Will be recieving a 6tcu 21" barrel soon and wanted to hear what your favorite powders and bullet combo's are.

Congrats on acquiring a superb caliebr.

Start with H335, and you will look no further for a propellant.

I've poured quite a bit of it into various 6mm TCUs and 6mm-.223s (6x45) and have always been rewarded with stellar results. Since the discontinuation of the Sierra 80 grain SSP, the 80 grain Ballistic Tip and 80 grain Speer have proven their worth, particularly with the somewhat higher attendant velocity of a carbine barrel. (Most of my shooting with the smaller 6mms has been for coyotes and smaller deer.)

Start at 24 grains and work up in half-grain increments. You'll more than likely find the sweet spot somewhere between 26 and 27 grains.

Also, I prefer Rem 7 1/2s.

For lightweight projectiles, H335 will do fine as well, but BenchMark and H322 will give you a bit more speed with 70 grain and under bullets.

I would add TAC and RL10X to what Bobby told you. I have tried many different powders with 55-70 gr bullets but the standouts have been H335, TAC and RL10X, my barrel has a 1/12"twist so I Haven't tried any heavier bullets.