That's odd Magwa. The subs have significantly less energy (more so when firing unsuppressed) so you typically want lighter reciprocating components so it cycles.
Then again who am I to argue since yours works!!
Did you put it together? It's most likely port-size related. You're looking at a 0.095"-0.1" port size with a 10.5" barrel for it to run reliably with subsonics under the worst conditions.
Carbine or pistol length gas system?
Barrel port size?
Buffer weight?
These are the most important factors if you want it to cycle reliably on supers AND subs in all shooting conditions.
That was one of the "touch-ups" that required my attention on my CMMG too. Didn't notice it at first (i.e. out of the box) so I'm wondering if it somehow worked loose......
Trying to picture how the ACP would fit/work on an AR pistol....would a simple quadrail float work just a well on an AR pistol? Is there a feature specific on the ACP that is not achieved with a quadrail float handguard?
Just thinking out loud....
Or tell me what you want on it and I'll build it that way.
That would be interesting.... like an oversized freefloat/quadrail that extends backwards. Love to try making one.