MIM. It's a controversial topic in the gun world; mostly because manufacturers have been replacing formerly cast or forged and machined components, with MIM parts that have been surface hardened and/or hard chromed.
If it's done right, MIM parts should last as long as any other metal bits; and be cheaper to boot. Of course if it isn't done right, you wont know until the part suddnely fails, and you get a "crunch" instead of a bang.
Another issue with MIM, is the surface hardening. It makes the parts difficult to machine; and if you have to significantly reshape the part you'll cut through the hardening, exposing the soft metal underneath. This softer metal will then wear differently than the hardened surface did, and stress risers will devlop at the interface between the hard and soft surfaces; which will induce cracking.
Overall, I simply prefer not to have MIM parts in any load or stress bearing capacity in my guns.
The first thing I did when I got my Springer, was replace all the internals with tool steel or titanium parts.
Do I expect the MIM parts to fail? No, not really, but they weren't the best quality parts to begin with, the new parts are better, and more suited to what I want; and really given the fact that this gun protects my life on a daily basis, it’s more than worth it.
I got a deal on the springer at $800, and I bought it specifically to be a custom carry gun, with Yost in mind for the internal parts, so it's not like I was suprised with a big bill for an unreliable gun. The gun operated just fine with the original parts, I just wanted better ones.
On a Springer you want to replace the following (the list on a Kimber is similar):
7. Firing pin (sometimes. Some Springers have titanium pins)
8. Firing pin stop
9. Magazine release
Strictly speaking replacing the trigger isn’t necessary, because the stressed and wear part of the trigger is the bow, which is cold rolled pressed sheet anyway; but I replaced my trigger with an ultra short, ultra light Ed Brown serrated trigger; just because I like an ultra short trigger.
The only MIM part I didnt replace was the beavertail; one, because it isn’t a stressed part and is incredibly unlikely to break; but also because replacing the beavertail with someone elses model may make the gun LESS reliable. Beavertails are supposed to be interchangeable, but in reality they require an awful lot of hand fitting if they are going to be close fitted and still be reliable. The factory piece is well finished, and well fitted, so I didn’t want to mess with it. I DID chamfer and smoothe the edges of the hammer cutout, and the top surface of the part though.
I replaced all the ignition components with Yost (and had him fit them. He’s only 15 minutes from my house - 'course he took three months to do it); and the hard parts with Wilson or Ed Brown machined tool steel pieces. I also replaced all the springs with Wolff; and that stupid springer ILS with a Smith and Alexander arched mainspring housing with integrated magwell (that I blended with the frame).
The entire cost to replace those parts with top quality Wilson, Baer, Brown, Yost etc… parts is about $300; but you can get good forged and machined parts for as little as $150 (without the Wolff springs or the magwell of course).
Why didn’t I replace the barrel? Up until recently (some time last year), Champion barrels were Nowlin match bull barrels without the final surface finishing. Oh, and the factory sights are Novak LowMount combat tritiums, which are already about the best.
Essentially, my Springfield Champion, is actually a Yost Custom Commander, built on a Springfield frame and slide; and it's exactly what I want from a conventional framed 1911.