WSM actions aren't hard to find. I had no trouble getting my 12 VLP DBM. In fact, that model has about everything you said you were looking for without having to build it. Unless the barrel on that model is a little too big for what you're looking for. It's large shank, detachable magazine, laminate stock, heavy barrel. And it's made in 300 WSM as one of the cartridges. And yes you can use a small shank for the WSM but some of us prefer the extra meat the large shank provides. I just feel better about it. Good luck with you search.