Very nice shooting from a very nice rifle there, Glenn.
I have another "1st" for the list. 1/2" Cooey 750

This was a fun little project that got into my mind because of this post in my thread about my Custom CZ 455
Well... I didn't exactly put a 24" straight 0.850" Lilja 3-groove barrel on a Cooey... But I did re-work an unsatisfactory Anschütz made barrel that I took off of my Weatherby XXII. Subsequently, said barrel was fitted to a Cooey 750 that I picked up off the EE. With less than 500 rounds down the tube so far, I am pleased with what I am seeing, and expect consistency to improve as the round count goes up. Nonetheless, after getting the barrel warmed up and lubed with SK Biathlon, I loaded up Lapua Polar Biathlon and nailed this challenge. Too bad for the danged "flier" on the last group, but the rifle does struggle to go 25 rounds without acting up at this point, something that should diminish with an increased round count. Didn't have to "get acquainted" with the rifle, or figure out some special hold for it... just applied my standard firm hold, held steady, and broke that 4.5# creepy @$$ trigger clean (like, the creepiest trigger EVER). Results speak for themselves.
Rifle: Cooey 750 w/Anschütz made Weatherby XXII barrel
Scope: Sightron SII 6-24x Fine Duplex
Rest: Caldwell Rock w/narrow front bag, Caldwell Rear Bag
Ammo: Lapua Polar Biathlon
Groups: 0.352", 0.303", 0.258", 0.359", 0.436"
Average: 0.338"
While I appreciate compliments towards my shooting... credit is more appropriately given to the workmanship on re-working/re-chambering/re-crowning/re-fitting the barrel and bedding of the rifle. To me, my shooting is neither here nor there... the rifle can either do this challenge, or it cannot, and if it cannot, it obviously has a mechanical issue with it. Sometimes these issues can be corrected, depending on what you are willing to put into the rifle

When I re-barreled my Weatherby XXII with another barrel that evaluated well, I quickly found success in this challenge. When I removed the flaws in the original barrel, I also found success in this challenge in less than 500 rounds shot with the barrel attached to a Cooey. Truly, rimfire accuracy is primarily based on the equipment one is using, judgement of weather conditions aside, as nobody should have much difficulty on this challenge off a suitable bench rest setup if their rifle is capable of the performance.