I went thru about 3 different brands of laser boresighter from Walmart til I got one that worked. I used it to zero my ACOG, Aimpoint, and Eotech equipped ARs with. Yeh, I've got a really bad case of black rifle disease. Recently it's expanded to green and tan rifle diseases too.
The laser I've got now works great. It's a Laserlyte brand. It's a red anodized aluminum shaft with the laser in one end and one of several adjustable split plastic collars that secure the other end centered up in the bore. You find the right sized plastic collar and adjust it till it just will fit down the bore. Then you push the device as far down the barrel as possible till the crown of the muzzle is snug up against the cone shaped back of the laser module housing. All you have to do next is turn the thing on, point your unloaded and safed weapon down range at a target and align the sights dot, doughnut, reticle, etc... on the laser dot.
Note: you can't see the laser outside in the middle of the day. Do this in the evening or real early in the morning. Unless you have four arms you better have a rest or gun vise to lock the weapon down in while you twiddle the adjustment knobs.
Avoid laser boresighters that have a laser that goes in the chamber of the weapon and require you to put a collimnator in the end of the barrel. The cheap ones (less than $150) suck and don't work. The collimnator should have a lense in it to focus the beam. The cheap ones are just steel tubes with a small hole thru them. The two I tried would create 3 or 4 big blurry dots. Without the barrel collimnator you get a huge red circle on the target that is equally useless. Some of the more expensive units may be different, YMMV.
