The one drawback of the AR-15’s direct impingement gas system is that it leaves a nice amount of carbon fouling in every imaginable crevice inside the rifle. Given enough time and enough neglect, the rifle will start to malfunction due to excessive carbon buildup. For the most part, cleaning the rifle is a straightforward affair with just a few rags, patches, solvent and a cleaning rod. However, the inside the bolt carrier, where the back of the bolt meets the carrier, can build up an excessive amount of carbon since that’s it sits right behind the gas rings.
The GM-223ST is designed to fit down the bolt carrier and scrape away all of the excess carbon buildup. Instead of wedging patches soaked in solvent down and then trying to push them back out, the GM-223ST loosens up all the carbon so it will simply flake out when turned over and tapped. It makes cleaning the bolt and carrier a much less lengthy affair.