tldr: If you're shooting at extended ranges (200+ yards) - try one of the long-range variants - Lapua Long Range or Super Long Range, or SK Long Range Match. A lesser-known and not-easily-found option that did well for me was RWS R100.
I've tried three different lots of Lapua Long Range and all have done well. I tried one lot of Super Long Range - just 10 rounds exchanged with a guy I met at the range - and it did not impress at all (same lube is used on all SK/Lapua SKUs except Polar Biathlon Extreme so switching among different ones has little to no accuracy effect, especially after 3-5 rounds fired).
Rimfire ammo is a lottery.
------
The arrival of Lapua Long Range and Super Long Range on the scene muddied the testing waters - because the Lapua testing centers won't test it (they only offer testing with Center-X / Midas+ / X-Act) and they only go to 100 meters anyway.
@grauhanen described why any random lot of C-X MAY outperform a lot of Midas+ or X-Act - and, with the SK SKUs being produced on different machines in the same factory and presumably graded using the same or similar process, a lot of Standard+ might outperform any of the Lapua SKUs. Not likely but possible.
It really is a lottery.
-------
With that said - I sent my gen-1 Vudoo in for testing just as the pandemic hit in 2020, requesting tests with Center-X and Midas+. At the end of it all,
in my rifle, the best lot of M+ outperformed the best lot of C-X at 100 meters - but only by 4mm, and there was plenty of overlap across the various test groups. So I bought two cases of Center-X, at a cost of 40% less then M+. That ammo has performed well in every rifle in which it's been tried, at ranges out to 400 yards.
And, interestingly, a buddy of mine bought two cases of M+ after testing at about the same time. He and I have gone head to head for a few years at a little gallery-style match we enjoy and, with both of us shooting near-identical gen-1 Vudoos out to 150 yards, who prevails on any given day comes down to who lucks out with wind. Another competitor with an Anschutz 54 shoots nothing but X-Act. He's always in it out to 100 yards but generally is behind us at 150, probably because buddy and I shoot a lot more PRS-style rimfire matches out to much greater range - not because of rifle/ammo capability. And
@Rob01 plays in that match too, running SK Long Range Match, and, again, any given day's result comes down to the fickle finger of wind or whatever.
---------
OP, if you're budget-constrained, you might consider a tuner. This statement may open the door to the pissing and whining over whether a tuner works or not. I don't care. My experience with tuners on four different rifles wearing barrels from moderate "kukri" contour to near-straight-taper Heavy Varmint was that three of the four showed definite "impact" on grouping; the 4th was one I messed with early on and my lack of experience may have been in play. A tuner will not transmogrify crappy ammo into good ammo, but it might help mitigate lot-to-lot variation among lots of good ammo.
