I've had only two Sigs, a 9mm P226 bought new in the late '80s and a new P220 .45 ACP bought about twenty years ago. Without getting them out of my safe to examine, I really don't know if they are all steel or alloy framed. Both have been fired considerably, almost exclusively with my own cast bullets.

I've had a number of 9mm and .45 ACP pistols and still have a few, but the Sigs remain more accurate than all the rest.