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View Full Version : "Beware the Rats of MIM."


lelandEOD
04-14-2012, 3:19 PM
So, I was out at the range shooting my AR carbine a good while when I noticed that my bolt hold paddle was flopping about.

Upon further inspection, it became apparent that the paddle itself failed for unknown reasons. When I pulled it apart, it was obvious.

Beware the Rats of MIM.

http://i371.photobucket.com/albums/oo159/993_guy/52b0377a.jpg

http://i371.photobucket.com/albums/oo159/993_guy/dc5da7cf.jpg

http://i371.photobucket.com/albums/oo159/993_guy/1c18d30a.jpg

The next time someone tells you there is no difference between the bargain basement LPK's and quality parts, just remember these photos. I don't want to reveal who's LPK I used because it could have been one or two makes. It's been a couple years and I don't remember which kit went on which rifle. But, I remember congratulating myself for getting such a good deal. Fail.

:90:

StratORcaster
04-14-2012, 3:21 PM
Yikes.....

ap3572001
04-14-2012, 3:32 PM
For the difference in price today, there no reason not get ONLY top quality AR Stuff.

Fate
04-14-2012, 3:38 PM
Hollow cast? Wow. That's pathetic.

MrPlink
04-14-2012, 3:56 PM
wow, never seen one like that before. Very odd cost cutting method.

bombadillo
04-14-2012, 4:07 PM
Why not say the name of the company. It may keep others from having the same problems you had. I've had issues with DPMS, but pretty much any other one I've bought including Del-Ton has been just fine. I ALWAYS upgrade the trigger so thats never an issue but the LPK's have all been fine for me from the best to the most basic PSA's.

Munny$hot
04-14-2012, 4:22 PM
To tell if the part is MIM look at where the mag floor plate touches the bolt hold open. The indented circle (visible in the first 2 pics) is a sign the part is MIM. Just note just because it's MIM doesn't mean its inferior to machined parts it's more of quality control. The cost of machining is very expensive.

wjc
04-14-2012, 4:23 PM
...and our moral of the story.

"You get what you pay for..."

Glad you found the problem!

sammy
04-14-2012, 4:31 PM
So which parts kits are MIM and not? I ask because I am shopping now.

Maddog5150
04-14-2012, 4:37 PM
I bet it ended with a "ton" and started with a "del"

MIM parts suck really bad. When I was working at an FFL full time, I witness MANY high quality 1911 pistols with broken controls out of the box or brought back for repairs because of simple MIM parts just snapping. Great quality pistols over all but needed to lose the MIM parts.

lelandEOD
04-15-2012, 1:45 PM
It was either DPMS or Del-ton. I can't be sure which.

ptoguy2002
04-15-2012, 2:33 PM
Is that a cavity in the molding?

fighterpilot562
04-15-2012, 3:06 PM
damn thats bad.

MrPlink
04-15-2012, 3:08 PM
It was either DPMS or Del-ton. I can't be sure which.

cant speak for Delton, but thats not DPMS. DPMS sucks, but not THAT bad

Fate
04-15-2012, 4:01 PM
Is that a cavity in the molding?

No, it's just hollow: powder metal injected molding. Like plastic injection molding, but done with powdered metals.

P.O.S.

http://en.wikipedia.org/wiki/Metal_injection_molding

chead
04-15-2012, 4:55 PM
Hollow cast? Wow. That's pathetic.

Seriously, that's terrible.

milotrain
04-15-2012, 5:07 PM
RRA with national match trigger $130
(http://www.joeboboutfitters.com/Rock_River_Arms_Complete_Lower_Parts_Kit_with_Nati _p/rra-completenm-kit.htm)RRA with single stage trigger $68 (http://www.joeboboutfitters.com/Rock_River_Lower_Parts_Kit_Single_Stage_Trigger_AR _p/rra-ar0120.htm)

Working the price on an LPK is bleeding the stone. You spend an inordinate amount of your own time figuring out a way to save $9.99

wash
04-15-2012, 5:27 PM
As far as I know, there is no way to "hollow cast" things like that.

You wouldn't do it intentionally any way.

A simple QC check for that would be to weigh parts and reject parts that are light.

I've never had a problem with DPMS except for crummy trigger pull but that's a sample size of about 3...

Pete1979
04-15-2012, 6:05 PM
Same thing happened to the slide stop on my Springfield 1911 about two weeks ago, just a defective part. The only problem is on the AR. that roll pin is a PITA to work with...

Sonic_mike
04-15-2012, 6:11 PM
does the stag lpk have any mim parts?

MrExel17
04-15-2012, 6:19 PM
Good to know thanks for the info!

Steelheader
04-15-2012, 8:18 PM
Same thing happened to the slide stop on my Springfield 1911 about two weeks ago, just a defective part. The only problem is on the AR. that roll pin is a PITA to work with...

That's why I ordered one of these:

Bolt Catch Pin Punch (http://www.uniquetek.com/site/696296/product/T1368)

wash
04-15-2012, 8:48 PM
You'll notice the bolt hold open did not break at the roll pin hole.

This is clearly a manufacturing defect rather than a design issue.

And if you have a T25 security TORX bit and a magnetic tip screwdriver handle, you can do exactly what a special roll pin starter punch would do. It's cheaper and you can find it at the local hardware store too.

arsilva32
04-15-2012, 9:14 PM
hey i like that Bolt Catch Pin Punch, i'm always worried that i'll slip and scratch the krap out of my receiver.

Steelheader
04-15-2012, 9:22 PM
hey i like that Bolt Catch Pin Punch, i'm always worried that i'll slip and scratch the krap out of my receiver.

That's why I bought one. I used to use the needlenose vise grip method, but no matter how well I taped the jaws, they always would mar the pin housing. With the tool and a quality non-marring hammer, I'm GTG. :)

joefrank64k
04-15-2012, 9:32 PM
As far as I know, there is no way to "hollow cast" things like that.

You wouldn't do it intentionally any way.

A simple QC check for that would be to weigh parts and reject parts that are light.

I've never had a problem with DPMS except for crummy trigger pull but that's a sample size of about 3...

Agreed...that's a QC issue for sure, not some intrinsic problem with MIM. The metal powder didn't fill the mold all the way before it was fired. Like you said, weighing the parts would spot that defect easily. MIM allows for amazingly complex small parts that can be sold for less than machined. As long as QC is followed, MIM parts are fine.

lelandEOD
04-15-2012, 9:59 PM
It's not hollow, just a bubble like someone pointed out. Just poor QC.