The used one will work fine,but the new one gives you more ability to make sure your forearm stock will fit tight because of the unwelded clevis" or mounting bracket" Used one could be dented or have pitting and possibly a bad sleeve as the guy above said.. I got a used one in mint condition from HKparts a year ago,it worked nice on a ghillie build. Its really more about the exp. of the builder. This is a tricky area to weld without burning thru and ruining it. If done wrong,you could end up with NO cocking handle gap or not enough. Goodluck bro.