I recently acquired a 16inch flat top upper. No markings that I can find other than 556 in front of the front sight. Anyway, I tried an ARMS 40, GG@G rear flip sight, and a detachable A2 handle from a Colt M4 and everything hits high. I have the front sight post turned out as far as I dare turn it, and groups are still 2+ FEET high at 100 yards. Reflex sight worked fine on it.
I'm hoping somebody can shed some light on this.

Thank you in advance,
Aaron

You probably need a different detachable handle. From what I gather, they aren't all the same. If I remember correctly Colt and Bushmaster flattop uppers and detach handles aren't as compatible as those both made from the same manufacturer.

I've never had these problems, so I'm reciting what I've heard from memory. If I'm wrong I'm sure someone will correct me.

Ponyboy is correct about there being incompatability issues with carry handles. I have the same problem - to a lesser degree - with my Colt M4 flat top and ARMS 40 rear sight. If you post in the SIGHTS forum someone will give you directions to who makes a taller front sight post, I think it's Oly but not sure.

DPMS has a taller front sight.  See the following (if it works – jeez it’s long!):
www.shooterstore.com/acb/showdetl.cfm?&User_ID=1608248&St=2030&St2=-540208977&St3=260251484&DS_ID=9&Product_ID=11538&DID=90

Just ordered the DPMS ext. front sight post. I knew you guys would have an answer


Thanks,
Aaron