The MIM in 1911 Bugaboo
The first pistol that I noticed containing MIM parts was an early 1991A1 Colt. I saw it again in another Colt bought just a matter of weeks later. I bought the pistols specifically for beater duty, and I’ve beat’em long and hard ever since. The pair is approaching 400,000 rounds, about evenly split.
I did partial rebuild at roughly 75,000 rounds, Peening the frame rails and refitting the slides, and I replaced the extractors…not because of any problems…but just because. I replaced both barrels and replaced the ejector on one because it was a little loose in its moorings, and I wanted a tight one.
One of the pistols is still operating on the original MIM sear and disconnect. I replaced the disconnect in the other. It looked to be a little worn, and I wanted to nip any possible future problems in the bud.
A friend came to me about 8 years ago with a sear and disconnect and a request to replace the MIM parts in his Colt…even though he hadn’t had a problem…but just because he’d heard the horror stories.
So, I did.
Then, I demonstrated that his MIM parts really weren’t anything to be concerned with. Scientific demo.
I laid the sear on an anvil…cupped side down…and whacked it 3-4 times with a 4-ounce hammer. It didn’t shatter. It didn’t even crack. When I installed it in a pistol, it functioned just fine, albeit with a rougher trigger.
Then, I clamped the disconnect in a vise and whacked it with the hammer.
It bent, but it didn’t break. I had to beat it to about a 60 degree angle before it broke.
Good MIM can be very good. Some of is eve better than machined barstock in certain applications.
Bad MIM is worse than junk. The problem is that…barring a visible defect…it’s impossible to tell the good from the bad.
Kimber seems to have pioneered the use of MIM in guns, most notably in their 1911s I don’t know for sure that it was used in any of their other guns, but I’d bet so. Early on, they apparently had a vendor that provided good MIM parts, because we don’t hear of many failures in their early pistols. Then, for some reason, it changed…and the reports of Kimber’s MIM parts bustin’ like dry match sticks. Now, it seems that they’ve gotten it straightened out. I don’t know whether they found a new, better supplier or they read the riot act to their old one…but it’s gotten better.
Colt had a good vendor from the git-go, and they’ve apparently stuck with’em. I rarely hear of a Colt MIM parts failure. Part of that is directly related to Colt understanding that there are some applications that MIM isn’t suited for. Their one deviation was the short time that they used MIM extractors. They learned a hard lesson…corrected it…and moved on.
Other manufacturers don’t seem to grasp that concept, and continue to use the stuff for parts that don’t fare very well when made of MIM.
Generally…assuming good material…MIM works as well under frictional stress as any. Sears and disconnects are examples. Under impact or shearing stress…not so well. MIM hammers don’t hold up…and you won’t likely see an MIM slide or barrel for a long, long time…if ever.
Torsional stress is another area that doesn’t do as well when made of MIM as with machined steel, though it does fare better than with impact. MIM thumb safeties sometimes break off when they endure rough handling such as forceful operation during action games, but they do pretty good under normal use by the average non-game shooter.
Grip safeties break because the tangs are impacted by the hammer. Again…some break and others hold up. It’s mostly in the material and where on the tang the hammer strikes. Upswept “Ducktail” safeties sometimes take the impact high, where the leverage and the hammer’s speed is at or near maximum. A matter of physics and mechanical advantages. The problem is that most upswept grip safeties are, in fact, MIM.
This is one of the reasons that I don’t care for ducktail grip safeties. One of the reasons.
So, there are a few MIM parts that aren’t a concern…again assuming good MIM…while others are.
Generally, if a non-impacted MIM part is going to fail, it’ll do it early on. If it holds up for 500 cycles, it’ll probably last for 50,000 or beyond. For an impacted part…again, if it endures 500 cycles…it’ll probably stand 10,000 such impacts.
These numbers exceed what the manufacturers consider “normal” use over the life of the gun…which is why they opted for cheaper MIM. For those who shoot hard, the thinking shooters understand that parts will fail eventually, and are prepared to pay for replacing those parts periodically.
The key to avoiding a part failure…MIM or otherwise…is to learn to detail strip the gun and closely inspecting the parts about every 2500-3,000 rounds. As a bonus, you get the gun spanking clean inside and out. Clean and oiled is good.