Originally Posted by glock_19guy1983
This. 10mm headspaces on the case mouth, running a 40S&W case in a 10mm chamber means that the extractor is the only thing holding it in.
Yep, it will work until it doesn't. I'm not sure, but I would think it could result in the case head separating and some brass and crap blowing out of every hole, sooner or later.