1/4" groups with a rimfire are a certifiable challenge, good sir. I shoot many with my custom CZ 455, but 5 in a row still hasn't happened. To your end, I'd say grab the brick of SK, more shooting and it looks like it'll do 1/2" for ya. The thing about "better" ammo, is that it often doesn't shoot any better in a particular rifle just because it is more expensive. I've had Eley Tenex with an ES of 7 FPS for a 5-shot group flip out to the 0.9's, all because of disagreeable barrel harmonics. Run it through a different rifle that's tuned, and it comes dang close to that 1/4" goal

What I see in your targets is likely a good barrel that just needs some tuning. Try a bunch of ammo and something will stick, or a little tuning with SK and you're blasting 1/2" all day. Oh, and if you ain't cleaning, you ain't winning