[bwhite]

A Glock will certainly fire with the slide immobilized. If the slide cannot move with respect to the frame the current round will not be ejected and the next round will not be chambered, but it will certainly fire the chambered round. It is not clear from "grab the whole barrel" what you were doing. Glock is like many (most?) semiautos in that the trigger cannot be pulled when the slide is not all the way forward, is that what you meant? That you could yank the slide out of battery and hold it there, thus preventing the trigger from being pulled?

If you intend to replicate your experiments in the future, you can explicitly seat a snap cap in the chamber and leave the magazine out (no mag safety on the Glock). That way you are still violating rules 2-4, but possibly not rule 1.

[blasdel]

It's pretty clear he meant that he was holding the slide back, preventing the hammer from moving forward.

But would that always work on a Glock, which has an odd striker arrangement instead of a traditional exposed hammer, and doesn't have a way to decock it without pulling the trigger?

[bwhite]

Holding the slide is not what prevents the hammer from falling. A semi-auto handgun with an exposed trigger that is placed out of battery has its trigger immobilized by mechanical linkage, regardless of the hammer's position.

Because of the way Glocks have their lug linkage, many will actually fire even when slightly out of battery. Knocking the slide back 1/10" and holding it there is probably not going to be sufficient to disengage the lug that prevents trigger pull.

Even if one could manage to pull the trigger with the gun significantly out of battery, I imagine that this would be a non-event with an exposed hammer because as you say, the hammer would fall onto the slide, not the pin. Still, firing out of battery would seem to be a function of the linkages, not striker-vs-exposed-hammer-ness.