Rastus... the CMMG Radially Delayed bolt uses a bolt and barrel extension similar to an AR15...but the bolt has an angle cut (45 degrees ?) to a relatively sharp point, and therefore does not engage the barrel extension with full contact lugs...a slight amount of bolt movement cams it to unlock... the bolt is larger than a 5.56, but the carrier is thinner on the wall, making the entire bolt system have less mass than a 5.56 carrier, and on paper, should have less recoil than a traditional blow back 9mm carbine... the cam action is quicker, so as the rifle recoils the point of the bolt in contact with the extension unlocks and allows the bolt to cycle...I perceive it like an inertia bolt of a Benelli, the bolt momentarily stays in place due to inertia, and the firearm moves around the bolt due to recoil... a cam then unlocks the bolt to cycle
CMMG makes the system with a proprietary lower, and also sell the bolt and barrel singularly... the problem is with the magazine clearance... the magazine geometry built into their proprietary lower is not the same as other blow back lowers...the magazines sit too high in my NFA billet lower, and caused interference problems when hand cycling dummy rounds through it
I found that MagPul Glock mags worked fine, but only came in a 27 round capacity.... a 3D printing company has made a couple of extensions for the PMags... I prefer to shoot the clear ETS mags for competition, so for them I clearance the magazine bodies initially and then remove most of the nose of the follower forward of the feed lips,.... with the rearward motion of the bolt, the very sharp tooth of the bolt lugs would strike the nose of the mag follower as the angle was different... just lowering the magazine catch shelf did not work for me... I got the ETS mags I like to use working finally, but in doing so with the PCC out of action, shot a USPSA match with the stock G17, the first pistol match I've shot in 3 years...I had forgotten how much fun it was to shoot a stock pistol
I put together the Carry Optic as a proof of concept, as I believe that it is the gun of the future, for me at least... I have cataracts forming.... as I most likely stick a Trijicon RMR on the G45 or the extra G17 slide... regards Les