MIM parts

[fatelk]

I posted about this issue in the handguns forum, but had a more specific question so figured I'd ask you all here.

I pierced a primer in my S&W 29-8 and it torched the firing pin something ugly. I then fired another round and the destroyed firing pin stuck in the primer so that the gun was frozen up solid. It took quite a bit of work to get it freed.

The firing pin was perfect before, and burnt to a crisp after one pierced primer. Is this a fluke, or could it be blamed on the MIM firing pin. I know they say that S&W MIM (Metal Injection Molded) parts are supposed to be just as good a traditionally manufactured parts, but I had just never seen a part torched like this with one primer. It wasn't even a hot load, just a bad primer.

The reason I ask is that I'm getting ready to order a new firing pin, and I can get a replacement S&W MIM pin, or a machined aftermarket stainless steel one.


Attachment 222389

[metricmonkeywrench]

MIM or not sometimes firing pins fail, it is a somewhat a wear item. More than likely several (hundreds?) rounds before it chipped and the downward spiral began. I had a series of failures to fire on my model 64, replaced the firing pin and all is good.

Traditionalists will decry the use of MIM parts and there are lots of 10th party second crapper on the right stories of failed MIM parts, but very few actual proven examples.

A factory part will be sufficient, there is no need to get a extended or unobtainium "never fail" firing pin that are out there on the market to correct a perceived flaw.

Found my notes, if the firing pin is less than .492, then replace it. Many people think ideal length is .495.

[leebuilder]

Wow. I didn't know they made mim firing pins. They are making bolts out mim and they are snapping. I would go with the solid one.
Be well

[Tatume]

MIM parts in the "hot section" of turbine engines hold up to pressure, heat and stress at 50,000 rpm.

[lefty o]

ive had in my hands more than couple failed MIM firearms parts, but really hard to blame your firing pin on it without more evidence.

[JRD]

That firing pin isn't a MIM at all. It's a machined part made on a screw machine. It's machined from titanium.

The gas from the pierced primer is what cooked the tip of your firing pin. Pierced primers are unusual in a revolver, but they can happen, usually with magnum loads using thinner cupped primers. When the primer ignites is stretches back over the firing pin up against the bolsterface, and then your case sets back against the bolster reseating the primer. This can stretch the primer material and pierce it if the pressure is too high for the stretched primer cup material.

If you are reloading full pressure 44 mags, what are you using for a primer? Maybe try switching brands and reserve the brand that pierced for lower pressure reloads.

Get a replacement firing pin and your revolver will be back in service.

[fatelk]

I was just assuming it was an MIM part, because the replacement is listed at Brownells as "Smith & Wesson - Firing Pin, MIM, For Frame Mounted Firing Pin".

The primers are no longer an issue. They were some 30+ year old Federal LPM primers that were apparently known to have this problem back in the day, as I came to find out. I'm in the process of pulling down 200 rounds of mid-range .44 mags, and I'll either bury the primers in a hole or use them up in light .45 acp target loads, haven't decided. I don't have many of them left so it's really not a big deal.

I've used the mid range .44 load in question with other primers for some time with never a problem. I knew these Federal primers were a problem because I had trouble with them piercing previously when working up a magnum H110 .44 mag load. I figured they should be fine in a lighter mid-range load, but was clearly wrong. The funny thing is, when the heavy loads pierced in my older 629, they didn't damage the firing pin on it at all. That's why I was wondering if it was just a fluke or something else.

I think I'll go ahead and order the S&W replacement pin. Heck, for $6 each I'll order two and have a spare. I'm just glad all it damaged was the cheap and easily replaced firing pin. All's well that ends well. The biggest pain is having to disassemble 200 rounds of .44 mag ammo. I'm about half done with that, but I have to buy a new kinetic bullet puller because I broke my old one in the process!

[JRD]

fatelk,
What they mean by Firing Pin MIM, is that the firing pin is for the MIM hammer. Back in the early 90's S&W switched designs from the old "hammer nose" which was a pivoting firing pin mounted on the hammer face to the flat faced hammer with a frame mounted firing pin. The flat faced hammer is made by a Metal Injection Molding (MIM) process. The round firing pin is a machined part. It doesn't make sense to build a MIM tool for a part that you can cheaply machine from round stock. Complex shapes like a hammer, trigger, etc. are where MIM has advantages.

Traditionalists don't like MIM because it's not the old way, but as an avid fan of advances in manufacturing technology, I think MIM is a pretty cool process. I still enjoy owning older S&W's made the old way, but I don't begrudge the company for using new technology. It's progress and it happens in every industry, not just guns.

[fatelk]

Ah, that makes sense; Thank you! I was a little baffled as to why such a simple little part would be MIM. Heck, if I had to I could have made one with just my drill press and hand tools.

I feel much better about buying the S&W replacement. At least it's a cheap, easy fix.

Thanks everyone!