View Full Version : About MIMs

September 27, 2006, 11:30 PM
I've read some about MIM parts in some 1911s, and I am curious as
to which parts are actually MIM.
One more question, how hard is it to find machined or forged parts
to replace MIM parts?


Hunter Customs
September 28, 2006, 08:14 AM
The most common parts that are MIM are, grip safeties, thumb safeties, sears, hammers, hammer struts, plunger tubes, extractors, ejectors, barrel bushings, slide stops, sights, disconnectors, main spring housings, and mag catches.
Finding good replacement parts is not hard to do, there's several companies selling good top shelf parts.
Bob Hunter

September 28, 2006, 11:16 AM
If your going to replace all those parts you might as well build it from scratch.

Jim Watson
September 28, 2006, 11:27 AM
Not all the listed parts are MIM in all guns. Mold marks are visible on most MIM parts.

Bear in mind that many of the internals are fitted parts and it is not just a matter of buying a new one of hopefully better material and reassembling the gun with it in place.

September 28, 2006, 11:38 AM
I'll pull on my Flame Suit here, but I have done some looking into this although I can't say that I "researched" it.

For the most part, Colt uses the fewest number of MIM parts than anybody else. If fact, they did use a MIM extractor on their government models up to a few years ago but went to milled steel after having some complaints about failures.

It's probably fair to say that the major manufacurers of 1911s all use MIM parts but that they also take some care that they are only used on lower stress applications. It would be foolish of a mfgr. to use MIM parts that were known to fail and continue using them if they cause unreliability.
We can only hope. :eek:

I haven't been able to come across a definitive and comprehensive list of who uses MIM in what applications other than just general information.
You'ld almost have to contact each individual manufacturer and ask the specific question.


September 28, 2006, 11:48 AM
"MIM parts that were known to fail "

As in the poorly made ones

They fail, just like poorly cast or forged parts:D

James K
September 28, 2006, 05:46 PM
Obiwan is correct. In the early days of MIM use in guns, many parts failed either because they were used inappropriately or because they were not made right. Making a spring (and an internal 1911 extractor is a spring) by MIM is simply dumb, and Colt of all people should have known better. But many other parts can be made by MIM with great savings and entire satisfaction.

Some people say that makers use MIM but don't reduce their prices. That is not the point. The point is how much the gun would cost if it were made of all forged, machined, and hand fitted parts; many of us talk about liking guns made "the old way", but I don't think most of us could afford them.

The idea of automatically replacing MIM parts without even firing the gun is absurd. One of the main drawbacks is that the buyer has no idea how any given part is made, and some manufacturers use clever wording. One common term, "all machined" means nothing except that the part is not MIM. It can be cast, machined from stock, forged, or made out of compressed beer cans; if it was drilled or run through a mill, it was "all machined." Nothing about the material, the type of steel, the hardness, etc. Just "machined."


Harry Bonar
September 28, 2006, 07:30 PM
Dear sir;
Don't like them - won't use them! Alot of sights, etc are made from 12L14 - good free machining steel.
Harry B.

September 28, 2006, 07:45 PM
MIM techniques are pretty mature at this point. They can be a better choice than drop forgings on some parts.

Not using something because of the way it is made is silly. How it performs and, in some cases, how it looks are far more important.


September 28, 2006, 10:08 PM
I had two series II plungers fail in my Kimber Eclipse. A softer metal that may have peened would be a better choice than one that broke cleanly and my have been brittle in the first place.

Jim Watson
September 28, 2006, 10:25 PM
Ersatz material for a superfluous part.
Attack of the mutant pistols.

James K
September 29, 2006, 02:34 PM
Let me see if I fully understand. Any old piece of trash, made out of any old material, is OK as long as it wasn't made by MIM.

Forgive me for repeating myself, but MIM is a metal working technique, just like forging, machining, or casting, or stamping. Like those methods, the end product is no better than the material that went into the process. We forget that Rugers were once widely condemned for being cast, "just like those old Spanish pot metal revolvers." Stamped parts were universally bad mouthed; the German P.38 was no good, we were told, because it was "all stamped out" and the Ruger Standard model was described as cheap stamped junk.

So, make Harry happy. Throw away your Rugers. Also your Glocks. And S&W's. And Colts. And P.38's. (Please throw them all my way.)

No, MIM is not appropriate to all applications, but neither are other materials or techniques. Designers need to know the limitations of any material they use. Glock proved that polymer can be used for pistol frames, but he didn't make barrels or springs out of it.


Harry Bonar
September 29, 2006, 05:37 PM
Dear Jim:
I understand - no, throw them my way!!!
Harry B.:)

alexander hamilton
October 9, 2006, 07:54 PM
heh heh, plastic barrels...


James K
October 9, 2006, 08:03 PM
Heh, Heh. You may very well see plastic barrels within the next ten years if concerns about security can be met.

Winchester made shotgun barrels from fiberglas with a thin steel liner, and barrels are often made from light metal with a steel liner. I don't know if any barrels have been made of a material normally termed "plastic" but they have been made from ceramics, complete with rifling, and worked.


October 9, 2006, 09:04 PM
Not to throw in and make anyone mad, but Winchester ain't making anymore of those barrels for a reason, Jim. Is it something we all like, of course not as well as technology isn't today what it was yesterday.

I wish I could afford to buy a gun that was built by hand all the time by a machinist that knew what he was doing and could hold tolerances very close. I think we all know those days are over with because it requires money that manufactureres don't want to spend amymore when they can mold them and throw them on without having anyone have to fit the parts any more. Is it better because of this, according to Harry and many others NO! What happens when you have to replace a part with a new part because a gunsmith can't work on the MIM parts, exactly, no more need for a man that knows how to make them work anymore when all he has to do is swap in a new one.

Are all MIM parts useless, of course not, some actually can and do work, but count me in on the side that doesn't like them and wish all things were like they used to make 'em back in the good ol' days when if it broken and there weren't any new parts handy, a man could weld it back together and case harden it and put it back to working for him.

October 10, 2006, 07:40 PM
As far as I'm concerned, plastic barrels are only unavailable because of longevity and security reasons at this point ... PEEK (poly-ether-ether-ketone, IIRC) is a hi-temp polymer that, when glass or carbon filled has excellent strength at high temps and very low friction. I happens to be a "controlled substance" in south east asia for security reasons ... fear of gunrunners making undetectable firearms ... or so I was told by the supplier I was working with a few years ago.

As pricey as PEEK is for a plastic, PEEK barrels would be injection molded and would probably be quite reasonably priced and therefore viable if you were willing to replace them every so often.

Just a thought ...


James K
October 10, 2006, 08:09 PM
Hi, Cntryboy,

Those fiberglas barrels mostly worked OK. The main reason they weren't liked was that they were TOO light and shotgunners couldn't get a decent follow through. And, of course, the gun wasn't really liked either and had quite a few problems.

There were a lot of silly stories about the fiberglas unwinding and so on, but those were just the type of nonsense stories we see all the time. We sold quite a few and had no comebacks or complaints about the way the barrel was made, though we had quite a few about the action.


October 10, 2006, 09:19 PM
I have some experience with MIM parts in revolvers; allow me to add a "real world" perspective. I'm not at all averse to the use of MIM parts, where appropriate. Note those last two words!

As someone else has noted, it's just another metalworking method, and has strengths and weaknesses. Far too few engineers understand them, with a corresponding drop in understanding amongst the general public.

First off, a steel MIM part can be treated like any other steel part; it can be welded, soldered, blued, hardened, and tempered. This is important to understand, as there is a perception out there that the parts are not "real" steel. They are!

The advantages of an MIM part do not generally include raw cost; the material is expensive, and the molds are horrendously expensive. The benefits come in the area of post-fabrication. The MIM part, as noted, can be heat treated - the benefit is that they don't need to be, as the hardness of the part can be engineered in when the part is made. The parts come out ready to use; no additional surface finishing is generally needed. Finally, the parts can be made in shapes that would be extremely expensive or nearly impossible to economically machine.

The downsides? Cost, as already noted. Additionally, the tolerances for an MIM part generally need to be larger; it's hard to hold them to .001" in all dimensions (though they're getting better all the time.) Another problem is that the technology doesn't work all that well for parts that are more than about 3/8" thick (again, this gets better on an almost monthly basis), nor on stressed parts that are very thin.

There are other, less obvious pros and cons of MIM parts, but you get the idea - MIM, like anything else, is a balancing act.

Now here's the part that those of you who aren't fond of MIM should understand: the problem isn't with the technology, but with the engineering behind the part itself.

As noted, MIM on a per-part basis is pretty expensive, but since they can be engineered with specific traits they can eliminate some expensive secondary operations - hardening, for example. Here's the problem: let's say that you are building 1911 sears, and MIM seems a good method for producing them. You decide that the sear has to have a certain hardness (so that it doesn't wear), and since the surface finish is good "as produced" you think you're home free.

The trouble is that the MIM part is the same hardness all the way through, since that's how it was engineered. This is great for reducing sear face wear, but with hardness comes brittleness - and that thin edge is quite brittle. What you need is a surface hardening of some sort for wear resistance, with the underlying material left softer for strength. You COULD do that with an MIM part, but if you did you'd negate one of the primary benefits of the method: the elimination of secondary operations. So the company chooses to continue to use the MIM part as designed, and which is a poor choice for the application. No wonder some people don't like them!

The bottom line: if you have trouble with MIM parts, it's not the part's fault - it's the fault of the engineers in the company that designed the part. (Frankly, I wouldn't want to buy an entire gun from a company that botched the engineering that badly, regardless of whether or not I replaced the parts in question. I'm funny that way!)

October 11, 2006, 12:18 AM
Jim what I didn't like about those particular barrels is they looked like the dickets when the end was worn down and that happened a few times. I also like a little more heft on the muzzle end myself. Like what was said though, the barrels weren't the worst part of that particular gun.

I agree with the last post on MIM and this is where I have a problem with it the most. Revolver parts for years was casehardened mild steel where the case was rugged and the part could withstand the shock of operating. With the MIM parts, you don't get that. I have seen a few cracks because of this already, not sure how many more down the road will be more apparent, but I would think it is on the way. Those new S&W 500's produce quite a bit of recoil and shock on the parts, I am interested in seeing how long they stay with it or have problems.

James K
October 11, 2006, 01:23 PM
I haven't heard of any problems with S&W's but there have been some problems with MIM parts in other makes. One company uses (used?) MIM for its 1911 type barrel bushings. Some broke at the apron, throwing the spring plug down range. The same and other 1911 type makers have had problems with slide stops, sears and even safeties. I think the problems with the sears, safeties and bushings were manufacturing problems with poor quality MIM work, I think the slide stop is probably not a good place for MIM.

One big advantage is that MIM allows complex parts to be made that either couldn't be made or could be made only at a very high cost. The new S&W revolver hammer, for example, uses a hammer strut (S&W calls it the "sear") that eliminates two holes, a pin, and intricate machining, yet functions just as well as the old one. But a look at the setup clearly indicates that the new design would be next to impossible without MIM. That is the kind of thing MIM can do in the way of keeping costs down while maintaining quality.

But as I said before, just blindly farming out parts to someone who claims to do MIM won't work. Designers and engineers have to learn the characteristics of MIM, figure out its strengths and weaknesses, decide what applications are suitable and which are not, and make sure the proper material is used and then properly heat treated. In other words, they should do the job they are paid to do.


October 11, 2006, 02:21 PM
Caveat: Im not a real gunsmith, but I see broken guns every day

I dont like, all in all, MIM or pot metal parts. Some MIM is better than others...S&W has good MIM, Kimber does not.

But its a money saving measure that allows bells and whistles at a competative price.

Now of course, real machined forgings are a joy. The only guns I can confidently gunsmith are Broomhandles and Lugers....take one of those apart, look at the precsion maching done by hand (and rust bluing besides) and figure out how much it would cost today.....


alexander hamilton
October 11, 2006, 08:11 PM
ok, as an auto mechanic i see something we know as "pot metal" everyday. i was unaware that it was related to metal injection molding. am i even on the right track here? whats the difference? or rather, whats the connection?

October 11, 2006, 08:15 PM
"Pot Metal" is unrelated to MIM ... pot metal is a term that has been used to refer to metals (often zinc alloys if I'm not mistaken) that have a relatively low melting point. These have been used for decades to cast parts (hopefully those which don't need much strength to speak of) very cheaply. MIM is a relatively new process that is a form of injection molding at very high pressures and temperatures.


alexander hamilton
October 11, 2006, 08:17 PM
ok, that was my understanding of it. guess i just got confused.

James K
October 11, 2006, 08:54 PM
Pot metal is not zinc, it is the cheapest kind of cast iron. It is called "pot" metal for the fairly obvious reason that it was the material used to make the old fashioned cooking pots, like you see on the stove or in the fireplace in the old pictures.

FWIW, the pre-MIM S&W hammers and triggers were not forged. They were blanked (punched) out of steel plate then cold forged to shape if necessary (target type) and machined, a costly process. S&W used a fairly soft metal and case hardened it, claiming that the soft metal prevented breakage. Not always; I have seen two S&W hammers with the spur peeled off while cocking, and one broken at the waist. Colt (DA revolvers) used tool steel and hardened it all the way through, claiming that it was superior to case hardening and could be worked on. I have seen two Colt hammers broken at the waist. So, nothing is perfect.

The big advantage of MIM is that it comes out of the process ready to go, no machining needed. The old S&W triggers almost always benefitted from stoning to smooth out the cross ways machine marks; the MIM parts are smooth, with no machine marks and don't need smoothed up. Even the single action notch does not require machining.


Hunter Customs
October 12, 2006, 08:56 AM
First I'll say I'm not an engineer so what I've learned about MIM is what I've learned from others that know MIM and the broken parts I have seen first hand come across my bench.

MIM is powered metal, mixed in a slurry, injected into a mold and heated to high heat to form the part. The main problem with the MIM process is trying to control voids in the part. The voids do not appear in the same place all the time even in the same batch of parts being made. To my understanding the only way to be sure the part is free of voids is to check each individual part. This is time consuming and would add to the cost of the part; most large manufactures do not wish to take the time or expense to do this. Again keep in mind MIM parts are used because they are less expense to the total cost not because it's the best method of making parts.

I've built 1911 guns for a lot of years; before MIM came along it was rare to to replace a part because the part failed. Parts were replaced because someone wanted something different or to change the tolerances in the gun.

I'll list the MIM parts that I've replaced because of part failure (parts that were cracked or broken) in 1911 guns and to be fair I'll only list parts that I've replaced three or more of.

MIM Slide Stops- All I've replaced because of failure had sheared the pin causing the gun to tie up. Before MIM the only slide stop I replaced because of breakage was a cast slide stop. Part of the locking lug broke causing the gun to not lock open when the last round was fired. However the gun could still be fired if the need be.

MIM Sears- I've seen failure on these in two different places. I've seen the nose or the ledge as some call it break causing the sear to fail to engage the hammer hooks. I've also seen cracks and breakage around the sear pin hole. Before MIM I can not recall ever replacing a sear that was cracked or broken.

MIM Slide Lock Safety (Thumb Safeties)- I've seen both single and the ambi fail because of breakage. I've seen the pins sheared and the tabs that operate the ambi side shear.
Before MIM I've never replaced a safety becuase of failure.

MIM Hammers- I've seen the hooks sheared off and the face of the hammers with cracks in them.
I've never replace a non MIM hammer because of part failure. However I have replaced a few with short hooks that some over zealous gun pro cut way to short.

MIM Extractors- the breakage I'v seen on these was at the Claw and the knuckle.
I've replaced two non MIM extractors because of breakage. In one of the guns the guy that owned it was dropping the slide on a round in the chamber. I don't know how many times he had done this, but to his best recollection it was several and he finally broke the claw on his extractor.
The other extractor was in a racegun that I was told had over 80,000 rounds fired thru it. The top corner of the claw was chipped off but the gun was still extracting.

MIM Disconnector- None had complete breaks just cracks in them. I've never replaced a non MIM disconnector from failure.

MIM Barrel Bushing- I've seen them cracked, the locking lug sheared off and the lower part of the bushing break.
I've replaced one cast barrel bushing that was cracked.In all fairness it was in one of the more least expensive 1911's offered today.

To the best of my recollection I believe I've seen failure in every MIM part made for a 1911 but as I stated earlier I did not list them unless I had seen at least three examples of each part.

I know a good machinest who says " the only thing I know for sure is what I can measure", and from what I've seen of 1911 MIM parts is that they certainly do not measure up to top shelf cast or forged parts.

When people tell me that MIM is just as good as other methods of making parts I have to wonder why we do not have MIM frames, slides and barrels when I have seen cast and forged frames, slides and barrels.

Bob Hunter

James K
October 12, 2006, 08:40 PM
Hi, Hunter Customs,

I don't know who said MIM is just as good as any other way of making parts, but I didn't. I said that there are applications where MIM should not be used and specifically mentioned slide stops and internal extractors. I also said that like other kinds of metal working, MIM can be done well or done badly.

Maybe I missed something, but you seem to be saying that you never saw any kind of part breakage on a 1911 type pistol except when the part was made by MIM. I wonder if you are not doing some selective remembering.

Yes, I have seen broken MIM parts, but I also have seen a goodly number of broken parts, both in the service and in civilian work, that were not MIM. Even GI parts sometimes break, though not often, but most breakages are with the cast junk sold at gun shows and sometimes put out by big name makers. They advertise the stuff as "machined", trying to fool the customer into thinking the part is machined from stock when it really is just a cleaned up casting.


Hunter Customs
October 12, 2006, 09:04 PM
Hello Jim,
I did not direct my post on MIM parts to you or anyone else on this Forum. But numerous times I've heard it said that MIM parts are just as good as forged or cast parts. I simply stated my experince with MIM, cast and forged parts; I figure the readers can make their own conclusions.

As for selective remembering maybe you should re-read my post as you will see I did list failures with parts other than MIM however my post covered only what I know and have seen.

Bob Hunter

alexander hamilton
October 13, 2006, 07:40 PM
is powered metal, mixed in a slurry, injected into a mold and heated to high heat to form the part.

so its sintered?

October 13, 2006, 07:55 PM
MIM consists of powdered metal that is mixed with a binder (usually a plastic compound) which allows it to be injected into the mold. It is then heated to just under the metal's melting point, where it coagulates to form a solid mass - a process known as sintering. The binder is burned off in the process.

Sintered parts, as most people historically know them, are made of powdered metal that is poured into a mold, then heated to the sintering point.

The key difference in the two processes is the use of the binder material in MIM, which allows the injection into the mold. Because of that property, the MIM part can be significantly more intricate than a plain sintered part.

So, what it boils down to is that all MIM parts are sintered, but not all sintered parts are MIM. ;)

October 14, 2006, 12:15 AM
My problem is that my Series II safety plunger on my Kimber broke TWICE rendering the fire arm useless. If it was forged or even cast, it may have bent......but it snapped cleanly in two......and this was the worst possible scenario.

October 14, 2006, 09:41 AM
I read a post by XavierBreath (sp?) a couple of days ago. He has a link in his signature for his guns. At the bottom of his list he had "catastrophic failures". Iv'e never seen a 1911 slide break like the Kimbers in the list. A guy I new let me shoot his Kimber Ultra Match and Glock 30 one day. The Glock was more accurate than the Kimber! I am not trying to bash Kimber owners, but I'll never be on of them. Especially with the stuff I hear on here.

alexander hamilton
October 15, 2006, 09:43 AM
thats funny, i have always thought of kimber as being a good middle of the road 1911. shows how much i know about 1911's. i figured they were definitely a step up from the cheap junkers and the otherwise nice usgi. guess i should do more research before i decide to add a 1911 to my collection.

Hunter Customs
October 17, 2006, 10:03 PM
Let me see, sintered parts and sintered bullets is that considered frangible?
Bob Hunter

October 17, 2006, 10:46 PM
Funny. I shot thousands of Sinterfire bullets. They shot GREAT. But...if you crimped beyond any neutrality you would stress the bullet and you would find two holes in the target.

Strip out the Series II safety and you have a VERY accurate 1911 in a Kimber.

October 18, 2006, 04:28 PM
Colt MPI's their bolts (AR/M4) to weed out the bad ones

The ones that break at the Cam Pin Hole

Sometimes after very low round counts

And no...they are not MIM

There is good and bad quality to be had in any process