Swifty,
I've put close to 3K of cast SWCs through my 220ST without a hitch. I believe that SIG also advises against reloads, so it might be a liability thing. Mine feeds the SWCs very, very reliably, I'd say more so than my Colt 1911. The only problem is that my SIG seems to lead some. I run a couple of mags of JHPs through it after every practice session, and it cleans up nicely after that.
My 220ST has quickly become my favorite handgun.
Chuck