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Zero at 200 then shoot at other distances and see where you hit, right the results down.
Or zero at 100 yards and do the same because unless you're only concerned with getting hits somewhere on a full sized silhouette, you need to forget the 25, 50 or even the 36 yard zero. You need to know exactly where your gun hits at the distances you want to shoot in the conditions you are in.
I have preached this shidt forever. Many hearing it get the 500 yard stare and start saying "But..but...Youtube..."
If they haven't started slobbering yet, I explain the .mil zeroing regimen was carefully worked out with with rifles, ammunition and sights all held to strict government standards. Change any component and it all goes out the window. That's why the zeroing and sight adjustment protocols are different for the M16 than the M4. You've changed the barrel length, sight radius and terminal velocity and everything related to zeroing changes with that.
AR's today, with widely disparate sighting and ammo combinations, have rendered it about useless. Regardless of the rifle type, I work hard to get a perfect 200 yard zero from the bench and then I haul the damn thing off the range. From then on I shoot from field positions (offhand, sitting, field expedient rests) which tells me what I can do with that rifle out to the farthest distance I might need to use it. If the results don't suit me, I know the problem is me. So I bust my ass and work harder to improve.
