New guys,
Here's another welcome to the Rohrbaugh forum. Lots of good information and good people here!
I, too, have fired 115, 124 and 147 grain ammo from my R9s (very early build, but with updated recoil and mag springs.)
Basically, I stick with the 124 and 115 grain ammo - preferably in Speer GDHP. Main reason is I feel the R9 barrel length is pretty short to stabilize the longer, heavier 147 grain load. I actually measured the rifling twist in my barrel, ran the Greenhill formula (from the NRA Firearms Fact Book), and found the 147 grain bullet should stabilize IF the barrel were long enough to spin the projectile up!
Otherwise, I agree with Richard: A big heavy rock does more damage than a little rock.
Steve