I use to shoot the 50TNT's in my 222 - very accurate bullet.
I'm getting ready to try the 70TNT's in my 243win this year... will probably start off with IMR-4350. Will be trying the 70 Blitzkings, and more of the 70NBT's with this powder as well. Had tried the 70NBT's with Varget initially, then found a great load with them & Reloader 19, but that one was pretty mild... 3250fps. I want 'em 3500+.
In the 222, I used IMR-4198 (20.0 - 20.5), but in a 223... maybe Benchmark, or Reloader 10x? Benchmark is a great powder!