If you can remove the rear of the action to see down the bore, you can just set it up and look down the bore and use the actual bore as the boresight. It's about as good as any to get you on paper and works fine for the optic IMO. It doesn't work on rifles you can't see down the bore on (unless you can use a borescope?).
I have one of those magnetic boresights that uses lenses and gridded target inside the boresight. You just pop it on and adj. the scope looking down the scope, overlay the reticle on the grid; what's nice about it is you don't need 25m. to set it up, it can be done in a bedroom. I never use this one, still in the felt bag with instructions if interested. It was seldom used but it wouldn't matter if it'd been used 1million times. It's pretty simple, one piece. (Let me know if you are interested in this, I don't use it anymore. It's a Bausch and Lomb IIRC and I'll let it go for a lot less than you get it for anywhere else just to get it out of the toolbox. Will trade for a KAC .30 QDC mount too.)
I have a military boresighter and it's as accurate as the mandrels are I guess --at least it allows for adj. of the laser. The mandrels don't come in a lot of flavors and some like the .30 fit awful tight. I can't see how a boresighter would be all that good if you can't spin it in though. They can vary a few inches or more between rifles of common calibers.
A gridded target is nice, I modify the ones the military uses --they make a blank one and I just fill in the grid where needed based on what the mfg. says. Outside of 6.5 and .338, I don't fool with any other rifle bores, so this setup comes in a lot of handy for me.
Since I shoot targets on large cardboards clipped to pallets arranged as stands, I have to be WAAAY off to not see where I'm hitting. I've yet to boresight one that was actually in the black on a military 25m target though, and I've boresighted more than I care to count. Always spin 'em in first too. So that's why looking down the bore is about as good as any other method for just a scope.