COLT 6940 AR 15 CAN BE FUN FOR ANYONE

I'll try out to search for some. The piston rings look like the bolt rings but at more compact. The outer diameter is about .375 of the inch as well as the internal diameter about .310 of the inch.I wasn't able to find anything about this, are you able to connection a source? I did locate an posting with regard to the 6940 blowing the facet out of