The Glock kB! FAQ

version 1.04, 14 March 98
Dean Speir (
Jay L. Swan (
Todd Louis Green (
with significant contributions from
Walt Rauch (

[the views expressed herein do not necessarily reflect those of .40something or The Glock Papers]


Micro Mano's Rotating GlockThe Glock kB! FAQ

  1. What is a kB!?

  2. What causes a kB!?

  3. Which Glock models are affected?

  4. Why does a kB! occur in these Glock models?

  5. Do kB!s occur in other guns or just Glocks?

  6. What is the relationship between reloads and kB!s?

  7. What can I do to prevent a kB!?

  8. If I insist on reloading for my 20-something Glock anyway, what can I do to minimize the chance of a kB!?

1. What is a kB!? Coined by firearms journalist Dean Speir, "kB!" is shorthand for kaBOOM!, which is the written representation of what happens when one has a catastrophic explosive event in one's firearm, or, for the purposes of this FAQ, one's Glock.

2. What causes a kB!? Catastrophic failures may be caused by a variety of problems, but in general a Glock kB! is as a result of a case failure.

The case failure occurs when pressure inside the cartridge increases to the point that it cannot be contained by the case and the material of the case fails, allowing hot gases to escape from the ruptured case web at damagingly high velocities.

The resulting uncontained forces can blow the magazine out of the gun, emulsify the locking block, cause the tip of the trigger to be snipped off, ruin the trigger bar, rupture the barrel, peel the forward edge of the slide at the ejection port up, and do other nasty things. In general, Glocks tend to contain case failures fairly well, but under some circumstances they can cause injury as well as damage to one's gun. At least one LEO has been injured in a kB! involving a Glock 21 and a Winchester factory overcharge.

Additionally, there is some evidence of there being another cause of a kB!... a barrel failure caused by improper metallurgy.

3. Which Glock models are affected? Speir has documented many instances of kB!s, all of them in the Models 20-something Glock (.40 S&W, 10mm and .45 ACP). Speir has no confirmed cases of Glock kB!s in the 9 x 19mm (Models 17, 17L, 18, 19 and 26) or the .380 ACP/9 X 17mm (Models 25 and 28).

4. Why does a kB! occur in these Glock models? Reports compiled by Speir from various independent laboratories are inconclusive as to one single cause for the catastrophic failures.

There do, however, appear to be several contributing factors which collectively may induce catastrophic case failures:

Firing out of battery. Most Glocks will do this to some degree, especially those improperly maintained.  [editor's note: most semiautomatic handguns of any manufacture may fire out of battery; whether Glocks have a proclivity for this is open to debate]
Significantly overpressure rounds. These occur mostly in homemade reloads or in commercially remanufactured ammunition, but have occurred in factory ammunition as well.
The lack of full case support in the critical area over the feed ramp of all large caliber (.40 S&W, 10mm, .45 ACP) Glock pistols.

(Ostensibly as a measure to promote feed reliability, Glock chamber mouths are slightly oversized. One can test this by removing the barrel from the Glock, dropping a factory round into the chamber, and observing that there is brass exposed at the six o'clock position. Take a fired case and note that there is a slight engraving if not actual bulge around the case web, which is most pronounced in the area of the case which, upon
firing, was in the six-o'clock position.)

The use of personally reloaded or commercially remanufactured ammunition utilizing cartridge cases of indeterminable generation. Unlike many rifle handloaders, many of those who reload for handguns do not as a habit separate their fired cases by generation, and each time a case is re-sized and reloaded, the brass "works" and weakens. kB!s have been documented with factory ammunition, but most of them occur with either commercial or homemade reloads.

5. Do kB!s occur in other guns or just Glocks? kB!s do, of course, occur in other guns, but no one appears to be keeping accurate statistics for most of them. Many 1911-style handguns have partially unsupported case mouths, and numerous case separations have occurred in these guns. Early .38 Super barrels were particularly susceptible. Gunwriter Frank James has documented a number of kB!s in HK USP .40 pistols, which do have fully supported chambers.

6. What is the relationship between reloads and kB!s Most kB!s occur with commercially remanufactured or personally reloaded ammunition.

Successive re-sizing and firing of a case result in eventual weakening of the brass, increasing the probability of case failure. The partially unsupported chamber in the Glock exacerbates this problem.

"Hard crimping" or overseating of bullets, particularly in the .40 S&W, can cause dramatic increases in pressure almost to the same degree as a propellant overcharge. [See Annotation #3] Either alone or in combination with a weakened case, these factors can result in a kB!

Some people have also postulated a relationship between the use of cast lead bullets and kB!, arguing that buildup of lead in the chamber can lead to pressure buildups as well. The jury seems to be out on this one as a direct causation, but lead build-up will sometimes cause a round to not fully chamber, and as Glocks can discharge with the action not completely locked up ("out of battery"), this can lead to a catastrophic failure.

7. What can I do to prevent a kB!?
  1. Shoot only new factory ammunition out of your Glock. This is what Glock, Inc. recommends, as do several members of Glock-L. Shooting reloads voids your factory warranty.
  2. Install a barrel with a fully supported chamber. Custom barrel makers include:
    Jarvis Precision
    Bar-Sto (
    Wilson (
    Briley (
    For related data, see annotation #3 at the end of this FAQ.
  3. Avoid wherever possible .40 S&W ammunition manufactured by Federal Cartridge Company prior to November 1995. [See Annotation #2]

At an October 1996 G.S.S.F. match, one competitor with a Model 22 had simply switched to a .40 S&W Sigma barrel which he averred not only better allowed him to shoot lead because of the conventional rifling, but that the fully supported Sigma chamber significantly decreased the opportunities for a kB!  Note: This procedure is neither recommended nor authorized.

8. If I insist on reloading for my 20-something Glock anyway, what can I do to minimize the chance of a kB!?
Install a custom barrel. See 7B.
Keep careful track of your brass. Load "Major Power Factor" loads only in new brass. Don't use range pickups. Don't shoot "hot loads" from used brass. Discard used brass sooner than you would normally.
Use calipers or case gauges to keep your reloads within spec. Check for excessive bulging in the case web and make sure your bullets are seated to the correct length. Also check for excessive case thinning or bulging.
The propellant AA#5 has been identified in a disproportionate number of kB!s, not only in Glocks but USP40s with barrels which do provide full case support. A number of Glock-L members have reported kB!s involving this propellant. It is not clear whether these kB!s are the fault of the propellant or the reloader, but it is clear that they are occurring in disproportionate numbers. [See Annotation #1]

Dean Speir and Frank James have reported that there are at least four discrete propagations of AA#5 in the U.S.A., variously manufactured under the same label by IMI, Olin, Beta Chemical (Norinco) in China and Lovex in Czechoslovakia.

Another poster has identified VihtaVuori N350 as a potential problem. As a rule, you should always track the lot numbers of your propellants, and when using a new lot (or to be even safer, a new canister), you should back off the power of your loads and slowly increase them until you have verified the safety of the new lot.
Don't use cast lead bullets at all, or at least be very careful about lead buildup if you do.
Religiously follow all the other safety precautions associated with normal reloading procedures. Take special care not to load a double charge.

Annotation #1 Accurate Arms' current reloading guide contains the following statement regarding .40 S&W pistols and supported/unsupported cases:

"In recent years it has become very apparent that there exists a situation regarding some pistols chambered for the .40 S&W cartridge. Some of the pistols currently available to shooters may not provide complete support to the case when a cartridge is chambered."

"This information [AA's load data] is safe for use in firearms which provide complete support of the case. Failure to fully support the case with cartridges of such intensity may result in bulged cases, ruptured cases, separated case heads or other consequences which may result in damage to the firearm and/or injury or death to the shooter and/or bystanders."

"If you own a firearm chambered for the .40 S&W, we recommend you contact the manufacturer to determine if the case is fully supported."

"If your firearm does not provide complete support for the case, DO NOT USE Accurate Arms Company data or products to reload your .40S&W ammunition."

"This is the first time Accurate Arms Company has felt it necessary to place such a restriction on the use of our products, but the continued safety and welfare of the shooting public compels us to do so."

Annotation #2 In late 1995, Federal Cartridge of Anoka, Minnesota quietly undertook a redesign of their .40 S&W cartridge case to strengthen internally the area of the case web. While no one at Federal will address this for the record, it has been suggested that this move was dictated by the popularity of the .40 S&W Glocks, and the munitions giant's attempt to hedge against a kB! with any of their ammunition.

Federal .40 S&W rounds which may contain suspect casings may be identified as follows:

Lot number consists of 10 characters (mostly numbers).
In the 7th position, there may be a number or a letter.
If there is a number in that position, the ammo was manufactured with the old style (possibly defective) brass.
If it contains the letter Y (1995) or R (1996), the ammo has the new designed casing and should be okay.
If the letter H appears, then check the next three [3] digits (the last three in the lot number).
Ammo lot numbers H244 or below have the old style casings.
Lots H245 and above have the new style casings.

This information was provided by Federal Cartridge Company in September 1996.

Annotation #3 It was Law Enforcement/Gun writer Walt Rauch who first brought forth information that bullet set-back (such as often occurs in administrative unloading/loading) in the .40 S&W could raise pressures exponentially.

"This was first confirmed via a European cartridge maker (Hirtenberger In Austria) from information given to me by a high level Glock representative. 1/10" set back can cause pressures to double from 35,000 psi to 70,000 psi.

"Note this was achieved with factory ammo and without the detrimental effect of lead build up in the barrels. I also had 'off the record' confirmations of this from two U.S. sources, one governmental and one manufacturer."



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