As an FYI sig has announced a recall related to a hammer issue see attached for related info to verify if you have rifle afffected by this recall.                                               

Hello NLEFIA members, Sig Sauer has issued a safety warning and recall notice on select Sig rifles. Click on the link for more information... https://www.sigsauer.com/press-releases/sig-sauer-safety-warning-recall-notice/ Fortunately I checked the one I have and it was not involved in this issue

yeah some supplier screwed up. If you bought an M&P branded lower parts kit of the right vintage, they have a recall too for hammers with improper heat treatment. 

 

http://www.thetruthaboutguns.com/2017/09/daniel-zimmerman/battenfield-technologies-recalls-mp-ar-15-complete-lower-parts-kits/