About MIMs

[James K]

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.

Jim

 

[Wildalaska]

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.....

WildlovescraftsmanshipAlaska

 

[alexander hamilton]

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?

 

[saands]

"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.

Saands

 

[alexander hamilton]

ok, that was my understanding of it. guess i just got confused.

 

[James K]

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.

Jim

 

[Hunter Customs]

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.

Regards
Bob Hunter
www.huntercustoms.com

 

[James K]

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.

Jim

 

[Hunter Customs]

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.

Regards
Bob Hunter
www.huntercustoms.com

 

[alexander hamilton]

quote:
is powered metal, mixed in a slurry, injected into a mold and heated to high heat to form the part.

so its sintered?

 

[GrantCunningham]

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.

 

[Lycanthrope]

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.

 

[Rimrod]

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]

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]

Let me see, sintered parts and sintered bullets is that considered frangible?
Regards
Bob Hunter
www.huntercustoms.com

 

[Lycanthrope]

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.

 

[OBIWAN]

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