I've got a bunch of different snap-caps in different cartridges, most of them A-Zoom(they last a lot longer than others I've tried. Couple of days ago I loaded some .380 caps into a magazine to check a pistol I'd cleaned and cycled the slide and oops! Two or three times out of each mag the extractor wouldn't extract; sometimes had to work the slide back & forth several times to get it to grab.
Checked the extractor, couldn't find any problem. Finally, just to check(Note: this is one of those BE DAMN CAREFUL IF YOU DO THIS things) I loaded the mag with ammo and- being very careful where my finger was- cycled the slide. And no problems.
Loaded the snap-caps, problem. Ammo, no problem. I've never had this happen before; apparently the rim or something on the caps is just enough different that this occurs with this pistol. I guess I need to make some dummies with cases and bullets just for testing things like this if they occur in the future.
Updated: took that pistol to the range today, and it worked flawlessly. But it still has the problem with those caps.