Finally got around to getting my Ruger American set up and want to purchase a couple different types of ammo to run through it.

I’m looking at the FGMM in 130 & 140 grain, Hornady Match EL-D in 120 & 140 and Winchester Match 140 grain. I know I’ll get the answer after a range trip but for those of you who own this rifle or similar: what are you finding is most accurate, 120’s or 140’s?

 I can't speak for Ruger
6.5 CM 20" barrels in 1:8 twist, but my 20" Aero Precision chambered in 6.5CM with 1:8 twist performs exceptionally well with 147gr. Hornady Match ELD ever so slightly over 140 gr. Match ELD.

Both shoot sub 1/2" inch groups with the 147 shooting +/- .25" groups at 100 yds and the 140gr in just under .5" groups.

130gr. FGMM shoots around .75" groups in that same barrel.

Not too shabby! @charliedontsurf

Of course, YMMV, just my experience in another brands' barrel in the same caliber, barrel length, and twist rate shot with factory Match loads.

I'd skip the 120 eld-m. Your rifle has a 1:8 twist. Take advantage of that and try 147 eld-m instead. The 120 eld-m has the lowest BC of all the rounds mentioned and even though it'll be faster at the muzzle, it will actually be slower starting around 600 yards. It will also require more windage adjustment than the heavier rounds.