Lots of options and possibilities out there, that is for sure.
If you want to keep the option open to ever shoot factory ammo, 22-250 and 22 Creedmoor will be your best options. There's always the 220 Swift, but brass quality is much better for the other two.
One of my all time favorites is the 6-284. Even though the 6-284 is technically a "wildcat" cartridge, it's so easy to make and load for I barely consider it one. My 6-284 was the first gun I ever had built and I can't imagine ever not having one in the stable.
The 6 Creedmoor is basicly a 243 but IMO with a little better case design. I'm getting ready to have a 20in. 6 CM built to shoot 70gr Ballistic Tips as kind of a mid range shorty build.
For a hot rod 22 cal build maybe talk to Defensive Edge Rifles about their 224 Terminator, it's their version of a 22-243 Improved. One of the big benefits of going with Defensive Edge is you can buy "formed" Lapua brass ready to go right from them so you won't have to mess with fireforming yourself and go straight to shooting.
I'm shooting the 80gr ELD-M at 3650fps from my 224 Terminator and the thing shoots like a lazer. With only a hand full of rounds down the pipe, this was the first group Shawn shot with it.
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