There are too many cause and effect relationships going on when a double rifle is fired and regulated to use lasers to measure or indicate when both will converge. For one thing, the intensity or the loads can vary enough to throw the whole thing off, plus the gun rotates as it is fired meaning that the barrels won't be pointing where they were before firing. I turned down two laser pointers to fit into the muzzles of a 45 caliber rifle, thinking that that would put both barrels onto the same P.O.I., but it didn't even come close to working. The best they can be used for is to keep them on the same plane when fitting and soldering and you can use spacers or shims just as well and not have the hassle of messing with lasers. If you think about it, regulation is the act of making two barrels hit roughly to the same imaginary spot when they are fired. Neither barrel is pointed at that spot before firing. Any laser device used must be put into the muzzles of the barrels because the barrels are actually sprung or bent when they are finally finished. No laser put into the chambers is going to do any good at all. Bob H.