haven, MI
    Much better;)

  2. since you received no real answers from the last time I checked in I'll try.
    KB stands for KaBoom. Its when the unsupported lower section of the case(because of the barel/chamber design) lets go and a rupture occurs at the moment of firing. The "hot gas" is directed downward through the magwell, and some out through the barrel with the bullet if your lucky and with the extractor.

    Its generally an issue with .40 caliber Glocks and bad cases.
    Use only new .40 factory amo and you'll be fine. If you reload be very careful on overcharging.

    Its not a common enough occurrance to worry about imo.

  3. fabricator

    fabricator Got Biodiesel?

    Aug 28, 2003
    Grand Haven, MI
    Especially if you shoot a itty bitty .40 bullet.
  4. I'd suggest reading the beginning of this thread. A case failure cannot usefully be considered a kB! A REAL kB! occurs when significant overpressure cause the GUN to blow up, bending and ripping steel. ANY gun will blow up if subjected to pressure beyond its designed tolerance. Overpressure events usually occur when one (or more) of the following is true: (1) the round is over/double charged or charged with the wrong powder. (2) the bullet is set back in the case, reducing volume and increasing pressure, (3) a round is fired through an obstructed bore, possibly a bullet left by a previous under-charged round (a squib). Overpressure has essentially nothing to do with "unsupported" chambers.
  5. jmacelree


    Jan 6, 2005
    Gary is right to advise you to start at the beginning of this thread.

    Some will present a technical definition, but in general terms, KB means - KA BOOOOM - Blowing up the gun - Blowing apart the gun - Very bad if you are close to the gun - Injury or death can occur. There are many many reasons for a KB.

    There are also many many reasons for over pressure. I would add to the above that over pressure can also be caused by the over all length (OAL) being too long which engages the bullet with the lands and groves of the rifling before the detonation of the round. Loading the wrong (too big) diameter bullet can also cause over pressure. Very fast powder in a big case and too much air or space combined with a heavy bullet might cause over pressure.

    Rounds that do not fully load into the chamber and the gun (defective perhaps)still allows the round to be detonated causing an explosion. This may not technically be over pressure and it may not technicly be a KB (depending on who supplies the definiition), but there is an explosion and the explosion is not contained because the case is not supported. The case is ruptured and may cause collateral damage. If you are the one holding the gun at the time, you will hear KA BOOOM and you will be lucky if no one is injured.

    If you are reloading, you need to follow the recipe. You need to be very careful and remember you are dealing with a controlled explosion in your hand that is not far from your head. The "Myth Busters" on the Discovery Channel did a show on plugged shotgun barrels with interesting results.

    Some people have bad luck and report a KB even when they act cautiously with a modern gun and new factory ammo. KBs have been reported with many brands and types of guns and ammo. Some may be more susceptible than others.

    If you are using factory rounds you need to make sure your gun is in good working condition and designed for those rounds (some rounds are marked as high pressure or high velocity). Some guns, depending on age, condition, materials, design and etc, etc should only be fired with lower pressure rounds. Some are not safe to fire at all. Guns are mechanical devices and like all mechanical devices need to be properly inspected and maintained but all will eventually fail.

    Some KBs have been reported with "old" factory rounds. Yet many people shoot "old" military surplus regularly without problems. Others report KBs with rounds that were found in an old drawer or box. A cutious person would not eat a pill he found lying around because he does not know what is in it. The same should apply to ammo.

    Some people like to test the extremes (like the guy who fired an elephant rifle round in a modified handgun ;g - reportedly lost part of his hand and it my not have been a KB). Others do not use common sense and caution;P. Some in both groups have been seriously injured or killed.

  6. English


    Dec 24, 2005
    This is clearly a very popular thread and I have amazed myself by reading it all. Rather than go back and find all the references I will just refer to the ideas.

    One of the most striking things is the aggressive interaction initiated by the man (avatar of Tasmanian wolf) who has had twenty Glocks but thinks that they are more likely to blow up because they have sloppy chambers. His extremely aggressive initial approach triggered everyone else into a fight mode rather than a rational problem solving mode. He has done the thread a great disservice. His principal belief that loose chambers cause blowouts has to be nonsense. All cartridge cases expand to seal the chamber, more or less, regardless of how sloppy the chamber is and then spring back most of the way. A sloppy chamber will produce a bigger diameter “empty” than a tight chamber. The expansion happens in the early phase of the ignition because the brass is very weak in comparison to the chamber. Any “slap” of brass on chamber at this stage must be negligible compared to the later rise in pressure. If anything a sloppy chamber will reduce the total pressure because it provides a bigger space for the “burn”.

    All barrels must be designed to some compromise with respect to their resistance to exceptional events and all will blow up given the wrong, or right, circumstances. I doubt that the G21 is more likely to blow up than the G20 because, as asserted by the same man, their exterior diameters are the same but the hole in the 45 is bigger than the hole in the 10mm. The standard pressures are nearly twice as high in the 10mm and so the 45 has less likelihood of a charge big enough in the right circumstances. When we come to the .40S&W in comparison to the 9mm he might have a valid point. The working pressures are much the same but the chamber wall is thinner in the 40. I don’t believe it but I could be convinced by appropriate evidence.

    I have long believed that all manufacturers made a serious mistake by treating the 40 as a bigger bore 9mm just because it could be fitted into the same frame. It shoots bigger bullets at the same velocities and so has more recoil. It needs a correspondingly heavier slide and barrel to slow the slide recoil velocity. It is significant that the accuracy of the .40S&W from a revolver is inherently high but from an auto it is poor compared to other autos. I believe excessive initial slide velocity is the cause and initial slide velocity is hardly affected by spring strength. I think Glock should go the same way as with the GAP45 and increase the slide weight but I don’t think that this has any connection with KB incidents.

    Why do we care whether the chamber is tight or loose? For best accuracy we want a tight chamber and a tight slide but a relatively small amount of dirt or grit can cause a failure to feed or failure to go completely into battery. This is not just because there is more friction in the chamber. The timing of the rise of the cartridge depends on both the strength of the magazine spring and the speed of the forward motion of the slide. If the slide is slowed by dirt the magazine spring will give the cartridge too much vertical velocity relative to its horizontal velocity. The result will be that it is too high by the time it reaches the chamber mouth and can jam against the upper edge of the chamber. A slightly looser chamber is not so sensitive to this timing problem and will also put up with a more angled presentation of the cartridge. If you want a reliable defensive handgun that keeps going bang when you pull the trigger until the magazine is empty you need a slightly sloppy slide that does not get slowed down by dirt and a slightly sloppy chamber. If you want maximum accuracy then you want both to be tight. There is no “best” solution – it’s a compromise. In this case, versatile as they are, the Glock pistols are strictly designed for combat use which has to include difficult conditions. They don’t need to shoot into 1 or 2” at 25 yds because 4” is good enough for the purpose. If you want to reload, get better accuracy or shoot lead bullets then you need an after market barrel made for that purpose. If you want service reliability and acceptable accuracy for the purpose with a little more velocity for a given pressure then you want a Glock polygonal barrel and the bulged cases don’t matter.

    There is no indication that the so called unsupported barrel causes any other problems (if you don’t reload) because the case wall at that point is thick enough not to burst in a normal firing event. If you block the barrel with a squib load and then fire another normal cartridge you just might be lucky enough for this section to blow out while the barrel is still locked to the slide and this might just save you from a far worse barrel burst. Was it designed as a safety valve? I doubt it! It was designed to give a shallower ramp into the chamber which in turn improves reliability. Could the barrel have been located a little further forward at the cost of miniscule extra length of the pistol? Probably! Would it have been better if it had? Possibly. Was it therefore a design fix in late development? Could be. Does it matter in the least for a combat pistol? Not a jot!

    The man who did the entirely sensible experiment of successively shortening a 10mm case to find out whether his .40S&W Glock would fire out of battery had it right but I don’t think that is part of the KB problem. If the cartridge is far enough out of the chamber to be dangerous the striker will be blocked in all but very rare cases. In this category of rare events the cartridge would be ignited before it is properly supported and the result would be a burst cartridge case not a burst barrel because the case would burst long before the pressure reached a level which would endanger the barrel. There has been no evidence put forward of any such mechanical failure of the striker safety block being the source of a case blow out.

    The head of the Portland Police Bureau should have been sacked over the G21 KBs. Perhaps he has been by now. To have two failures within two days when the last was five or so years previously has to be an ammunition problem. It was all the same batch of ammunition and not their normal ammunition but the guns had been working for a long time before that training day with no problem. Coincidences do happen but you shouldn’t rely on them. The fact that one failure was at the end of the day and the other was only 20rds after cleaning also says that it was not a build up of dirt in the conventional sense. Those who start with preconceptions are likely to make costly mistakes. To carry on shooting after the first KB without determining the cause seems close to criminal negligence. To try to put the blame onto Glock seems to be either a case of passing the buck or culpable stupidity.

    I like the original theme of the thread which distinguishes between a barrel splitting incident and a much less dangerous burst case incident but I will shortly explain why I think that many of these incidents have the same cause.

    The barrel and slide start moving back together as soon as the bullet starts moving forwards. Under normal circumstances the barrel does not cam down out of breech lockup until the bullet has cleared the barrel and the gas pressure is virtually zero. This obviously happens very rapidly and the empty cases of my G20 10mm show a smear of the firing pin indentation on the primer so the barrel is camming down before the striker has rebounded.

    How can a barrel blow up? The simple but unhelpful answer is because the pressure is higher than it was designed for or it has been weakened in some way irrelevant to this discussion. So the proper question is how does the pressure get so high that a barrel can blow up? This takes many times the working pressure! There are two ways. One is that the cartridge has been over charged for the propellant used. The other is that it is burning in too confined a space. I think that the first is rare in auto pistols because they use small cartridges designed for smokeless powders and so do not have much room for a double charge, which is the most likely reloading error. This is much more likely with what are actually old fashioned revolver cartridges designed originally for black powder and which therefore have more spare volume.

    The simplest form of “too small a space” is caused by a load with no propellant, or very little, which leaves a bullet part way up the barrel. The next bullet then comes to an abrupt stop but the powder keeps burning even faster than normal because it is hotter, and the result is an explosion. Bear with me for re-stating the obvious – for those new to such topics it is necessary and I am getting to the denoument as fast as I can. Likewise if you load a very heavy bullet with a powder and charge designed and tested for a light bullet, the space available expands too slowly, the pressure builds too rapidly and damage is likely to follow. Even if you crimp the bullet too tightly in the case the extra time it takes to start moving can be enough to cause a dangerous build up of pressure as the powder has extra time to “burn” before the space available to it has opened up enough to both cool its temperature, and therefore rate of reaction, or to reduce its pressure by containing it in a bigger volume.

    How else can we achieve this undesirable effect? If a previous bullet or bullets leaves a substantial deposit part way down the barrel, then the next bullet will slow down enough for pressure to become high enough to cause damage. The actual damage will depend on how much it is slowed and how far down the barrel the obstruction is located but in any case the bullet can end up leaving the barrel and taking the obstruction with it. The PPB should have looked for it! Remember that the barrel and slide have started to recoil together and that the engineer who designed and tested it expects the bullet to have left the barrel before the breech unlocks. But is this case the bullet has been slowed down even though the pressures are much higher than he expected and his calculations and testing are worthless.

    If the partial obstruction is a short way down the barrel the recoil will have been reduced at an early stage and the slide velocity will be low. The breech will still be locked as the pressure builds to a dangerous level and the barrel will bulge or burst.

    If the obstruction is further down the barrel the pressure will be lower because there is more space and so a burst barrel is less likely but a more important effect will have taken over. The bullet has moved further and faster before meeting the obstruction and so will have produced more recoil. This will have produced more slide velocity which will have unlocked the breech. The high gas pressure will be forcing the cartridge case walls against the side of the chamber very hard so the probable result is that the head of the case blows off taking the extractor with it but leaving the rest of the cartridge expanded tight in place against the chamber. This is because the chamber has actually been swelled outwards by the excessive pressure but has than sprung back to grip the walls of the case when the pressure fell. This fits the picture of the barrel shown earlier in the thread.

    This hypothesis fits the facts and provides a single explanation for many of both types of explosive event. The problem is an ammunition problem and is nothing to do with the weakness of the barrel or the unsupported section. As to what manufacturing fault of the bullet can leave such an obstruction, I cannot guess. Perhaps it needs a rare sequence of failures.

    I believe that case blowouts are much more likely to be caused in this way than by a failure to go into battery combined with a failure of the striker safety block. If I were a proper engineer I suspect that I could do calculations based on the pressure resistance of the exposed case and the limitations on bullet velocity that would be created to show that this was so.

    The moral of the story is that we should use good bullets. The difficulty with this is that, for all we know, some apparently good and expensive bullets might be at risk of this occasional failure. What we need is a data base of KB events, including case blow outs, so that we can see if there is any consistent pattern to implicate particular bullets or firearms.

  7. emm


    Sep 13, 2004
    English - I've wanted to see a database for a long time, that way we all could get a good analysis of what the problems might be.

    I just returned a "probably" perfectly good barrel because I can't "afford" to blow up a G29 that wouldn't be covered by Glock Inc. The main reason for being "scared" is I just can't get that good KB data analysis that I need...

    Possible fields:
    Gun Model
    Barrel Length
    Barrel Manufacture
    Un-Supported Area Measurement
    Ammo Manufacturer
    Lot Number
    Bullet Wt
    Bullet Manufacturer
    Bullet Type
    If Reloads
    Power Type
    Power Wt
    Time of Occurrence
    Who was shooting gun when it occurred
    Weather Conditions
    KB Info
    What Broke (barrel, frame, slide etc...)
    and more...
  8. MOHAA Player

    MOHAA Player Guest

    I owned numerious Glocks over the years in all calibers and fired alot of different rounds and never had a problem with the stock barrels.
  9. Robert302


    Oct 22, 2005
    Columbus, Texas
    I think "emm" must be a paranoid crack smoker..

    The chances of having a KB are very slim to none with a glock.

    Go buy a Hi-point or some other gun, etc. When it jams at the moment your life is being threatened, you will wish you kept the glock.

    To Hi-point owners: no hate to Hi-point guns, I have the 995 9mm carbine, it jams a few times everytime I'm at the range. I love the carbine, it is fun but I just wouldn't fully trust my life to it.
  10. AWGD8

    AWGD8 Sr. Glocker29SF

    Mar 19, 2006
    I`m not too worried about Glock KB! What the heck is wrong with you guys? :soap:

    Anyone here know an insurance policy that specifically for the right hand coverage? :supergrin:
  11. win231


    Mar 27, 2006
    I'd have to acknowledge that with most P.D.'s using Glocks (I read something like 80%), if there was an inherent design flaw contributing to KB's, there would have to be an epidemic of problems & there are not. It's possible that with so many Glocks out there, there may be more problems with Glocks, but I think it's due to improper handloads.
  12. mobocracy


    Apr 25, 2005
    Blaming improper handloads doesn't adequately explain many reported KBs, since a lot seem to have happened with factory ammo (based on what I've read).

    I think it's more likely that the unsupported area on Glock barrels just pushes the tolerance factor close enough to the edge that the large number of Glocks simply exposes it.
  13. jbremount


    Apr 17, 2005
    English....This is a picture of my Storm Lake aftermarket barrel(left) next to my Glock 23 stock barrel(right). The Storm Lake never buldges the cases even with the A-- Kicking Double Tab ammo. The Glock barrel buldges the case with winchester white box target loads. I have seen pictures of other aftermarket barrels that have even "more" case support than the storm lake barrels. Everyone is coming to their own conclusions,right or/and wrong about the glock buldge and case rupture at the 6 o'clock position. My opinion is that the the Kb problems starts with the lack of case support in the 6 o'clock area. The big time barrels makers have decided a course of action to take and are engineering and manufacturing their glock barrels with much better case support and tighter chambers than the glock factory barrels. I do not know of even one aftermarket barrel maker that is making a barrel with the same or less case support and oversized chamber as the glock factory barrel. Glocks are used by civilians and PD in the U.S. I think the big oversized chamber and lack of case support is more of a problem for them. I personally would rather have standard rifing and the ability to shoot lead in a barrel myself. Quite a few people reload in the U.S. To sum this all up, I agree with the barrel makers, get a barrel with a tighter chamber and "maxium case support" for the high pressure .40/10mm caliber guns. I believe Lone Wolf dist. is coming out with a barrel for the .40 that will probably be the best deal for the bucks.

  14. RtBrane


    Aug 5, 2006
    Normally, I load my G27 (40sw) by chambering a round from a fully loaded mag, then struggle to top off the mag. Wait a minuite, I've got an empty mag, I'll put a single round in that for loading the chamber. Yeah, right. Jammed against the barrel ramp. Start over, same problem. Tried slingshot and slide release, same result. Not everytime, but better than 50% jammed. (Through several classes, this gun has never malfunctioned.) Tried several different brands, hollowpoint and flatpoint. All will jam. Smacking the bottom of the mag will cause the round to finish chambering.
    After this, I noticed the rounds didn't look right. Compared them to fresh ammo, realized all had some setback.
    Hmmm, time to bring out the calipers and run a small test.
    Jammed produced setback from 0.015" to 0.065":shocked:
    Non-jam loading also produced setback, as much as 0.019"
    However, I also measured bullets moving out after chambering. 0.001 to .004" Appearently, the slide velocity is rather high.

    Obviously, the chambering dynamics are different between hand cycling and firing, since I've run mags dry many times without any jamming on the last round.
    However, the bullet displacement that this little test indicates, brings me to the tentative conclusion that this may be the causitive factor in some of the case ruptures, and chamber failures (KBooms). Especially the puzzling factory ammo KB's.
    It may also explain the accuracy complaints about the .40sw, since varying the powder space in the case will effect pressure which changes bullet placement at the target.

    BTW, for those interested, the minimum chamber wall thickness I found was 0.080" (RH side). I measured the chamber walls of a Colt Pocket9 (only 9mm on hand), minimum was 0.074"

    I think I'll take calipers with me next time I shoot, and check rounds that have been dynamically loaded.

  15. BrokenArrow

    BrokenArrow Millennium Member

    Aug 11, 1999
    Lost In Space
    How's the reliability w the aftermarket Glock bbls w more case support?

    Only experience I have is w Jarvis Glock bbls, and they caution while more supported, may not be as reliable. :alien:
  16. mobocracy


    Apr 25, 2005
    A drop-in replacement barrel might give feed problems for two reasons. Most have tighter chamber tolerances, which means that out of spec ammo may not chamber or eject reliably. And then there's the question of barrel fit in a "drop-in" replacement. Mine's worked well, but it's not hard to imagine that a replacement barrel maker might err on the "tight fit" side, impacting performance.

    I'd personally like to see aftermarket barrels come in "combat" chambering/fits, with slightly looser tolerances and "match" chambering/fits.

    I had to tighten my 10mm crimps .003-5" at the case mouth to get my reloads to run reliably in my Glock 29 with a KKM barrel. Previously they worked great in S&W 1006 & 1066, but were .003-5 larger than Remington UMC factory loads.
  17. English


    Dec 24, 2005
    There is a lot of feeling but no evidence that the relatively loose chamber and unsupported area of the Glock chamber are significant contributory factors in KBs. Both will weaken the brass for reloading but lots of KBs have occured with factory ammo. Lots of KBs have also occured with many different makes of handgun and in both revolvers (fully supported chambers) and in autos. The Glock chamber looks like an attractive red herring!

  18. mobocracy


    Apr 25, 2005

    Please do detail your experience with revolver KBs not directly attributable to overcharges. I've seen KB'd revolvers, but they were always associated with double charges of fast powders.
  19. BuckyP

    BuckyP Lifetime Member

    Feb 1, 2005
    You mention an out of battery condition and claim that the little extra bit of exposed case shouldn't be enough to cause a blow out. However, you must also consider the fact that in this condition the gun is unlocked or partially unlocked, and therefore is likely to be completely unlocked before such time that the pressures have dropped to a safe level.

    "the barrel is camming down before the striker has rebounded"

    I don't believe the striker of a GLOCK rebounds as it does in most autos and remains forward until partially cocked by the action.
  20. English


    Dec 24, 2005
    If I remember correctly, you have missed a large and important part between the second and third parragraphs of mine that you quote.

    Last part first - I think you are right about the striker smear. Thank you.

    If, as you are suggesting in your first paragraph, the gun can be fired while slightly out of battery then it might well be that it could come far enough out of battery for the pressure to burst the case before the bullet leaves the barrel. If this was so we would see a smiley further forward on the remains of the case and a hole in the case at the rear six O'clock position. I am not denying this but have seen no evidence of it. In Walter G's terminology this would not be a KB since there is no overpressure and burst chamber, ringed barrel and so on.

    It makes more sense to me to think of the whole range of proper KBs as variations on the same theme. They all show signs of excess pressure and not all can be put down to overcharging or undercharging. In some cases we have the remains of the case seized into the barrel so tightly that it can only be hammered out. The head of the case seems invariably to be blown into the distance. The front of the case can be seized in the barrel by only one mechanism. The pressure has to not only expand the case to fit the chamber but to expand the chamber itself to such an extent that when the pressure is released the chamber shrinks back onto the case, which had expanded to the swollen size of the chamber. It forms a compression fit which is used in some advanced mechanical assembly processes with high pressure hydraulics. In this case the pressure is not quite enough to burrst the chamber but is far higher than normal.

    Since many KBs have not involved reloads it seems that the most likely mechanism is a partial and temporary blockage in the barrel. This delays the bullet long enough for the pressure to build to very high levels. That increases the temperature. That accelerates the burn rate of the propellant. That puts up the pressure, and so on to KB. If the bullet did not move there would be no recoil to open the slide and the chamber would burst. If there is a little movement the slide will start to move but the barrel will burst before it opens the breach. With more bullet movement there is likely to be enough recoil to open the slide before the bullet leaves the barrel and we get a simple burst case or a burst case seized into the chamber.

    Since we don't find the delayed bullet in the barrel it does not form a complete blockage but since the pressures are enough to expand the bore, the bullet would be blown out past the obstruction anyway.