[Lynn Eades]

Without the benefit of trying others, I would guess it to be about the right size. I/ we have made up all the tooling (snaps) It will easily smear the rivetlike warm butter if not held square on. We made the long stuff so we could get into the corners without changing the angle too much. We certaintly need some mass on the back side of the plate. Experimentation is required as there are lots of variables.
We started with 12mm of rivet sticking out past the plate, and have upped it to 15mm(this makes it harder for the guy on the gun) this is for countersunk holes (like at the bottom of the hull side plate, to the floor.

My holes are two drill sizes bigger than 3/8". we grind a small bevel on each rivet.

I was hoping the two pens were similar. It is my gun that is bigger. (no other comments!)