Kimber's predominantly MIM parts are reknown for breaking. And how disheartening it is to have a thumb safety, mag catch, etc. snap off in your hand!!! I've seen a Kimber MIM thumb safety snap in half on a new Kimber in a gunshop. Yikes. MIM has a nasty reputation for snapping in two just when you least expect it.
While McCormick parts generally have a good rep, I believe most of them are MIM as are most of the Kimber parts. I'm not so sure that some of Wilson parts will be much better, but I believe Wilson is no longer buying MIM process parts for some of their premium parts. Many MIM parts can and do work fine... but I don't tend to have a lot of trust in them.
I'd suggest going for premium forged and cast parts: Ed Brown, Cylinder & Slide, possibly STI and Caspian as well. Look for forged tool steel where possible.
Don't want to start a MIM debate here because there are some folks who think MIM is just dandy!!! The funny thing is, companies and people don't choose MIM as a manufacturing method for parts because it is a superior product (it's not)... they choose MIM because parts can be made more cheaply with that manufacturing method. It's about saving money, not producing superior parts. Superior quality parts costs more money, pure and simple. I believe on a defense handgun, cheaper parts is false economy... I'm happy to pay more for the best parts in a 1911. If you're willing to pay more, you can get better parts. If you want to go "on the cheap", expect to pay a price somewhere else (in reliability, durability, quality or performance.)
Most MIM parts probably work fine (if they're well made). Problem with MIM is that you have no idea how "well" the MIM parts are well made unless and until one snaps in two when you might need it most! For me, I just prefer to avoid MIM when possible, though that can be difficult to do without effort and expense. Other's opinions will vary.
