For some reason I was thinking the S&W was Zinc. Is the M&P made by Umarex? I was under the impression than Umarex made the 22lrs for S&W and Walther.
The M&P-22 (like the "Walther" P22) is made by Umarex. The slide is made of a zinc alloy that sometimes goes by the trade name "Zamak," which is commonly known as potmetal. This is a lower-quality material than the aluminum used by some other pistols like the Ruger SR22 or Browning 1911-22.