A prick-punch is a sharp metal punch, as opposed to a center punch, which has a blunter point to more closely match the point of a drill. The broader center-punch dimple allows the drill point to center accurately in the punch-hole.
A prick punch provides a slight accurate dimple on the metal right where you want it on the layout lines. You then place the center punch in the prick punch hole and strike it with the hammer. Trying to accurately punch a dimple directly with a center punch is difficult because it is so blunt.
There are automatic spring-loaded prick punches, where a hammer is not needed, you just push down on the body on the punch and it places the dimple
--bink! --right where you want it.
I went around the inside of the bushing at 120° for each punch. Did not seem to affect the sighting, but that's because I'm a superb, expert, and experienced machinist and could punch the marks with outstandingly accurate symmetry just by eyeballing the 120°.
(It was also dumb luck, since you couldn't call it smart luck.)
Terry, 230RN