I've got a Criterion 6.5CM also, in a Howa 1500 with Bighorn barrel nut system (Remage for Howas). It shot a bit iffy to start - like .75-1.25moa. I took it apart, torqued nut again and let it shoot itself in a bit. After about 80-100 rounds it came right in to 1/2 moa.
Personally, I've not had much luck with Satterlee method; statistics being what they are, its possible to get a flat spot in the wrong node (i.e. good SD/ES but bad precision) and Chase your tail trying to improve groups.
I have much better luck with a 4 round OCW test starting at .010 off lands for VLDs or .020 off lands for Secant/hybrid ogives. I typcally shoot them at .3gr intervals in a flat row with a level line drawn across the target. This helps identify the "high point" and "low point" of barrel harmonics. Like this:
In this example, I already knew ~42gr was the node but wanted to confirm with .1gr test. First two VLD group was shot at wrong paster so I just marked accordingly and transposed group with sharpie.
Notice the group center at 41.8, 42, 42.1 and 42.2 are all similar L/R and U/D. 42.4 shifts left and down. That was shot with about 100rounds down barrel; it has tightened up considerably since with same load (and very limited cleaning).
With the SMK, while 43.5 shot SUPER well in that group, it was not repeatable (at least not .17" repeatable). It shot about .5" in subsequent test of same load but the SD/ES weren't all that great around 16/30+. But it was still in the best node for that bullet test. The barrel was at it's bottom point so it shot pretty well.
Here is how it has progressed since with 140VLDs at 42gr H4350.
150 rounds in no cleaning since 100 rounds:
200 rounds in no cleaning since 100 rounds:
Not sure if this helps but I have a 1-8T 26". Here are my loads with 5 shot groups:
- 140VLD Hunt at -.007 from lands (2.892" oal) 42gr H4350 Hornady brass, CCI BR2 primers .3-.4 MOA 5 shot and .6-.7 10 shots 2770fps/SD 8-10
- 140 VLD Target - same as above - .2-.4MOA 5shot groups 2770fps/8-10SD
- 140 Hornady ELDM Cloned Factory - 2.812" oal , 42gr H4350 CCI BR2 primers Hornady brass 2760 FPS SD 10-12
- 140 ELD Factory shoots .4-.6" at 100yds 5 shot groups around 2730fps SD 7-15 depending on lot#.
- 123 SMK -.020 lands, 43.5gr H4350, Hornady brass, CCI BR2 ~.5-.7"
My suggestion is if it's not shooting factory ammo (specifically 140 ELD Match) at or better than .75MOA for 5 shot groups, you should talk to Smith and/or Criterion. They have been great to work with so far and super willing to help. Could just be a bad barrel if you've tried all other options.
Good luck and keep us posted!