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S&W pre-MIM

asphalt cowboy
A friend was asking me about one he had seen on the auction side.

What's the MIM stand for?
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7 comments

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  • beantownshootah
    MIM = Metal injection molding.

    It refers to a process that uses a polymer binder to help hold metal particles together. The molded polymer and particles are heated, and the polymer melts/burns away while the particles fuse together to create the final part.

    The point is, its a cheaper way to make certain parts than traditional forgings.

    Even though MIM parts can be made to high tolerances (higher in fact than most ordinary production techniques), and if done correctly should be extremely strong, purists (and internet-wannabes) dislike parts made this way, preferring the old-fashioned forgings, etc.

    EDIT: "Pre-MIM" refers to older Smith and Wesson guns that were built before Smith starting using MIM parts (in the late-90s, IIRC).

    Note that not EVERY part in modern Smith guns is made with MIM, just certain ones.

    Also its not JUST the MIM (or lack of MIM) that's a difference between the modern and older Smith revolvers. Older guns had pinned screw-in barrels that were potentially replaceable. Current guns have crush-fit barrels that are not easy to replace. Older guns all used forged solid steel barrels. Some of the current gun use barrels with a rifled steel liner instead. Older guns may have been tuned by hand by seasoned gunsmiths as a matter of course before leaving the factory. Current guns, not unless they've been through the Smith Performance Center. . .because the high consistency of MIM parts makes hand-fitting of parts less necessary. Older guns had no lock, but current guns have a lock behind the cylinder release that lots of shooters hate.

    So there are multiple reasons why the older guns could be considered higher quality.
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  • Hawk Carse
    Metal Injection Molding.
    Very fine metal powder is in a plastic carrier and can be injection molded like straight plastic. The molded "green" part is then heated hot enough to burn off the plastic carrier and fuse the metal powder into a near solid state. Claimed to be 98% the density of bar stock.

    Advantages include speed of production, making shapes difficult to machine, and use of alloys difficult to cast or machine. It is claimed to heat treat the same as solid. The molding mix is expensive but there is very little finish work required to have a working part so few if any shavings or filings are generated.

    Disadvantages include concealed flaws and uneven shrinkage; plus the high cost of molds which make some companies slow to correct a poor part.

    The process only applies to small parts, big stuff like the barrel, frame, and cylinder are not reasonable to MIM.

    A pre-MIM gun is therefore one made with parts cut from solid.
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  • asphalt cowboy
    Well, my wag was way off base. Only thing I could think of was pre-Made In M????

    Thanks immensely guys.
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  • tsr1965
    I will say this about the MIM gun vs. the pre-MIM guns...


    The MIM revolvers that are stock production, have a tendancy to be a lot smoother out of the box than the pre-MIM ones.

    S&W's sister company Thompson Center, also uses some MIM parts. I had a friend break off the swivel hammer on an Encore Pro hunter. I tried to drill and tap the old bolt hole out for another one. I had to fight with the drill, and there was no way the 8-32 tap was going to go. That tap would not bite at all. not sure what the alloy is they are using, but it is super hard.

    Best

    EDIT 1:

    dfletcher, HAWK, and Beantown,

    I was in no way implying that the new MIM guns were better than the old pre-MIM one's...especially for collector's purposes. However, I was implying that it took, on the average a few extra $$, a good pistol smith, and some TLC to get the DA pull on the older ones to where the MIM ones are out of the box. Also, if you found a pistol smith that was well versed and specialized in the S&W's, It could be better than both, the older ones, and the newer MIM guns.

    I am not sure how much experience any of you have with the S&W's, but I do know how to tune and time S&W revolver's. There are a couple sliding parts in there that on the older ones, most of the time showed light milling, and/or surface grinding marks. When they were stone polished out, the action rivaled the famous Python. Back 20 years ago, before the county Sheriff's department went to the auto's, I done the majority of the 686's, they had...starting with the top brass himself. It started as a favor for a friend, and spread like wildfire. Seems everyone not only likes a glass, silky smooth pull, but can shoot them better too. Gotta love them old S&W's!
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  • Hawk Carse
    I have also heard that MIM parts have a smooth factory finish.

    But if that hammer had not been quite so hard, it might not have been brittle and broken.
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  • dfletcher
    quote:Originally posted by Hawk Carse
    I have also heard that MIM parts have a smooth factory finish.

    But if that hammer had not been quite so hard, it might not have been brittle and broken.


    I've been buying Smiths since the early 70s and would agree that as had from the factory MIM gives the internals a smoother finish and none of the gritty feel such as the toe of the hammer dragging on the underside of the SA sear when the gun is thumb cocked. But I do feel that when polished and tuned the carbon steel internals of the older guns do feel slicker, that's just my subjective opinion.

    tsr1965 - I'm on board with that. I've been buying since about 1972 and doing my own modest tuning since then. I've owned a fair amount of Smiths and have always cleaned & polished the internals - I actually look forward to it. I think MIM is choice borne of economics that yields very good results for the average gun owner, but I suspect lots of folks here don't fall into the "average gun owner" category. I'd be happy with the old.
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  • beantownshootah
    quote:Originally posted by tsr1965
    I will say this about the MIM gun vs. the pre-MIM guns...

    The MIM revolvers that are stock production, have a tendancy to be a lot smoother out of the box than the pre-MIM ones.


    I haven't done enough "Pepsi challenge" of out of the box old Smiths vs out of the box new ones to be able to express an opinion on that, but I will say that in terms of pure trigger pull, the MIM guns are good (and better than most other manufacturers guns, MIM or not).

    My feeling (guess) is that there is (was) more variability in the older guns out of the box, just depending on who assembled them, whether they were hung over from the night before, etc. The MIM guns probably aren't as good as the best of the older factory guns, but they're probably as good as most of them, better than some, and more consistent.

    For what its worth, supposedly before Smith went to large-scale use of MIM parts in their wheelguns they did a blinded experiment where they asked a bunch of Smith-fans to try out the old guns vs ones made with MIM parts to see if they could tell a difference in the trigger feel. The result was that the revolver guys couldn't tell which guns had MIM parts simply by trigger feel.

    Again, I think the advantage to the earlier guns isn't so much in increased action smoothness or trigger feel, but just in more labor-intensive design. Now in practice, probably 99.99% of Smith revolvers will never need a barrel replacement, and recessed cylinders really don't add anything, but still, there is something "cool" or nostalgic about the older P&R guns.

    Obviously the lock (which is only present in MIM guns) is a whole other thing, though Smith actually has at least started to produce some new runs of NON-lock (MIM) guns, presumably by popular demand.

    Edit: For the record, I've fired plenty of older and MIM guns, I just haven't compared the two against one another brand new out of the box in one sitting. Assuming I even had similar brand new in the box MIM and non MIM Smith guns, the last thing I'm going to do is take them out of their boxes and dry fire them for this silly Pepsi challenge!

    For what its worth, I've never tried an MIM Smith wheelgun that had a gritty, stacking, or abnormally heavy trigger pull.

    Still, with one notable exception, every Smith wheelgun I own is pre-MIM. Its not that I have anything against MIM guns, its just I believe the older guns represent better values. Why should I pay MORE money for a new gun with MIM parts and a crush-fit barrel and a lock I'm never going to use, when I can get an arguably better one used for less money that will also retain its resale value better?

    The notable exception is that my personal carry gun (which often doubles for home defense) is a with-lock Smith 637-2. So in terms of putting my proverbial money where my mouth is, the gun I most often trust my life to is actually an MIM Smith revolver. (#2 and #3 guns are pre-MIM Smiths, by the way!)
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