I would suggest at first to make it uncommon (i would assume it is ment this way because of the high cost).
And i would appreciate a cap, 30 is quite low, maybe 48 (Dmg ratio: 1:1,5)
Edit: Oh, i see now that it is durable, ok, then 30-35 is quite well
Edit 2: Oh man, my mathematical skills are quite low today... 23/2 is 11,5, not 16 ;)