Cmmg has been know to not have good threads on them. I am sure TROS got the threading right on the barrel. As far as tapering your guess would be as good as mine. If I were to run a dedicated flash hider I would just drop the coin on a fh oem part. my 2c

 

Cmmg has been know to not have good threads on them.

This is the first, hearing this.

I have a CMMG hider on my SBR. The barrel floats in the reciever, not supposed to be tightened down to it.

It's supposed to bottom out on the barrel. I don't recall it being tapered though, being metric and all.

 

If they were tapered ( just like NPT ? ) you should be able to see it / measure it with some Vernier calipers using the top jaws and measuring the minor diameter on the threads in the FH .
Not easy to explain but could be checked at both ends of the threads. I just couldn't see the design application of a tapered thread on such a component but could see the use of a starting tap and someone in the manufacturing process not setting up a bottoming tap to finish a uniform thread depth .

 

I'm sure the TROS threads are cut perfectly as the adaptor screws all the way on by hand with ZERO drag.

Also, IF the 16.1" PS90 barrels uses the same threads on it as the P90 barrel, it will not screw on the PS90 barrel where the shroud attaches.

I'll check the threads with my Starrett tonight to see if it tapers, it will start a couple of turns by hand but then gets DAMN TIGHT.

 

Both TROS and CMMG say they thread to M12x1 LH, like the original p90 barrel, right? So I agree that someone's threads are out of spec. Since the TROS adapter works, I think it's the CMMG FH. I'd go to a hardware store and find a 12M metric bolt to screw on to the CMMG FH. If it doesn't fit, you can try to send it back to CMMG for rethreading, or you could just use a $10 threading tap to finish cutting the thread and remove the taper.

 

He is talking about my Rifle here....thanks Pursuit-

ANd thanks Tros for getting the barrel done so quickly...just has the adapter on it at the moment, but would love to get the flash hider put on! Will see if I can find a M12x1LH Tap.

 

They might be a little more than $10.
If you want ...I will check at work for a good one ? ( PM me if so... I would be more than willing to help out )
We are a German company heavy " metric " influence with Tooling Standards ect... so we may have 1 I could loan to you ?
OR Mark at TROS may be able to help also ???

Even if they are not tapered... the major/minor diameter differences would do it... that is generally considered the " class of fit " which is represented by a " D # " designation on metric taps. It is an H on standard taps.

 

I meant to say cmmg has had a bad run in barrels not being concentric, bores off axis .. thats all.

 

Haven't heard anything about this in regards to PS90 barrel's.

 

Good luck! Fixable, but I'm sure it's frustrating.

 

Any update on this?

 

A call is in order.

Correct reference on machining metric thread forms and class of fit follows.

Metric Threads

 

Keep in mind, it wouldn't fit on the threads of the Factory PS90 barrel!

The 10.4" barrel shortened by Mark of TROS had PERFECT threads and his Metric to U.S. Thread adaptor went on with my fingers.

The CMMG flash suppressor would just start onto the threads and get REAL TIGHT!

TROS is going to chase the threads on the CMMG.