How Do You Line Up And Mark Holes For Scope Mounts?

[MIG21]

I am curious how gunsmiths line up, mark and drill holes for scope mounts on barrels or receivers. A friend of mine says they use a string looped fron the front sight to either the rear sight screws or a tang screw. This seems to be to crude for a profissional gunsmith to use and they must have a more accurate and faster way to do it.
Thanks,
MIG21

[mangun]

and ask those guys. Get their catalog, too. it's a wonderful "wish book" and it will teach you a lot . It's huge, and it's abou $6, refundable with your first purchase from them. They are out of Montezuma, Ioway. They probably sell some sort of drill jig, one for each given model of gun, which you carefully align on the receiver and under a drill press.