Your Browser is Outdated
The CMMG 10mm Barrel And Bcg Kit is designed to work exclusively with CMMG Mk10 Lower Receivers. You can use any AR pattern barrel; however, you must ensure you have the CMMG BCG with the correct bolt for the caliber you intend to use, as well as a MK10 lower receiver.
Yes it is a proprietary setup. The BCG is designed to mate with the Barrel to deliver the Radial Delay Blowback feature. A different barrel will have different lugs (such as those for direct blowback)
Yes, the barrel and bolt are a "set". You can put them in any upper receiver, and pin to any lower receiver but the barrel extension and bolt are proprietary.