Wow, the Model 70 extreme weather in SS is extremely dito find.
Now that I’m looking for one, these are extremely hard to find. It says that they have discontinued the SS version.
It’s now the Extreme Weather SS MB, it comes threaded and with a muzzlebrake. You’re probably seeing the old unthreaded version that has been discontinued.
I picked mine up from Bass Pro they were actually a couple hundred bucks cheaper than my LGS, I think they have went up a little since then. I prefer the tan stock from BP but it looks like they only carry 300WM and 6.5CM.