How to tell diff. between a MIM and machined 870 extractor?

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Rob62
February 16, 2006, 09:44 PM
I'm curious if there is a way to look at an extractor on an 870 series gun and tell whether it is MIM or machined?

I own several 870's but over the years parts have been switched out so am not sure of what is in what. I'd like to strictly get the machined extractors for my 870's. But before I just spend the $$ on replacement parts I would be interested in seeing if there is any way to tell what is already in the guns.

Thanks and Regards,
Rob
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owen
February 16, 2006, 10:25 PM
The two give aways for MIM are parting lines and ejector marks.


A parting line is a line that runs all the way around the part (where the mold closes). Ejector marks are (usually) little circles, all on the same ide of the part. They are left there by little punches used to force the part out of the tool. They may be disguised as counterbores around holes, at least that's how I always tried to hide them.
Fred Fuller
February 16, 2006, 11:36 PM
You can see the difference with the part mounted in the bolt. The MIM part has a uniform dull finish with a mold mark running lengthwise, the machined part has toolmarks/file marks/grind marks and a less uniform looking surface.

lpl/nc
Rob62
February 17, 2006, 08:10 PM
Thanks for the explanations. I just checked my guns. It turns out that one of three does have the MIM extractor, an Express Magnum.

But I have a new complete spare bolt assembly courtesy of CDNN. This bolt has the machined extractor. I guess I'll just keep using the MIM extractor gun for a while longer and trade out extractors later.

Regards,
Rob
Dave McCracken
February 17, 2006, 09:19 PM
Maybe I'm missing something here. Has there been any problem with new extractors?
Rob62
February 17, 2006, 09:31 PM
Howdy Dave,

Actually I thought you'd know more about this issue than me.

From what I have read and anecdotal stories, I understand that MIM manufactured parts are not as good (a relative term for sure) as machined parts. Now I realize that this is very subjective, and that I'd probably get many, many, years of faithful service out of my MIM extractor.

However since this would be a relatively inexpensive part replacement. Actually, no cost as I already have a spare machined extractor. I figure that I might as well have the *best* part available in my gun.

Hope that makes sense. :)

Regards,
Rob
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