Don't listen to the reviews complaining about arbor fitment. - Bushnell Laser Boresighter w/ Arbors

Some reviews say the item wobbles around in the bore, the arbor doesn't fit snugly. That was my initial experience too, but here are two tricks that I think people overlook:
Tip 1- When you find the biggest arbor that fits into the barrel, it WILL be loose. BUT, keep turning the arbor screw further into the laser body, until the plastic starts to expand outward, which increases the diameter of the arbor. Once you find the sweet spot, back the screw out a small amount and fully insert the tool into the barrel. Very gently turn the laser clockwise to snugly expand the arbor inside the bore. It will fit nice and snug, and be very close to square with the barrel.
Tip 2 - When turning the front end of the tool to make the laser power up, be sure to tighten it all the way down (without turning the main body of the tool). If you don't do this, the laser beam will not be square with the body of the tool.