After much research and handwringing, I finally decided on an Oly SUM 16" A3 upper to mate to my Colt Competion HBar Match lower to make a handier rifle.
I just wanted to first thank everyone who took the time to answer all my questions and secondly to give anyone who is interested or going through the same process of making a choice an update on my findings. If you are not interested, stop here.
First of all, I was very impressed with the OLY upper, if not with their customer service. At times it seemed I knew more than their rep, and that is not saying much. It is an extremely fine piece of equipment. I went with the flattop upper, single rail front gas block and 16" Stainless Ultra Match barrel (not chromed) in .223 chamber, with their complete bolt/carrier assembly.
I will never be firing this unit rapid fire and will primarily use this as a truck gun at the deer lease for short and medium range varmint shooting, thus my choices for stainless, no chrome and .223 chamber-I am hoping to find a really accurate load and 5.56 was not necessary and possibly a roadblock to maximum accuracy.
I decided against fluting and a muzzle break for the same reasons - reports that these have a negative effect on maximizing accuracy in 16" barrels and the weight is not that much of an issue to me. After lugging that HBar and moreso that AR10T around, this thing feels great!
It mounted easily to the Colt lower - very tight & smooth, though the color was a bit darker - but still close and very well done. Excellent looking, really. The first cleaning out of the box was scary. This barrel was filthy! I had to use 3 different solvents to get the black out of it - though it was shiny and pretty just looking into the bore, patch after patch came out black. The rest of it was just fine - the bolt assembly wiped clean easily and oiled right up.
After finally getting it cleaned (easily 100 patches.. no kidding) I went through a long barrel break-in period. It has taken me three trips to the range so far. I started by the one shot, clean, next shot, clean method. I used Shooter's choice and Butch's bore shine and a very light coating of CLP on all the moving parts, though not during the firing/cleaning until I put it up for the day.
After every shot there was a surprising effort required to get a clean patch. I basically went through the same effort or more that I do on any AR after and extended shooting session - after every single shot! It probably took 10 - 15 minutes each time. You can see how this was time consuming.
I finally got 30 shots through it and went to the shoot 3, clean, repeat method and this time - again surprisingly, the cleaning effort got easier! It became much less effort to clean after every 3 rounds than one round. Weird, huh?
I just mounted an old BSA red dot I had laying around and got it on target pretty quick, though with the 4 or 6 MOA dot (I don't remember which it has) I was definitely not getting sub moa groups. But I didn't expect to during the breaking in process and it was on paper, so close enough for now.
After many questions here and from vendors, I decided on the ARMS #40-BUIS and DPMS front flip up for sights. They both fit very well and I am very pleased with their quality. They did not cowitness with the BSA, but I did not expect them too (more on that later) so no problem for me, but someone else may want to know.
What I found was with the front rail gas block is that I could not adjust the front sight to get a shot closer than about 8" low at 50 yards. They just did not line up right with that set up. As best I can tell the ARMS is windage but not height adjustable, so there was no help there.
So... a little filing on the front sight post and everything was fine. By now, my OKO sight arrived, I installed it and back to the range I go. I found it to be just a little too low to cowitness with this particular BUIS set up, though I like all the sights - they are all just fine - they just don't all line up well, so an OKO SCR4 mount will have to be used and I am waiting for someone to get one in stock. I would like some kind of mount that would set the OKO out a little further over the round, freefloating handguard - can anyone recommend one? I don't want to attach it to the HG... just extend it off the flat-top a couple of inches if that is possible to get it a little further out there.
As of that last trip to the range, I am still on the shoot 3, clean, repeat method, but the groups seem to have shrunk considerably. Probably more to do with the shooter than the gun, but I am looking forward to slapping a scope on it from the Colt or Armlite just for 100 yard groups. By what I have found so far, with no effort to find a load it likes (I have just used the same Winchester .223 fmj's through the whole process) I am sure it will be sub MOA with the OKO, if not the iron sights.
For anyone who may have interest in this equipment or the process, I will post another update after I finish the break-in and get some groups with a good scope and hopefully a little effort to find a load it likes best.