I got my polygonal barreled 40S&W’s when the
Urban Legend ”lead bullets cause Glock and other polygonal-barrel KAGOOMS”
was being wildly bantered about on many forums, with very little truth to the mix. Before reloading lead, I did extensive research and discussed the problem with some well known gunsmiths and the Glock people at the SHOT Show. Both sphincters on every Glock staff were tighter than a bull a$$ at fly time. Nice folks, but NO HELP THERE! But they did make a valid point. Glock pistols are tremendously popular, and by shear weight of numbers you will have more “supposed problems” (their words).
There was no single factor that caused the problem; there were combinations of contributing factors. The shortest oversimplification is, “Glock KABOOMS were most commonly caused by lead buildup which could have been avoided with frequent inspection and cleaning of the chamber and barrel.” Just how often is frequent??? Every 100 rounds is anal, every 200 rounds is prudent??????? Hell, I’ll err on anal until I get some data to increase or decrease.
Problems:
Unsupported Chamber - Glock started with loose chambers with a small grove at the rear in the 6 o’clock position, thus the case was not touching anything at that point, it was unsupported. If the pressure is sufficient and/or the case weak, then it will either expand into the unsupported portion of the chamber or will rupture.
Firing Out Of Battery - Means the weapon will fire when the slide is not completely forward; therefore, the cartridge brass is not properly head spaced against the front of the chamber. Glock violently denies their weapons do this. However, everyone I know with an older Glock will tell you they do.
Lead Bullets – the lead needs to be at least a Brinell hardness of 19. Velocities should be kept under 1000fps.
So what causes the KABOOMS?????? The common factor of kabooms was usually case failure, and most of the failures were with reloaded cases. But remember that factory rounds cause good numbers of KAVOOMS every year as well.
Glock’s research of KABOOMS showed a build up of lead at the point of head-spacing. This caused the cartridges to be progressively set farther back in the chamber farther and farther as more rounds were fired. The design of the older Glocks allowed them to fire (fire out of battery) these rounds which were set back. If the pressure were sufficient, the case would rupture.
What factors can cause over pressure????? Obviously an overloaded round will do nicely. Lead bullets will cause leading in the barrel and the chamber. The degree of build up and the number of shots required to reach overpressure will vary wildly with lead composition/velocity/powder/lube and so on. The leading of the chamber in combination with the increased pressure of a leaded barrel can cause the case to rupture. There are lots of other factors, but will not be discussed here.
Shooting jacketed bullets after lead in polygonal barrels is controversial. Does it clean out the lead??? It is theorized that in reality the jacketed bullets irons the lead to a shiny flat coating and the bore is decreased.
Bottom line. Shooting lead in polygonal barrels is safe as long as you use hard cast bullets, check the chamber and barrel for leading frequently, and clean the weapon more frequently than you would with jacketed.
