what kind of performance are you looking for? ive built a few 6mm wildcats, and i ended up getting rid of all of them other then my 6mm mongoose. i can get a 90 grain eldx to 2850 fps out of my 20" barrel
it uses mil surplus 5.56 brass, and isnt hard to load for (very accurate with most loads ive tried) so its standard mil spec parts/magazines, just a barrel swap.