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MCM 38 super brass? Is really supercomp?


Jager1147

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Just got a new open blaster in 38 super, not 38 supercomp with an Aftec extractor. I've shot maybe 100 rounds of 38 super loads using rem. brass. The problem I have now is that I just bought a load of MCM 38 super brass from someone on the USPSA website, and I just noticed after loading up a bunch of rounds that the brass has a rim that looks more like i would expect a 38 supercomp round to look. The extractor groove is smaller like a 9mm, and the rim appears to be a smaller diameter than the rem. 38 super cases. The headstamp says MCM 38 super + P. I'm confused, the brass was advertised as 38 super. :huh: Anyone with info on this?

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Measure the rims with your calipers:

Rimless is about .386

Rimmed is about .406

You have about a 50/50 chance on it running through your gun, it depends on the condition of the gun and how it is set up and tuned.

My open gun will stove pipe on every piece of rimless that comes through it.

A buddy of mine only shoots rimless through his gun during practice because he knows that eventually it will jam.

However, you can set the gun up for rimless by simply installing a supercomp extractor (and tuning it, the main thing is to get the tension right).

Hope this helps.

THC

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MCM brass has "NR" on it for "No Rim". Those are practically rimless Supers. They have a small extractor groove which can cause problems with some extractors, but generally run in 38 Supercomp/TJ/Lapua blasters.

It's suprising how often this stuff turns up, given how old it is and how much was made.

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Measured the rims. the the rem supers were .401, and the MCM supers were .385

The headstamp reads MCM 38 SUPER + P R

Thanks again, thought I was aware of all the variations of 38 super, 38supercomp, 38TJ, 9x23, 9 supercomp etc.

Is this MCM brass identical to 38 Supercomp, or is it a different cartridge? The gun currently haas an Aftec extractor for 38 Super, but was considering getting a new Aftec extractor for 38 Supercomp. I will do this if i can mix the MCM brass with 38 Supercomp, just bought a bunch of this MCM stuff.

Thanks, Jager

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MCM was one of the first rimless cases..brought out by Matt McLearn..

surprised to hear you found some new stuff..for how long ago it came out...pretty much the same as 38 super comp..don't recall it being any thicker or the extractor groove having any changes..

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If your gun is set for rimless brass watch your cases, regular supers with the semi-rim may cause malfunctions.

If you set your gun up for rimless brass then use a .223 shell plate in your press. All of the rimless brass will go in but regular semi-rimmed supers will not.

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I am lucky with my Para 38 Super. I have loaded and run Super Comp right alongside the 38 Super stuff and it never misses a beat. Never adjusted the extractor differently either. I have actually shot entire matches with the SuperComp loads when it was a lost brass match.

So I don't even separate it anymore since I have never had the gun choke on it. I just run it all through the case pro and load it up.

About the only thing different on the SuperComp is they seem to chrono about 10-15 fps slower than the same load in Super.

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