On several sub-forums I view the acronym "MIM" when discussing parts. While I anticipate this is some sort of manufacturing process, I have no idea what that might be OR how it differs in terms of quality, strength, or longevity when compare with drop forged or investment cast parts.

Anyone who is knowledgeable, please reply.

Metal injection molding.

check the FAQ section for an explaination......

FAQ's

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Ret. LE, FA Instr, S&W Armorer

I've always saw this as Made In Mexico - go figure

Garbage imo.

Thank you.

OP: run a search -- this has been discussed ad nauseum, is contentious and never ends well.

Back when MIM first came out (decades back) I researched it on line. I recommend doing that. In a nutshell:

1) MIM is metal injection molding. Steel powder is mixed with a binder (glue) and forced into a mold under pressure. The green part is then removed form the mold and "fired" which is like sintering. The part gets hot enough to burn out the glue and fuse the metal particles into a solid piece.

2) Gun makers have adopted it on every part possible because it's cheaper than machining a part, and (supposedly) it holds tolerance well enough that guns don't need to be fitted anymore during assembly...... which is to say they fired all the gunsmiths and let monkeys build the guns. You get to be the QA step.

3) MIM is not inherently evil, it is even used to make aircraft parts (although they X ray the parts to make sure there are no internal defects). But MIM is a stupid choice for parts that are long and thin or subject to stress when (as is the case with guns) there is basically zero QC applied to the MIM parts.

4) Most common defects are caused by: non uniform particle size leads to internal defect, air void (bubble) inside part.

MIM got a very bad reputation from a rash of failures of Colt 1911 extractors..... which is a dumb part to make out of MIM because it's long and thin. The thinner the part is, the higher the probability that an internal defect will cause a failure.

AFAIK, large parts like hammers and triggers have no MIM caused failures.

One decent reference on MIM:

An overview of the Metal Injection Moulding process

Many thanks for clear, cogent information.

As follow-ups, regarding "J" and "K" frame revolvers, please identify when S&W changed from drop forged parts to MIM.

Apparently, focusing on MIM parts in problem areas would be how to minimize reliability issues. If there is no clear demarcation for introduction of MIM parts, are there sources for drop forged parts to replace these "problem" parts?

I have 3 or 4 S&W revolvers that are newer, and use MIM parts. None have ever failed me in any way. These are shooters, that I trust my (and my family) personal safety with every single day.

That said, I have a handful of other S&W revolvers that I consider "collectible", and none of those have MIM parts.

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-Roger

I actually believe the "problem" MIM parts in your SW revo (if there are any) will reveal themselves in fairly short order. That is, if they are prone to fail they will. I have never been a believer in spending $$$ to "purge" a gun of MIM parts unless the part is somehow unsatisfactory. If it's a life defense gun I might reconsider, but my defense gun has all forged parts.

I honestly don't recall when SW switched to MIM, I thought it was late 90's (?)

I have some SW revos that have MIM and have tens of thousands of rounds fired and zero problems. I also bought a new PC 627 with "forged" parts mostly that had an MIM trigger strut which was defective. So, anyway, as far as I know there are no sources for "genuine forged parts" to replace all the MIM parts unless you get used parts. I believe the PC has also run out of forged parts too.

I find it a very interesting dichotomy when S&W 3rd gen pistol reliability is discussed in that forum section, words like "built like a tank", "stupid reliable" and other phrases implying solid "no worries" reliability are seen... when they have MIM parts too.

Whenever someone new to 3rd Gens asks about what spare parts to keep on hand for wear or breakage, the answer is almost always... " just springs, they're tanks". No mention of a need to keep a spare for the MIM hammer, or MIM trigger, or MIM disconnector, or ....

So why is it when MIM parts in revolvers are mentioned, it's an entirely different matter, and suddenly MIM becomes a seemingly fragile/unreliable and cursed part?

I'm not a MIM fanboy by any stretch of the imagination... just an observation having been a long time forum member that frequents both the modern revolver and 3rd gen pistol forum sections.

So far with the modern revolvers I've purchased within the past year (625-8 JM, 986 & 69), my main cause for complaint has been with inferior workmanship, rather than inferior parts performance.

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Conrad
SWCA #1830 SWHF #222