M-10/9 Mystery Upper Question

[Mr. Greg]

I've been meaning to post this for a while, but just didn't find the time. When I bought my M-10/9 a few years ago, it came with this upper. It has no markings, is side-charging, and, strangely, has a pistol grip on the right side of the upper, making it seem perfect for lefties (but watch your arm around the ejection port, I guess?). I did a bit of googling, not too deeply, but didn't find anything readily apparent as to its history/manufacturer.

Anyone have an idea of who made this?

 

[MitchWerbellsGhost87]

It was made by “RPB” back in the late 90s. (Not to be confused with the real RPB from the 70s/80s). They were the first distributor of masterpiece arms guns and parts.

 

[Mr. Greg]

Thank you! I had a feeling you of all people would be the one to have the answer ?

 

[Weso]

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I've been meaning to post this for a while, but just didn't find the time. When I bought my M-10/9 a few years ago, it came with this upper. It has no markings, is side-charging, and, strangely, has a pistol grip on the right side of the upper, making it seem perfect for lefties (but watch your arm around the ejection port, I guess?). I did a bit of googling, not too deeply, but didn't find anything readily apparent as to its history/manufacturer.

Anyone have an idea of who made this?

Thanks for asking. Got one in the .45 and was wondering the same thing.

 

[Mr. Greg]

Thanks for asking. Got one in the .45 and was wondering the same thing.

Have you been able to rotate the forward handgrip? I'm trying to get it out of the right side lefty position to a under-barrel position as seen in the catalog picture above, but man that nut behind the flash hider is seized so tight. I've about given up on it after marring the nut a bit.

 

[skoda]

Penetrating oil today, heat (if you can) tomorrow. Along with a good fitting wrench.

 

[MitchWerbellsGhost87]

Have you been able to rotate the forward handgrip? I'm trying to get it out of the right side lefty position to an under-barrel position as seen in the catalog picture above, but man that nut behind the flash hider is seized so tight. I've about given up on it after marring the nut a bit.

You’re gonna have to use a blow torch. Only way I ever get these old barrels and barrel shroud nuts to loosen up personally. Hit it with the torch for a few seconds and it usually breaks loose fairly easily.

 

[BlackBelt]

I have one in .45 that I replaced the foregrip with a Thompson grip.
The difference between mine and the others Ive seen is mine has a simple crude blade for a front site, and the others Ive seen have no front sight. When I ordered it the pic did not have a front site, but it was a nice surprise when it arrived.

 

[MitchWerbellsGhost87]

I have one in .45 that I replaced the foregrip with a Thompson grip.
The difference between mine and the others Ive seen is mine has a simple crude blade for a front site, and the others Ive seen have no front sight. When I ordered it the pic did not have a front site, but it was a nice surprise when it arrived.View attachment 41473

That is one of the early Masterpiece arms upper receivers with the blade front sight. They used those on some of the pistol length uppers as well.

 

[MAC MAN]

Front Blade sight was used on the Jersey Arms Guns.

 

[Mackjack]

Have you been able to rotate the forward handgrip? I'm trying to get it out of the right side lefty position to an under-barrel position as seen in the catalog picture above, but man that nut behind the flash hider is seized so tight. I've about given up on it after marring the nut a bit.

I have one I took apart as your trying to do, there was some type of locktite and it required mild heat to get it to come free.

 

[Mr. Greg]

I was successful today, took lots of torching from my little crème brûlée torch (because I dont have a blowtorch), and some pretty hard wrenching, but I loosened it enough to rotate the forward grip to the underside position and tightened it back up. Phew, what a journey.

 

[charles_the_hammer]

Looks like a FAL grip on there.

 

[LawBob]

Penetrating oil today, heat (if you can) tomorrow. Along with a good fitting wrench.

Kroil and patience grasshopper

 

[Mr. Greg]

Alright, new question - Any idea of the thread pitch on the barrel of the upper? I've tried a 3/4×10 adapter like is used for standard Mac threads, but it's too big, as I figured it would be. I tried 1/2x36, but that's too small.

This is a picture of the threads, 1/2x28 on the right side for reference.

 

[MitchWerbellsGhost87]

Alright, new question - Any idea of the thread pitch on the barrel of the upper? I've tried a 3/4×10 adapter like is used for standard Mac threads, but it's too big, as I figured it would be. I tried 1/2x36, but that's too small.

This is a picture of the threads, 1/2x28 on the right side for reference.

View attachment 41583

I think they’re 5/8x24 but not positive

 

[Deerhurst]

.625-24 by the looks of it but there is no way we can tell by a photo. Youll have to measure it or try a known thread on it.

Measure the OD with calipers and use a thread checker to check the thread pitch.

 

[MitchWerbellsGhost87]

.625-24 by the looks of it but there is no way we can tell by a photo. Youll have to measure it or try a known thread on it.

Measure the OD with calipers and use a thread checker to check the thread pitch.

This is my guess as well, but I believe this thread pitch is more commonly referred to as the fraction, “5/8x24”, easier to find muzzle adapters and attachments when searching for it this way.

 

[Deerhurst]

Calipers will read.625 for those who do not know what 5/8 is.