243 powder?

[Starlite]

I wanna try some N555 with a 105/108 and see what comes from that

Is that their new powder?

 

[RH300UM]

Is that their new powder?

Yep
On par with RL16 burn rate. I would like to try it in a few case/cartridges

 

[Dosh]

The OP could spend thousands trying all the suggested powders if he could find them.

 

[freefloater59]

45 gr IMR-4831 with 100 gr Hornady, DRT at all ranges.

 

[Black Hat]

My favorite powder was vhit n560 but that is like rocking horse excrement here in Aus, so now I load 41.3 grains of AR2209/H4350, cci br2, lapua brass, Berger 95vld.

10 shots 1 hole 100m, can't complain.