The P220, P225, P226, P228 and P245 are or was all folded carbon steel. The P226, P229, P239 and the new P220 are milled(forged) stainless steel. I happen to like the folded steel slides but the P229 is my favorite. SiGARMS is going all steel slides. Sounds like a economic decision and like stated earlier the newer P226, P229 and P239 were created for the high pressure .40SW and .357SIG rounds. There are still a bunch of stamped slides available everywhere. CPOs are one approach and buying via the classifieds on Sigforum, Glocktalk and Calgins.net are another. I've purchased a P220, P225 and a P245 in the last 3 months with no issue. P228s are getting harder to find because they're popular but they are still abundant. In any composition be it stamped slide/aluminum frame, milled slide/aluminum frame or stainess slide and frame, they're all nice weapons.