Bought a J&T bull upper w/ 1-8" twist bbl.  just wondering what the ideal bullet weight would be for it.  I have a bunch of Hornady 60gr. HPs, and Sierra 69gr HPBTs as well.  Also, would like to know what is the lightest bullet one could use in it as well?  TIA

anything from 50-80g should be ok to shoot.  The ideal bullet is a 75 or 77 grainer IMO.  They generally give excellent results in barrels with a 1/8 twist, and they do for me in my AR with the same twist.  I haven't tried the 69 SMK, but I've heard good things about them in the reloading forum.

If you are rolling your own, try RE-15 or Varget behind heavier bullets.  They are excellent powders and aren't temperature sensitive at all.  Perfect for 75/77g bullets.

the best i've run in my 1:8 barrels is blackhills 68gr hollowpoint. the 75 gr hornady did not work well for me. 55gr does OK. forget the 45 gr stuff. way too light.