For those of you not familiar with the term, MIM stands for Metal Injection Molding if I'm not mistaken and please correct me if I am.
Here's an overview of what MIM is and how it is used in general.
I'm no expert on this process or the materials it produces, but more often than not these parts are winding up in our guns.Metal Injection Molding or MIM, also called Powder Injection Molding or PIM, is a net-shape process for producing solid metal parts that combines the design freedom of plastic injection molding with material properties near that of wrought metals. With its inherent design flexibility, MIM is capable of producing an almost limitless array of highly complex geometries in many different alloys ranging from stainless steels, alloy steels, and soft magnetic materials, controlled expansion materials (low CTE), and custom alloys. Design and economic limitations of traditional metalworking technologies, such as machining and casting, can be readily overcome by MIM.
Today, MIM is serving critical performance applications in a wide range of industries and products including, automotive, aerospace and defense, cellular telephones, dental instruments, electronic heat sinks and hermetic packages, electrical connector hardware, industrial tools, fiber optic connectors, fluid spray systems, hard disk drives, pharmaceutical devices, power hand-tools, surgical instruments, and sporting equipment.
I'll speak mainly to what I know about here, and in my experience I've had a firearm or two with MIM parts and I'm convinced they are not inherently flawed and that the material is as strong as anything.
What I don't like about it is that MIM is nothing more than a cost saving measure for a gun manufacturer; replace a couple of forged parts with MIM, keep prices the same, and save some $$$ for yourself. Smith and Wesson I'm looking at you.
IF there was any perceivable price benefit to the customer for the use of MIM and not just more profit for the manufacturer who thinks I'm not going to note the difference, I wouldn't be worried about it, but alas such is not the case.
Honestly my main beef with MIM on certain guns, Smith and Wesson revolvers in particular, is that MIM parts make an expensive and probably otherwise very posh firearm look cheap and shoddy. Case in point:
Now it looks okay by itself but compare it to this speciment with the forged parts. The 686 is the one closer to the bottom.
My photography may be crap, but you can see it for yourself sometime... hold a gun with forged parts against one with MIM parts and see which one looks like a $700 MSRP firearm.
I realize what it looks like doesn't impact how well it works, but when I'm shelling out that kind of $$$ I expect a certain level of "fit and finish", including a little more attention to details like that.
I wish forged parts could at least be had for those of us that care for them or that manufacturers would at least hard chrome the MIM parts that are visible. My 625JM for instance is a great compromise... sure it's got MIM parts but they don't look like it.
On a gun I buy for economy MIM parts are just fine, on a gun I buy because I want the best of its kind available, the MIM parts bug me.