100y Range Report: Frustration... (Need Help)

[Indrid Cold]

So I finally got another chance to take the AR-10 out to sight in the scope. Needless to say, I was hoping for an easy time. Not so. The thing seems to be shooting relatively straight (not much left/right spread other than user error) but it's shooting *really* low. I'm not talking like, three or four inches low, I mean that most of my shots clipped the bottom of the target if they hit. Everything seemed to be mounted pretty tight - the ARMS scope mount is rock solid, ARMS rail isn't shaking... I had originally thought it was the bipod shaking around or something, so I took it off and had the rifle perched on a benchrest - minor difference. For the record, the first 20 rounds were Federal Gold Medal Match, the next ten were HSM Match Grade.

I know I'm not yet good enough to get 1MOA groups at 100y on my own, but by the same token, I'm not completely incompetent. After being more than slightly frustrated with the sighting issues, I took the Colt 6721 for a trial run with irons and was shooting ~3-4MOA groups at 100y (on the target ;) )...

Here's the equipment list -

Armalite AR-10 with stainless steel barrel & national match trigger
ARMS SIR #53
Trijicon ACOG TA55A 5.5x50 with BAC
ARMS #19 Throw Lever Mount for Trijicon ACOG
Command Arms UPG Grip
Command Arms SRS Stock
Harris Bipod

I know there's the option to adjust the scope, but I really don't think I should have to adjust the scope ~40 clicks up. Hell, I think the scope would break before that happened, if not max out way before then.

Thoughts/comments/suggestions?

[scouter27]

did you try adjusting the scope? you never know where it is when you get it. i have never mounted a scope that didnt need adjusted before it was on. sometimes its way off. you dont say how low, only more than 4 inches. 40 clicks would be 10 inches, thats a big paper, though it is possible. try making some clicks and see where it gets you

[Indrid Cold]

Well yeah - I'm saying that I think it's way out of the range of scope adjustment. The ACOG is in 1/6th MOA per click, and if I remember correctly, the target had a 12in marked radius. That would be a heck of a lot of clicks if the shots aren't even in the target circle.

I'm thinking about trying the mount they sent me with the ACOG, just to see if it makes a difference, and then I'll start fiddling more with the scope.

[FirstFreedom]

Scopes will have anywhere from 200 some-odd clicks to over 500 clicks, so 40 is not that much. Having said that, when you are shooting THAT low, there may be something wrong. Maybe not though. What I do (at home) is take the scope, and turn the elevation knob ALL the way to one end of the spectrum until I feel resistance. Then beginning counting the number of clicks until I get all the way the other way, to find out the total clicks. Then divide by 2 to get the halfway point, and count back to the 1/2 way point. Repeat process for windage. Then I use an optical boresighter to see where I'm at. If it's more than 4 or 5 increments away on the Leupold optical boresighter, then I think thee might be a problem, and consider angle-loc rings, shims, or more likely, better/proper base & rings.

[gyp_c2]

...maybe your mounts aren't level...Bore-sight it and make sure everything is copasetic...Start from scratch or try another mount...get a baseline...http://emoticons4u.com/smoking/rauch06.gif

[Art Eatman]

First thing, center the crosshairs. Click all the way to the top; then all the way to the bottom while counting the clicks. Then go back halfway.

Shoot and see where you hit. If you're still way low, odds are that the mounts are the problem. The front base isn't high enough, or the rear is too high.

A solution is to shim the front mount of the scope, slightly. Brass shim stock works. 0.002", one piece at a time. If you get toward 0.010, you might need to take a dowel rod the diameter of your scope tube, wrap it with fine sandpaper and hone the rings so you don't crimp the scope when you tighten everything into place.

Art

[Indrid Cold]

Thanks Art :) I centered (I believe) the crosshairs last night. The total was around 400 clicks up/down so I put it at 200, and we'll see where I shoot afterwards. Hopefully I can get out to a range sometime soon.