Re: boltface options on 7mm sendero
A good smith can open it up and make it sized for the RUM's or even the 338 Lapua. Some smiths will open them for the Lapua and some wont. A really good smith can machine a ring and fuse it into the face for a standard 30-06 case also. Whether it gets bigger or smaller, it will require a sako style extractor. Otherwise you are stuck with a standard magnum. Ie: 300 winnie, 7mm Rem, 7 STW, 338 winnie ect...
It is typically better to start smaller and go bigger and not the other way around despite the fact that it can be done.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.