I have built a couple of the Stevens 200's, same bolthead, etc...so it was just screwing on a new tube...but i bought a pre accu trigger 116 in 270 cal, and i want to go from 270 to 7 mag, or possibly 7stw.....what other than the bolt head will need to be changed? And if the mag, can i buy the Magnum magazine? Thanks, rsbhunter