What's the scoop about MIM(?) parts on Smiths?

[toolmaker]

If I remember right, MIM stands for "molten injected metal". Please educate me. Is this correct? If so, what are the ups and downs? As a toolmaker, I'm familiar with powdered steel approaches and castings. Are these parts still n Smiths? Thanks.

 

[dfariswheel]

MIM stands for "Metal Injection Moulding".

Many internal S&W parts are now MIM including the hammer and trigger.

Basically, powdered metal is mixed with a plasticizer and injected into a mould.
When heated the plasticizer melts, the metal melts and then shrinks slightly as the metal cools.
The mould is opened and a virtually finished part is removed.
All that's needed to finish is to case harden the part so it will wear properly.

The up side is this allows the price of the gun to be held down.
Very intricate parts can be made much cheaper, and this allows doing things that normally would significantly add to the price of a gun.

The down side is, the parts just don't seem to be as strong as forged and milled parts.
A good number of people have experienced broken MIM parts, and NOT just from S&W.
Remington used MIM extractors on their 870 Express shotguns, and apparently had breakage problems.
Remington MAY have discontinued the use of MIM extractors.
The latest guns seem to have milled extractors. (NOT 100% sure about this).

Although the industry states that MIM parts are very near to forged parts strength-wise and for longevity, "real world" experience seems to indicate otherwise.

Another down side is, public perception.
People just don't like the idea of MIM parts, even in those applications where the part is as good as a more expensive forged part.

Whether we like MIM or not, we'll be seeing a lot more of it in the future, but the bright side is, it's use will help prevent the ballooning of the price of a gun.

 

[Jim K]

MIM parts seem to stand up pretty well to pounding, but can fail under a bending stress, as in the barrel bushing skirt on a 1911 type pistol. MIM is totally unsuitable for some parts, such as 1911 type extractors, which must be made of spring steel.

I have heard of S&W MIM revolver parts failing, but only on the net. I have never seen a case or been told of one by a gunsmith or by the actual owner of the gun. One reason I have been skeptical is that I think if anyone can do MIM right it should be S&W. The other is that reports of S&W parts failure are almost always by folks ranting and raving about S&W's "deal" with the Clinton administration. One such claimed that 90% of S&W hammers and triggers broke, an obvious lie.

BTW, for anyone interested, S&W hammers and triggers have not been forged for nearly a century; prior to MIM, they were punched out of steel plate.

Jim

 

[mec]

I've put several thousand rounds though a 617 MIM without any signs of wear or any parts problems. Of course a .22 isn't the same as a magnum revolver.

 

[RON in PA]

Smith and Wesson claims that one reason for MIM parts in their guns (esp. triggers and hammers) is reliability. This makes offering their lifetime warranty financially feasable. Also parts variability is reduced so that there is better interchangeability of parts, less hand fitting. This reduces the time necessary to put a gun together. It's the bottom line, but also maybe a better product, even if it's not as pretty.

 

[New_geezer]

As a relative newbee, I don't know how long MIM parts have been around. But I'm guessing there's a learning curve involved in perfecting and controling the process and once a company has that down there will be few problems. As has been suggested, it seems the process imparts certain qualities into the metal that make it quite suitable for some applications and not others. These qualities would be related to both the process itself and the type of metal being used. On the surface it seems like the MIM process would have several potential points of failure especially if the company was slack about QC in materials and procedures. On the other hand if done right it sounds like it could solve certain production problems as well as making some innovative design decisons possible. Perhaps someone with some metalurgy experience could elaborate.

 

[Majic]

S&W may claim that in public, but the bottom line is MIM parts are cheaper. Variablity in tolerances were drastically reduced with CNC machines. There has never been a problem with the parts reliability (except with the short usage of stainless steel parts). Many owners and gunsmiths what swapped out hammers and triggers without much if any fitting. Most stoning have been done to improve the action.
The bottom line is the MIM parts are cheaper and a profit driven company will explore all options to increase profit as long as they deem the product doesn't suffer.

 

[RickH]

I just called S&W today for a return tag for my mod.60 .357. A piece broke and fell out of my gun. It appears from the schematic in the manual (a general revolver schematic that obviously isn't a j-frame)to be part of the hammer block. I don't know if it is mim or not, but it sure is broken.