10mm ammo and 30-06 is a lot harder to find ammo for than .45 ACP and .308/7.62 NATO.
My primary "Oh ****" arm right now is my Saiga 12ga magfed semiauto (gas operated). They're cheap and reliable.
Winnie Defender w/ the short bbl here, light collector up front. It's a pump but my Marine buddy came up with a bandolier of incendiary, AP (yes and yes), tracer, and other assorted loads for it.
Also, I inherited a 9mm, the 10 was for those who already have them.
I do believe I destroyed all that exotic 12 ga. ammo when the Fed's illegalized it... truly a shame.
;-)