Rifle Scopes ACOG problem

[Raven FAC]

I recently bought an "demo model" TA-01 ACOG sight for the fixed carry handle AR.

Prior to mounting this, I had a conventional scope mounted on this 20" HBAR rifle and had no problems with it.

When the ACOG was mounted, the elevation would not adjust. Windage would adjust fine, but the point of aim would not move for elevation at all. I sent it back to Trijicon, and they graciously adjusted it, and now the scope does adjust for elevation, but it won't go low enough--at 10M (the location that I use to boresight the optic with a laser boresighter), the red dot of the laser is still a solid 10 inches above the aimpoint in the optic and I cannot get it any lower. Short of sending it back again, can anyone suggest anything that I might be doing wrong or offer an idea for a fix that I can implement? It's frustrating as hell to spend the money for a tool like this and not be able to use it.

 

[deadly0311]

Re: ACOG problem

why 10m? Shoot it at 100 and then see from there. Likewise, mounting it on a carry handle already throws a curveball, you have essentially already taken away some of the adjustment range just by having it so high over the centerline of the bore.

 

[dieselten]

Re: ACOG problem

If it is a carry handle mount you can easily shim between carry handle and base of acog. shim it behind the screw to get more distance. Shim in front of screw if scope if poi is too high. you can cut strips of just about anything that will fit in the track of the carry handle, plastic would be just fine. Start with about .010" and add or subtract from there.

 

[ORD]

Re: ACOG problem

When you got it back from Trijicon, did you bother testing it at 100m to see where you were hitting? Generally, when an ACOG leaves the factory (whether new or from a service return), it is pre-adjusted for an approximate zero at 100m with the ammo/rifle the ACOG was designed for (in case of your TA01, 55gr FMJ from a 20" A2).

The first thing to check is whether your mount/screw is tightened down all the way and ensure that the base of the ACOG is properly seated in the carry handle's sight channel. I have seen several that didn't get cranked down properly that allowed the ACOG to sit even higher than usual. If that is a go, then your scope should adjust just fine to get you zeroed at 100m (especially since it just returned from Trijicon who gave it a clean bill of health).

Second, make sure you are using the proper ammo to run with the TA01 (see above).

Third, move the @#$% thing out to 100m and quit screwing around at 10m.

Finally, if you still can't get on your POA at 100m, then you'll need to shim up the area between the bottom of the ACOG and where it sits in the sight channel on the carry handle. Shims behind the mounting screw (toward the back of the rifle/ACOG) will force the front of the optic downward, thus getting you on target). Use strips of aluminum (cans/jars/etc.) and go slow.

(BTW...if you have to resort to shim...it is a safe bet your carry handle is out of whack and not the ACOG itself).

 

[Raven FAC]

Re: ACOG problem

Sorry guys, I just had leg surgery before the optic came back and won't be getting out to a 100M range for a couple of weeks. Prior to sending the optic off, I had fired it at 100M and could not get it on paper. I also could not get it on paper at 50m or 25M. Right now, I'm using a boresiter off my workbench and shooting the laser as far as I can, but Trijicon customer service says that at 10M, it should be 3" above point of aim for a 100M zero and I cannot get it anywhere close to there.

 

[EXTREMEPREJUDICE]

Re: ACOG problem

I've had this problem when the base of the ACOG would not fit down fully into the slotted top of carry handle. I could not tighten the mounting screw enough to fully seat the mount. The resulting gap created an angle, similar to a MOA base. I used a pressure clamp to "mash" the ACOG base down for a tight/complete fit (slightly expanding the carry handle) and that solved the problem. That optic is designed to work with a carry handle and shouldn't be a problem for you to zero, 10 in. at 30 meters is way off. Good luck!

 

[Lumpy Grits]

Re: ACOG problem

Is your AR a "mutt" but chance ?
Who built it?
LG

 

[Raven FAC]

Re: ACOG problem

Rifle is a factory Bushmaster, bought new by me 3 days before the 1992 AWB became law.

 

[Raven FAC]

Re: ACOG problem

The fit is extremely tight. It took a bit of coercion to get it to seat. (Just some healthy raps with the palm of my hand--no hammering.) I'll take another look at that.

 

[ORD]

Re: ACOG problem

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Raven FAC</div><div class="ubbcode-body">Sorry guys, I just had leg surgery before the optic came back and won't be getting out to a 100M range for a couple of weeks. Prior to sending the optic off, I had fired it at 100M and could not get it on paper. I also could not get it on paper at 50m or 25M. Right now, I'm using a boresiter off my workbench and shooting the laser as far as I can, but Trijicon customer service says that at 10M, it should be 3" above point of aim for a 100M zero and I cannot get it anywhere close to there. </div></div>

Approx. 3" is correct for a 25m POI with a 100m zero, but you should be able to get the ACOG sighted in without going to either extreme of the adjustment range which brings me back to my point (and the point others have raised) that it is likely a mounting problem with the ACOG not properly seating in the sight channel on your carry handle. It could be that you just don't have the ACOG properly fitted into the handle or that it isn't tightened down properly against the handle. It could also be that your carry handle is out of whack in one respect or another whether it is not allowing the mount to seat properly or it is mis-manufactured in such a manner that it is causing your ACOG to cant upoward when the mount is fully seated. Either way...it sounds like a rifle problem and not an optics problem.

This may be an issue that went unnoticed with a standard rifle scope/mount/rings because a standard rifle scope likely has more internal adjustment than the ACOG which was designed to be sighted in at 100m and used with the BDC reticle at entended ranges instead of using the internal adjustments on a traditional rifle scope for dialing in the scope for bullet drop.