Simple question, are these worthwhile?  From a theoretical point of view, it would save some time and ammunition zeroing.   However, I've never had the chance to use a decent one, if such a thing exists.  If so, can anyone recommend a good one?

Thanks

I've seen probably a dozen "boresighted" rifles that were 1-2 feet off target, so I don't think so.



I do it old school: remove bolt and set the rifle/upper on bags, align the bore on target, adjust windage until the bore and sights agree, then add some elevation. The first shot is usually within 2" of center at 100 yards.

THIS.
Works every time.

Bore sighters and collimators haven't helped me get on target with a new combo. The method above is one way but it's been unreliable and harder than it needs to be and seems to consistently waste ammo. I used to do it that way before I learned an easier and more precise way. I set up at 25 yards, measure scope centerline height above bore centerline, shoot 1 round at the 25yrds target and measure how far from the POA the POI was, I adjust the scope turrets to bring the POI to be 1x scope height under the POA. Move to 100yrds and fire a confirmation group and adjust if necessary. Everything is based on simple measurements and there's no burning of excess ammo. It's also a great time to find out if you need a canted scope base or adjustable rings or whathaveyou.