Recently I purchased a bore sighting tool. First time using one. The model is a Mag Laser SL-100 by SLite. I used it today to bore sight a Savage 220 20ga shotgun and a Remington 870 12ga slug barrel. Both shotguns were scoped. At 50yds both guns were with-in 4" of the bull and needed only a couple of more shots to shoot 1.5"h. The instructions were simple and it carries lifetime warranty. Well worth the money spent.