We always advise students coming to our classes to bring a second gun just like the one they plan to use, so if the first gun breaks they can still use the same holster, magazines and ammunition to finish the class. We base this advice on the fact that in just about every class we see a gun break—not malfunction, but suffer a broken part that deadlines the gun until it can be repaired.
Last weekend we were in Oklahoma teaching our annual EDP course with Southnarc and William Aprill. We did not have a gun break in this class (unless you count a front sight that flew off mid-drill), but we did have a malfunction that had the same result as a breakage, at least temporarily. During a shooting drill, a fired case wound up backwards in the chamber of a Glock. This kept the slide from going into battery, so the student immediately did a TRB, per doctrine. No luck. He then tried a double-feed clearance. Still no love. At that point I stopped him, fearing there might be a bullet stuck in the chamber from a squib load. Only then did we see the backward empty case in the chamber! I broke a ball point pen inserted from the muzzle without dislodging the case. The student had to take the gun off the range and find a brass cleaning rod and beat the case out of the barrel.
This is a good reason to bring that second gun to class. It’s also a strong reminder of the wisdom of wearing a back-up gun (BUG) when out and about. If this malfunction occurs in a fight, you won’t get it fixed in your lifetime.