Quoted: Can you get a good 300m battlesight zero with a .308? Or is the midrange rise too great for that distance, and some lower range all you could get? At what close range would you zero in at (like the 25m M-16 BZO)? I'm going to mount an Aimpoint on my M-14 and want to know what ranges it would be useful for.

At the top of this page is a link to important topics, one of which deals with M1A BSZ.

Your GI BSZ for the M1A is 250M, assuming two-legged targets.  

What you are really asking about is the Maximum Point Blank Range (MPBR) of your rifle.  The answer to that question is based on the radius of the kill zone of your target.

Once that radius is given, and knowing the external ballistics of the cartridge in question, your MPBR for your cartridge and target is the distance at which the rise and later fall of the bullet in flight spans the diameter of the kill zone of your intended target.  That is to say, from muzzle to maximum ordinate is 1/2 the diameter of the kill zone (1 radius) up, and from that point  (not midpoint of trajectory,BTW, but close) to minimum ordinate, in this case the target, or impact point, is another 1/2 diameter (1 radius) down.

Quoted: Lots of interesting info on the links. Thanks for pointing it out for me. So if the round strikes POI at 250 yards using the 25m target in the link, at what range beyong that will the bullet drop below, say, 12" or so? Using generic surplus military ammo that is. No BDC on the Aimpoint so I'm just trying to determine the maximum "point-and-hit" envelope for two-legged targets.

Using your iron sights, sight-in at a target @25M, using the procedure outlined in the links at the top of the page.

When POI=POA @25M, your rifle is sighted-in for 200 yds.  Adjust your iron sight elevation scale to reflect this, if necessary, again using the aforementioned procedure.

Now, turn your elevation up 2 clicks so that the wheel reads 275 yards.  Fire for effect, and note where the center of the new, 275-yd group lies.  Adjust your red-dot so that its POA=center of 200-yd group (first group), and the bullets' POI=center of the 275-yd group.  You're done, and both your irons and red-dot are calibrated for BSZ and MPBR for 2-legged critters.

You would be wise to mark the adjustment dials/wheels/knobs to reflect this setting.

Quoted: Thanks for the info! I shall certainly use it. However, in this thread I was asking about zeroing with the Aimpoint, not the irons. Specifically, if zeroed using the 25 yard target, at what range beyong that will the bullet drop below, say, 12" or so?

If POI=POA@200 yds, and assuming NATO ball, bullet drop is approx. 8.5"@300 yds, and approx 24.5"@400 yds.