ok fellas i'm sure this has been cussed and discussed but i need to know for my specific weapon and needs. ok i'm putting together what i guess would be called a designated marksman rifle. it'll be a colt ar15a4 20" rifle in 5.56mm with a leupold vx-6hd 1-6 with the firedot ret and cds turrets. i'm planning on shooting the black hills 77 grain otm load going round 2,750 fps at the muzzle. i'm also planning on using the adm delta cantilevered mount. the shots will be 600 yards and in. so, what are y'alls thoughts on 0 moa vs 20 moa cant for my needs? the leupold has 170 moa of travel so that'd be what 85 moa up and 85 moa down? my plans are to zero at 100 yds and dial from there to 600 yds. what say y'all please?

Big Ed

It can't hurt.  It may not be necessary, but it can't hurt.  You will never make use of all of the downward adjustment available in the scope.  

Do they offer a 10 MOA?

pretty sure its offered either a 0 moa or a 20 moa. most of my shots will be 0-440 yards with a little 440-600 yds thrown in on occasion.

I would get the 20 MOA version.  No real downside.

ok fellas thought i'd update this thread with my final decision. i did go with the 20moa ADM mount as i really didn't see a downside to it and it'll come in handy if i ever wanna push out past 600 yds or if i wanna go more mag for longer range. i just this past sunday eve sighted the magpul buis in for the 50-200yd zero. i know thats controversial too so...........

Big Ed

Not sure about controversy, but I sight everything @ 50 yards unless it states otherwise in the manual (re: BDC)

Zero both your scope and BUIS at 50. That gives identical holds. Otherwise you will have to dial your elevation turret to 200 to have a 50 yard zero, which takes it off of the lock.

If you keep a 100 yard zero you will screw up your close range hold overs when using 1x up close. This also frees up a few extra clicks on your elevation turret for the BDC to reach 600 on the first rotation, no matter your ammo choice.

You have zero reason to choose a zero distance other than 50 yards for both that optic and your BUIS.

There was no need for the 20 MOA mount. It just puts your optical center, which has the best image quality, only available at 500+ yards instead of point blank to 100 yards. But you probably won't notice anything negative with that scope.

Do not kid yourself and think you will shoot 5.56 past 600 yards. It sucks for that. Especially in any wind at all. A zero MOA base would have dialed you to dial 800 with that scope in 5.56 even with a 16" barrel... and past 800 the 5.56 bullet goes transsonic and gets unstable anyway. 20 MOA bases are for shooting beyond 800 yards and usually for beyond 1000 because a 10 MOA base gets most guns to 1000 that will really be effective at 1000.

A good rule of thumb for base selection:

0 MOA base = under 800
10 MOA base = under 1000
20 MOA base = over 1000

And finally... a 1-6 VX6 is a great optic and will be great... to about 300 yards. Past that, you will be wanting more magnification, a bigger objective, and adjustable parallax. Well, if you care about group size or shooting at 2 MOA targets. If you only shoot torso sized billboards of steel, it will work to your intended distance of 600 just fine.