Re: BSA Bore Sighter
I have witnessed more than a few guys at the range trying to sight in a rifle that was collimator bore sighted by a gun store or a gunsmith. They MIGHT get you on the paper at 50 yds and might not.
If the gun to be sighted in has a way to look down the barrel from the breech end that is still one of the best ways to align the scope or sights with the target. The laser style units that fit into the muzzle end of the barrel and put out a red dot on the target work fine too. In my experience the collimator bore sighter doesn't always work if done by the unknowing.
I bore sight my guns in my house, down a long hallway to a target stuck on the wall. The distance is about 50 feet. For looking through the bore I stick the gun in a rest, line up the bore with the target and carefully, so as to not move the gun, adjust the scope to the target center.
For the laser type you only need to stick it in the muzzle, shoulder the gun and adjust the sight or scope until the red dot on the target (a blank wall at 50 feet will do) matches the sights. The one I use is tapered closest to the body of the laser and comes with a set of adjustable collets that go on the end of the laser closest to the breech making for a secure tight fit to the bore. It is so designed that you will not hurt the bore if you are reasonably careful. No rest is necessary or desired and you don't even need a target pasted on the wall, just the wall.
All that being said, at $29 for the BSA collimator bore sighter how can you go wrong. If you keep records of how the gun sights or scope and the collimator end up then this would be a good way to assure your sights or scope have not changed with the environment or in transit on a hunting trip without firing a single shot. I can think of no case it would be an advantage to me so I'll stick to my methods and save the $29.