Leupold zero point bore sighter - Leupold Zero Point Magnetic Illuminated Boresighter - 59012

Very simple to use and will fit any caliber rifle. Most difficult thing is centering device along center of bore so that windage adjustment is accurate. I have it to be very accurate and I am always on the target at 100 yards.
Pros: Easy to attach. No varying caliber studs
Cons: None

This review was written in the old system and had content requirements that are different than reviews written today.