I'm no expert, just an extensive user.
Frank is right, durn little activity with a neat little cartridge. Wes
Ugalde designed the TC
U cartridges to utilize the 223 Rem case and expand their capacity by employing P. O. Ackley's shoulder design. Should be able to top 6x45 velocities just a tad.
Bob Milek worked with DuPont to develop loads and came away with some great results. Among them, using a 6.5 TCU barrel only 14" long and a 85 gr. bullet with IMR 4198 averaged 2525 FPS with functioning pressures only at 49,300 CUP. As fas as TCU chambers go 7mm is mainstream and 257 is the unicorn. My favorite is the 6 TCU. I've got a 16.125 " barrel for the contender that is a real shooter but I have a 6x223 14" that is a lot of fun off the bench too.
I would think that your AR barrel, being at least 16", could really surprise you with a TCU cartridge.
I have no idea what it would take to make that change.
I know, the path less traveled ...
I built my AR to accomodate the 6.5 Grendel only because it was gettting popular at the time and I have a contender barrel in it.
They both shoot excellent, but I prefer the contender because I abhor movement after trigger pull short of game falling down.
I'm done with my rant,I'll let others chime in.
Just for giggles, compare the 7 Raptor ballistics to the 7TCU ...
Here's a little of my woodwork on a contender with a 10" 30 Herrett barrel that's been threaded and pinned with a 7" vented extension