Sightmark gets it done - Sightmark Laser Bore Sights

Other than being a little tricky getting the button cell batteries installed, these laser bore sights are excellent. If you want to get "on-paper" quickly with something you can trust, these are great to have. The downside is you need a separate one for almost every caliber you shoot but there are exceptions (like .270 Win, 25-06, 30-06). I have 4 different Sightmark units and they are truly helpful and easy to use. Construction is solid machined brass so they have held up very well for me so far. Getting a newly mounted scope sighted in is quick and easy with the laser bore sight. Just put in the batteries and put the device in your chamber and aim at something 40 yards away or so. While looking through the scope, turn the elevation and windage to put the crosshairs on the laser dot and you are going to be better than "on-paper" at 100 or 200 yards easily. Saves ammo and gives me confidence before I start shooting. Also great to check your rifle with before heading to the woods to make sure the scope didn't move.