Woops I jacked up my barrel

[woohoo]

Thanks for that.

I have been looking at putting an on-board air compressor on my SUV for airing and changing tires, including using an impact wrench. I can imagine the expression on my wife and kids' faces if I ran the 30' hose into the office workbench.

Would I be nuts to start by building a .300 WSM AR?
Or should I plan on my first project being a throw-away?

There are a few problems with magnums in the AR10. The mags don't feed well even if you can find a RSAUM follower. The extractors are made for 308 sized cases. When the extractor moves out far enough to snap over a .535 rim it slams into the lugs of the barrel extension. If you modify the extractor to work it will be weak and break off.
You could clearance the 2 barrel extension lugs where the extractor slides through but you still need a RSAUM bolt that no one makes and the mags still don't work.
Save yourself a bunch of headaches and do something else.