Anybody have one? Are they any good? Can they be rechambered to .223?

don't think it'd be worth it. but there's nothing wrong with the K hornet either. Loaded with a 40 gr bullet and 14.5 grains of lil gun you won't be far behind the 223

I was thinking more of being able to buy a 1000 rounds of Black Hills instead of loading those little bullets with my fat fingers.

It is not unusual to shoot 400 - 500 rounds a day on Ground squirrels.