most say use this method. shoot at 25 yards and set your rear sight to 100. try to hit your target 1 inch low. this will be very close to dead on at a real 100 yards
they say 25 yards because most ranges will have that distance.
if you have access to a 100 yard range then use that next to verify. I had to tweak mine a touch but at 100 yards the target I was using was very small and I couldnt even see it in the sights.
for me ive found I shoot quickly, and when I do my hits end up being 1-2 inches high at 25 yards. So I set my front post to still hit 1 inch low at 25 yards but shooting fast. So just take that into consideration if it applies to how you shoot
I use a cheap $30 laser bore sight from midway, and I can set it at 25 yards at home and be dead on, this way I save some money on ammo. Plus that laser bore sight has tips to do most all calibers so it comes in very handy for all weapons. If you set up a car reflector, or reflector tape you can use the laser at 50 yards too, but the dot is pretty big. Never tried it at 100 yards
Also I read if you set to battle zero and shoot at 20 yards you want to be dead center of target