After thousands of rounds barrel replacement is recommended. This replacement barrel will renew your SMG or MPA semi auto gun. Easy installation takes only a few minutes, make sure to remove the barrel pin before unscrewing the barrel and use a barrel wrench or one of our McWrenches. Pleas.45 acp Barrels are in short supply at this timee contact us if you have any questions. Barrel thread is 7/8x9.