The WA GBBR system is one of the major systems as employed by both there own and G&P WOC gas blowback M4 rifles. They make use of full bolt groups very similar to the real thing which includes a bolt carrier. This component can be made of a variety fo different materials.
While steel bolt carriers add mass and thus more kick, lighter Aluminium bolts do the opposite. The benefit form a lighter carrier is that your weapon will cycle a little faster and require less gas to do so.
This model is one piece Aluminium with a semi-gloss (low friction) finish and a while logo on the exposed portion of the bolt. O