RL16 will do it easily, 43.5 gr gets me ~2,830 fps with 127gr LRX out of a 20". The Alliant website gives a max load for the 129gr SST of 44.4gr @ ~2,949 fps.
As antelope_sniper said though, lots of powders (especially 4350 burn rate and slower) should give good velocities with that bullet. I like the 129gr IL in my Grendel because it doesn't protrude into the powder column very much so you can load it up with slower or bulkier powders.
I will say that in my 22" Montana, the 129gr whitetail chrono'd at ~2,760 fps, not quite box velocity.
Last edited by Gtscotty; 07/12/20.
