This is a semi auto tube for the STERLING MK4. The builder can make a receiver out of the tube, it has a template to assist in drilling, venting holes already drilled. The end of the tube has been bored out to accept an original front barrel bushing. The tube has a reduced inside diameter and will NOT accept a full auto bolt. A milling machine or dremmel tool is required to finish the tube. 

Due to demand, Sterling tubes are limited to one per customer per 6 months until noted otherwise. Thank you.