No laser necessary. Put the gun on some sand bags or other kind of solid rest. Remove the bolt. With your eye, center the target in the bore by moving the gun. Once centered, adjust the cross hairs on the scope to the center of the target. Double check the bore to be sure the gun hasn't moved. Do this until the cross hairs and the bore are centered on the target. Do this all at 50 yards.
If you've done it right, and you have a decent rifle/scope, the first shot will be within 2" at 50 yards.
I've done this several times with several rifles and all with the same result. No need to start at 25 yards and no need for a laser. The only gun I haven't been able to do this with was a lever action (can't see down the bore).