Sounds like the case isn't expanding evenly and enough around the case mouth upon firing to seal the chamber completely. Since the 220 is made primarily as a self defense sidearm, reliability is paramount over all else. To make sure the round chambers each time, even when dirty, the chamber was made a little large, yet within specs (In all honesty, I haven't checked this, but believe it to be true, since its a Sig.) The burned powder/carbon fouling is leaking back around the case turning the side of the brass black. This is common on many self defense gun and shouldn't be an issue unless the ammo is inaccurate. If that's the case, (no pun intended), then use whatever you like best and shoots consistant groups.
Just my .02c. Hey! Why are you giving back change?!?!
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"But now, he that hath a purse, let him take it, and likewise his scrip; and he that hath no sword, let him sell his garment, and buy one." -Jesus Christ (Luke 22:36, see John 3:15-18)
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"Reasonable gun law?............There's No such critter!" --EQ
