There are several ways that I have used at different times the two I like best are pull the breach plug insert laser pointer [just a regular pointer ] set up a target at 20 yds move the cross hair on to the spot this works best at dusk or after dark. The other way is very similar with a pen light setting at 20 yds. You can lock the rifle down in a rifle vise or pad it and use a regular portable vise and set your target up at 20 yds and move it so the bore centers then move your cross hairs to center. Lee