[metroplex]

I could have sworn I saw a post from STL a long time ago where he mentioned a certain range for the proper clearance between the muzzle device and receiver in order to allow proper function (for the delayed blowback/recoiling and movement of the barrel).

I measured my stock PS90 to be 0.015" and now with the CMMG 10.4", it's 0.0095" It still rotates and moves freely, but I thought there was a recommended spec. Has anyone come across this as well?

 

[HibikiR]

Huntertown Arms PS90 Shroud question - shroud to receiver gap | FN Herstal Firearms (fnforum.net)

Here's the best I could find regarding measurements, specifically post 5.

 

[Milspec]

Is anyone using rocksett on the adapter or CMMG muzzle device? I seem to think torquing it to 30-33 ft lbs would be enough. On the front end there is no way an adapter or CMMG MD is going to rotate off. If I'm not mistaken the front of the receiver mates with the flats on either device which stops it from turning. On the chamber end of the barrel there shouldn't be any twisting force to unscrew it.

Now I could see using a little rocksett on a MD that is attached to an adapter but not the adapter itself.

 

[metroplex]

Huntertown Arms PS90 Shroud question - shroud to receiver gap | FN Herstal Firearms (fnforum.net)

Here's the best I could find regarding measurements, specifically post 5.

Thanks, looks like Mark from TROS was seeing 0.020 to 0.030 inches. That's quite a bit compared to what I have. Looks like my caliper wasn't calibrated. The PS90 SBR with GSL Gemtech adapter is 0.012"

 

[metroplex]

Is anyone using rocksett on the adapter or CMMG muzzle device? I seem to think torquing it to 30-33 ft lbs would be enough. On the front end there is no way an adapter or CMMG MD is going to rotate off. If I'm not mistaken the front of the receiver mates with the flats on either device which stops it from turning. On the chamber end of the barrel there shouldn't be any twisting force to unscrew it.

Now I could see using a little rocksett on a MD that is attached to an adapter but not the adapter itself.

The armorer's manual doesn't recommend/state to use anything. Just torque 40-50 N-m or 29-37 ft-lb. I normally go 20-30 ft-lb with muzzle devices on rifles. I have found the Europeans seem to prefer LH threaded muzzle devices, my guess is the right-hand rifling twist and spin direction of the bullet causes a LH-threaded muzzle device to not loosen like a RH threaded muzzle device. Same goes for Glock OEM metric threaded pistols (the OG, Glock now sells 1/2-28 RH threaded OEM barrels).

But overall I am not using anything. Blue threadlocker/242 probably isn't going to last or handle the heat. Red threadlocker is a bit too permanent. I may use a drop of Rocksett on the 1/2-28 CMMG adapter threads for a suppressor host/mount.

 

[Jonnyrngo]

I just measured mine after cleaning and I have .018 clearance. I am using the cmmg barrel and GSL technologies bi-lug flash suppressor.

 

[metroplex]

I just measured mine after cleaning and I have .018 clearance. I am using the cmmg barrel and GSL technologies bi-lug flash suppressor.

Do you have any issues with certain types of ammo or when suppressed?

 

[Jonnyrngo]

Do you have any issues with certain types of ammo or when suppressed?

The only ammunition I’ve had a problem with is Detroit Ammunition’s subsonics and I believe it is because their reloads no longer have the coating on the casing. They feel very rough and dry. Suppressed or unsuppressed this is the only ammo with problems that I’ve run. I’ve run all types of FN ammo and American eagle without issue, waiting to try out AAC.