Can I replace my 308 Win barrel on my Rem 700 Short action with a 300 Rem Ultra Mag barrel and not do any thing else for it to work?Or will I need to change out the bolt or mag.Thanks in advance.

What is the final chambering you are after? The .308 win has a .473" bolt head, the 300 UM is .532" at the head. The .308 is 2.0" long, UM is 2.85" long.

If you are looking at a single shot, the bolt and extractor could be opened up. For a repeater, you'll need to start with a long action.

Thanks Paul