WTB: Glock 20 10mm to .357 Sig conversion barrel.  I know it's a long shot, but if you have one sitting around collecting dust, I'd love to take it off your hands.  Email is in my profile.

Perfectly normal.  Sigs have a rebounding hammer.  Part of their drop safe mechanism, the hammer is held off the firing pin so that if the pistol is dropped directly into the hammer it won't fire.  It won't be noticed in live fire.  The side-to-side play is normal too.