Steve123, You're correct (not enough coffee first thing in the morning). My post should read "which the .204 Ruger was based on, via the 222Rem Mag, also the basis of the 17 Rem."
The 17 Rem is not based on the .223, though it can be used in a pinch, albeit with a short(er) neck.
Agreed as well on the .20 Practical/Tactical for launching heavier bullets at high speeds. I had a 20 Tac made not long have Todd K and (I forget the other gentleman's name) published an article in Shooting Times. Back then Douglas was the only game in town for barrels, and bullets were pretty scarce (Berger and Hornady were it IIRC). Anything else was a completely (garage shop) custom bullets route. That 20 Tactical of mine is/was a killer in the PD towns.
I also have a 17 AH, built on a Browning Micro Medallion by Greg Tannel(sp?). Sweet little rig, and about as perfect as you can get for a fox hunting, fur friendly rifle. Plus, its a Browning, so the wood on that rifle is a sight to behold. I have a 17 Mach IV as well, though it is a tight necked version (not what I ordered, but what was delivered), that is also insanely accurate, but a PITA to load for. She doesn't get shot much.
I've got a buddy that shoots a .20 Vartarg, and with LC formed brass, gets insane velocities; well over published data. The guy was dinging stuff out to 600yds with that little bugger. Definitely raised a few eyebrows over at Saubiers.com. The Vartarg is where the toughness of LC brass really stands out.
I've been messing around with "sub-calibers" since the late 90's, and its been interesting seeing the growth in popularity and support by the industry (not unlike the LR game of late).
BTW, H-322 is about perfect for the 20 Practical/Tactical as powder.