Metric thread pitch AR barrel question

Sarge_DL

Sarge_DL

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Finally decided to build the Heinz 57 Mutt gun from all the leftover parts that I have collected over time. I was gifted an old 20" AR15 barrel years ago. No markings on it. I'm pretty sure it is Chinese. Some of the very first Norc ARs that came into Canada had the metric threads I was told. I'm wondering if anyone knows the metric thread pitch off the top of their head. I don't have the thread gauge tools yet. My standard 1/2x28 A2 bird cage slides over top (just barley). I'm guessing it's maybe M13x1?

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Can't say I ever heard of a AR with a metric thread pitch for the muzzle.

Only one that uses a 13x1 is a Steyr Aug and its LH pitch.

Maybe someone threaded a 1/2-36 FH and removed the threads?
 
M13x1 (.5118 x 25.4) would be larger diameter than 1/2-28 (.500 x 28), so it definitely wouldn't thread over top.

I know that M305 had metric threads.....but I've never heard of a Norc Ar15 having metric threads.

You're saying you can't thread the flashider over it? or you haven't really tried?
 
The threads look like they’re in good shape. I was putting on the A2 bird cage and it just slipped all the way on. I’ll get a better pic of them tonight.


edit: Here is a pic. The AR barrel is on the left and my Walther PPQ Navy on the right. The PPQ is verified 1/2x28. I'm not sure if the picture will show that well but the AR's threads are father apart than the PPQ:

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Likely M12 x 1.25

That would make the major diameter of the barrel .472" and the standard flash hider would be .464" minor diameter.
Allowing for wear and thread tolerances it might be possible to barely fit over. I don't have machinery's handbook in front of me to check the math of the tolerances.

The pic of the 1/2-28 thread next to the barrel visually appears to be a smaller pitch, which makes sense.
 
Man, that must be a huge pain in the ####. Good luck finding a muzzle device with threads that will match.

I ran into a problem with a Norc A1 lower I have, trying to find a grip screw, which happens to be metric.
 
shhh said:
Likely M12 x 1.25

That would make the major diameter of the barrel .472" and the standard flash hider would be .464" minor diameter.
Allowing for wear and thread tolerances it might be possible to barely fit over. I don't have machinery's handbook in front of me to check the math of the tolerances.

The pic of the 1/2-28 thread next to the barrel visually appears to be a smaller pitch, which makes sense.
Click to expand...

Looks too fine to be x1.25, Maybe X 1.0
 
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