No restrictions in NZ regarding 18" barrels, I could go down to 16" if I wanted. We have an overall firearm minimum length of 762mm, but no specific barrel length regs. Maximum mag capacity is 7 rounds (before you need a special licence and 6mm thick walls on gunsafe). So my next mission is to cut the follower back on my five shot mags so they can hold seven rounds. Ah yes, the magic number of "7"!!