There are certain components in a 1911 that should not be made of MIM but my experience with a couple of quality 1911's that contain MIM, and tens of thousands of rounds through them, MIM has not been an issue.
Mjolnir has a point about design. There are certain parameters that should be considered when using MIM in production. I would not want to use MIM on a component that flexes, like a 1911 extractor.
Rumor had it that Glock has been using MIM components for many years but I never researched it to confirm and never really cared since my experience with quality MIM parts has been excellent.
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