ACOG Scope for my 6.8


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SkinnyGrey
March 8, 2011, 05:38 PM
I have an ACOG scope mounted on my 556 AR-15. Now I am playing with the idea of mounting it on my 6.8 AR. This might be a stupid question, but will scope work just the same with the 6.8? I have heard that certain reticles are designed for specific calibers. Any info would be greatly appreciated.
Much Thanks!

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HorseSoldier
March 8, 2011, 05:40 PM
The BDC for an ACOG is set for a specific caliber and bullet weight, so it's not going to be a perfect fit. You'll have to figure out how the trajectory of your 6.8mm load varies from whatever caliber/bullet combo the scope is calibrated for (probably 5.56mm 62 grain M855) and then figure your new holdovers.

(For longer range work -- inside 300 you're probably not going to see enough deviation to shoot anything besides point of aim for the appropriate range.)

SkinnyGrey
March 8, 2011, 05:58 PM
But can I adjust it so it is a near perfect fit?

ny32182
March 8, 2011, 06:00 PM
The BDC is not adjustable.

Realistically it is probably plenty close enough out to the ranges most people shoot.

It is only an "estimate" anyway, unless you are shooting the exact bullet at the exact velocities it is calibrated for.

SkinnyGrey
March 8, 2011, 06:04 PM
i can't see myself shooting any farther than 500 yards. that should work?

68wj
March 8, 2011, 08:30 PM
Get out to a range and give it a try. Even with 5.56, you wouldn't want to stake a shot without some trigger time on paper first. Let us know.

HorseSoldier
March 8, 2011, 08:47 PM
i can't see myself shooting any farther than 500 yards. that should work?

There are various free ballistics calculators online, as well as published tables for most factory loads.

Your ACOG is probably calibrated for M855 green tip -- but may be set up for a 14.5" or 20" barrel. You need to figure out which, and then look up the bullet drop for that round and barrel combination at different ranges. Then compare that to what the 6.8mm load you're shooting does. The difference between one and the other is the hold over you're going to have to estimate when shooting.

Not a hugely complicated process, but something you'll have to do to get accurate results.

(For what it's worth, my recollection is that the 7.62x51 BDC calibrated ACOGs are very close to 6.8 Rem SPC, not requiring much shooter compensation at all. I think the difference with 5.56mm is somewhat more pronounced.)

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