It has the same problem that all the wildcat cartridges based on the 5.56 case have. Limited powder capacity. You'll be better off with a 6.8 SPC or a 6.5 Gendel. They use larger cases and have 50% more powder capacity.
I've had a 7mm TCU in a Thompson Contender back in the 80's and its a 100-150 yard deer cartridge. Its not that it can't shoot farther than that but it lacks the energy t get the job done beyond those ranges. You'll be lucky to drive a 90-100 grain 6mm bullet more than 2200 fps in a 6mm TCU (its only got enough room in the case for about 20 grains of powder). While you can get 55-60 grain 6mm bullets what's the point? You can do the same thing in a 5.56 and with the 6mm you gain .44mm in bullet size. Big whoop. The .300 Blackout suffers from the same problems in terms of case capacity.
The 6.8 SPC is about the optimum for case capacity, velocity and bullet weight in an AR platform.
The erstwhile negative side to the 6.8 is you need a different $60 bolt and different magazines. OK...I can live with that. Its not like I built my 6.8 guns for high volume self defense practice and SHTF. They are hunting guns. 3 or 4 dedicated 6.8 mags and a bolt head cost about the same as 200 rounds of 6.8 ammo. If you can't afford those upgrades you probably can't afford to shoot the gun to begin with.
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