While most of us can easily pull out our bolts and bore sight, well.... through the bore, there are plenty of actions and firearms where that just isn't possible or easy. And of course side-arms also need to be zero'd when changing sights or adding optics. Laser bore sight kits have gotten quite inexpensive but as many of us who have tried them out, found them to often bee less than 100% dead nuts center on your bore.
Well, there’s a certain amount of looseness in the tolerances, from the laser diode to the straightness of the stem, to threads of the screw on the caliber adapter. It’s actually quite normal that they’re just a few degree’s off. What?!!! you might think "is this useless junk?" And many have returned them thinking that.
But by using a little practical geometry we can get around this imprecision. By rotating the bore sighter while attached to your barrel, the laser dot traces a circle around the center of its axis; your barrel. You can either estimate the center of that circle or simply position the dot at the nadir of the curve, you can aim the vertical/elevation centerline with your barrel.
This will almost certainly get you on paper if nothing else. Once you get holes on paper you can make finer adjustments to zero your sights.
I haven't found the expensive laser sight kids from "US brands" like Bushnell or Wheeler any more accurate. Here's some cheap laser options I've used. There are many others.
WOLFROAD BORE SIGHT KIT
https://amzn.to/3t8CBle
MIDTEN BORE SIGHT KIT
https://amzn.to/3JSQc61
