Re: Under an MOA but is it "GOOD"
You don't say if you're shooting from a rest (if so what kind) or what shooting positions you're using. That would help to better evaluate your shooting results.
First of all, your 600 yard target groups are just fine. I suspect you're still working out "shooter input" (rifle honeymoon) issues and when those are refined your 6" groups will tighten up.
Secondly, I'm impressed that you've learned to work with the scope turrets. While MV is certainly important, faster isn't always better. With the data you listed you're still well above sub-sonic velocities at 1k by a full 34%. At this point, I would focus on good marksmanship techniques and see if I could get it consistently at .5 - .75 MOA at 600 with the load you're using.
You've already learned that faster isn't necessarily better. Working for higher MV sometimes drives you into never-never land trying to find the next node and your rifle is unlikely to perform the same as the guy with an identical rifle using the same load.
I have a great woman, fantastic kids, a warm place to sleep and an accurate rifle. Life is good ..............
Hunter Safety Instructor - Rifle/Pistol Marksmanship Instructor - NRA Life Member
American rifleman's triad - God, guts and guns. It built America and it'll preserve America. Abandon one and you lose them all.