I have an Aimpoint Comp ML2 in a LaRue M68, coupled with a GG&G BUIS with locking detent. I have the setup lower third co-witnessed and sighted in for 25 yards.

I recently took my setup out to some property that my mother owns and set up some pop cans at about 80 yards. At that distance I had to put the dot right below the can to make them explode. If I put the dot on them I could see dirt kicking up just above the top of the pop can. Just to make sure it wasn't operator error I rested my M4ergy on my pickup truck and I got the same results? What gives?

I thought a bullet would hit lower further out, rather than higher????

Hope to get some help, thanks!

If you sight in at 25 you're going to be high all the way to around 300+ where the bullet drops back down past your line of sight again.

Quoted: I have an Aimpoint Comp ML2 in a LaRue M68, coupled with a GG&G BUIS with locking detent. I have the setup lower third co-witnessed and sighted in for 25 yards.

Zeroing at 25 gives you a VERY high trajectory (and doesn't come down till almost 400y)

Zero it at 50y, You'll find the results are MUCH MUCH better.

In the meantime visit: Zeroing Methods and read the articles and look at the charts.

Better yet, read Zak's explanation of optics for practical long range shooting.  Should still be on the first page of the optics section.