WHAT DOES COLT COMBAT UNIT RAIL GUN 45 MEAN?

I've RIA drawings specifing barrel markings on a completely new USGI rifle Which marking will not be approved.If it is a bell shape, that will be proper for the Colt. And also the gas tube coloration and texture is exciting. See When the gas tube will draw in a magnet and also to what diploma.     All the rest of the areas I see are Colt.     �