Normally, with something odd like this we would take the manual welding approach, but being that these are plentious on an upcoming job, the uppers thought it would be good to try and shoot them. To answer your question about what keeps them from sliding when you plunge the gun?...in the past we had a machine shop make some attachments out of heavy brass with set/thumb screws to shoot curved deformed anchors(looked like a "J"), these attachments clamped to the piece. No, your post didn't hurt in the least, I'm always trying to keep an open mind about new ways to do routine or mundane tasks to speed us up without sacrificing any quality.
BTW, the ferrule we use is for shooting to the inside/outside of an angle as you said, but it is positioned at a 45° angle to the legs of the angle. Now the stud is shot in the flat position, with that, you are correct