Technically, I think the term "bullet drop compensation" better fits what this means in the game (which I haven't gotten in the mail yet) than "zeroing".
I have an ACOG (TA01 4x32) on my own rifle in real life, and it has a reticle similar to the one for the ACOG in original Arma 2, though it goes out to 800m/yds vice the 600 in the game. On my TAD to Iraq a few years back helping out the Army guys, I was issued an M16 (A2, unfortunately; I was hoping it'd be an A4), and no one had a problem with my hooking all my extra gear to it once I had finished the rifle marksmanship part of the Individual Augmentee training, though being an officer in a somewhat unique assignment probably helped.
As several others have already mentioned or suggested here and in other threads, with the ACOG, you range targets by bracketing the torso of a human target with the horizontal lines of the crosshairs, i.e. if the guy you're aiming at is as wide as the "4" line, you place the intersection of the "4" line and the vertical crosshair on his center of mass and fire. (Of course some guesswork is involved if he is standing at an angle, of a smaller/larger build that normal, etc.)
When have zeroed mine, I just did it on a known-distance range and did the usual drill to make sure the rounds hit the target at 100m at the center of the reticle (when the wind was reasonably low), and everything else more or less lined up. Note that the reticle is actually calibrated to a specific barrel length, type of ammunition, height above boreline of the scope, etc., and some reticles are in meters while others are in yards; IIRC if you're buying one directly from Trijicon you can actually special order reticles when you order a scope to match your own configuration. Most 5.56 or .223 ammo is close enough that you don't have to compensate much, though you should ideally rezero if you are using a different type or lot of ammo, and you want to remember the slight offsets at each range. For example, if you're using a TA31RCO, which is calibrated for 62 grain M855, but are shooting a case of 55 grain M193 rounds (in SoCal, most civilian ranges don't let you use steel core rounds due to the sparking hazard in dry weather), the bullet won't fly exactly through the 300m line on the reticle at 300m out, so you have to remember to hold it off by an inch or what not; of course this doesn't matter that much if you're trying to hit a human torso in a combat situation compared to shooting a 1-inch bullseye (or a tin can or something) at the range. With wind using an ACOG, you just have to deal with wind by using guesswork and hold-offs (Kentucky windage), though at the ranges you're working it's generally close enough.
As another note, most of the US military people I worked with in theater had a decent working knowledge of the optics of their weapons if they had an optical sight, and I didn't know of any prohibition on adjusting them as needed; their sights would have been zeroed before they deployed, and for the non-snipers there wouldn't be any need to adjust them unless some problem was noted in a practice shoot or in an actual engagement.
Zeroing/Adjusting Weapons in OA
in ARMA 2 & OA - GENERAL
Posted
Technically, I think the term "bullet drop compensation" better fits what this means in the game (which I haven't gotten in the mail yet) than "zeroing".
I have an ACOG (TA01 4x32) on my own rifle in real life, and it has a reticle similar to the one for the ACOG in original Arma 2, though it goes out to 800m/yds vice the 600 in the game. On my TAD to Iraq a few years back helping out the Army guys, I was issued an M16 (A2, unfortunately; I was hoping it'd be an A4), and no one had a problem with my hooking all my extra gear to it once I had finished the rifle marksmanship part of the Individual Augmentee training, though being an officer in a somewhat unique assignment probably helped.
As several others have already mentioned or suggested here and in other threads, with the ACOG, you range targets by bracketing the torso of a human target with the horizontal lines of the crosshairs, i.e. if the guy you're aiming at is as wide as the "4" line, you place the intersection of the "4" line and the vertical crosshair on his center of mass and fire. (Of course some guesswork is involved if he is standing at an angle, of a smaller/larger build that normal, etc.)
When have zeroed mine, I just did it on a known-distance range and did the usual drill to make sure the rounds hit the target at 100m at the center of the reticle (when the wind was reasonably low), and everything else more or less lined up. Note that the reticle is actually calibrated to a specific barrel length, type of ammunition, height above boreline of the scope, etc., and some reticles are in meters while others are in yards; IIRC if you're buying one directly from Trijicon you can actually special order reticles when you order a scope to match your own configuration. Most 5.56 or .223 ammo is close enough that you don't have to compensate much, though you should ideally rezero if you are using a different type or lot of ammo, and you want to remember the slight offsets at each range. For example, if you're using a TA31RCO, which is calibrated for 62 grain M855, but are shooting a case of 55 grain M193 rounds (in SoCal, most civilian ranges don't let you use steel core rounds due to the sparking hazard in dry weather), the bullet won't fly exactly through the 300m line on the reticle at 300m out, so you have to remember to hold it off by an inch or what not; of course this doesn't matter that much if you're trying to hit a human torso in a combat situation compared to shooting a 1-inch bullseye (or a tin can or something) at the range. With wind using an ACOG, you just have to deal with wind by using guesswork and hold-offs (Kentucky windage), though at the ranges you're working it's generally close enough.
As another note, most of the US military people I worked with in theater had a decent working knowledge of the optics of their weapons if they had an optical sight, and I didn't know of any prohibition on adjusting them as needed; their sights would have been zeroed before they deployed, and for the non-snipers there wouldn't be any need to adjust them unless some problem was noted in a practice shoot or in an actual engagement.