Rifle shooting far left?

[Wake27]

I have an AR I bought used from someone here a little while ago. I know it wasn't straight from the factory since the upper and lower are different companies, but I don't know how much of it he pieced together. Everything looks good on it (including sights - MBUS) but when I went to zero it, it was hitting far left. The target was an paper IPSC target (http://www.amazon.com/Law-Enforcement-50-pack-IPSC-Targets/dp/B0001FAANQ/ref=sr_1_1?ie=UTF8&qid=1344010185&sr=8-1&keywords=paper+idpa). Its a large target and I had it placed at 25 meters. I fired three rounds, and the grouping was fine, but they were on the very left edge of the paper. Long story short, I couldn't adjust the rear sight far enough to the left to zero. The aperture that was all the way to the side of the sight and would not move anymore. Also, when I did adjust it, the groups didn't shift at all - they hit in the same place.

I threw my EOTech 512 on, and while I was able to zero with that, I had to crank it wayyyy to the left. This has all been done at a static indoor range and I haven't really been able to mess around with it too much, but any ideas? I'm thinking it must be something with the barrel?

[Split66]

Lol nvm ;)

[seb5]

Does it have a standard FSB on or a rail with sights? Many times rails need to be re indexed to get the irons where they're supposed to be.

[3 AE]

If your groups are far left, you would want to move the aperture of the rear sight to the right to bring the group to the right.

[Wake27]

Does it have a standard FSB on or a rail with sights? Many times rails need to be re indexed to get the irons where they're supposed to be.

No FSB, just the DD rail with MBUS on top.


If your groups are far left, you would want to move the aperture of the rear sight to the right to bring the group to the right.

Yeah that's what I did. When I said left in OP I meant adjust for the rounds hitting left. If that makes sense...

[Aaron_B]

Is the rail itself canted? Had this same problem on a buddy's rifle and just loosened the bolts, straightened rail, and torqued to proper amount.

[LeroyRT]

I would completely loosen the rail, bolt it back up and try again.

[HKBanger]

I'd do what the above poster said and take the rail off completely, then mount it again ensuring that everything is aligned perfectly. Perhaps far fetched, but is the barrel itself possibly canted from somebody cranking on it?

[Wake27]

I went ahead and loosened all of the screws and then bolted it up again like you guys suggested. The rail didn't really seem canted before, but I didn't really look for that specifically before I started loosening it all. I also don't have the right torque wrench, but I read around a little and most members on here agreed that you don't really need it and just to crank it. I don't know if I'll be able to test it before tomorrow night but I appreciate the help, and please keep ideas coming just in case this doesn't work.