1) The very basic pistol grip is proprietary, with two holes (one for a pass-thru pin from the trigger group, the other — toward the rear — to mount the Allen screw). Standard AR grip options will NOT work as their hole(s) does not line up at all with where the screw mount would need to be. I did quite a bit of modification and drilling to get a Hogue grip mounted (which was worth the effort). Shame they couldn’t have made that part STANDARD!
2) The recoil buffer tube, although mil-spec diameter, does NOT thread into the receiver the way a standard AR does. Instead, the castle nut is mostly for looks, because that tube mount to the receiver via an Allen screw that can only be accessed by removing the end-cap at the end of the tube. Bottom line, you can’t change tubes out, but you CAN replace the 5-position butt-stock with a mil-spec after-market version. I first tried the CAA version which went on easy, but was WAY too wobbly when fully extended. I then went to the Mag-Pul CTR which has the lock-down lever, which fit much better, and took the wobble out.
3) Very impressed with the accuracy. The free-floated barrel of the “tactical” version (quad rails) certainly lends to this.
4) Trigger pull is rather heavy, but consistent with little play or over-travel. Didn’t take long to get used to it.
5) I wish there was a way to lock the bolt open (other than inserting an empty mag then pulling back the charging handle). The lever that would normally do this on an AR, is also on this rifle, but it is cosmetic and non-functional. Hmmm…
All in all, I am pleased with this rifle, and proud to finally own at least SOME type of Colt AR. I hope you find these observations useful.