Hex drive drill bit as a carbon scraper for the SCAR.
The gas piston is 11mm. The gas cylinder is just a little bigger, so it is a sliding fit. It is a touch over 11.1mm …. which is 7/16″ (11.1125mm). So it seems FN is making the gas cylinders by drilling them with a 7/16″ drill. If the cylinder was drilled with a 7/16″ drill, a 7/16″ drill is about the best carbon scraper you could ask for. So I found a source of drill bits with a 1/4″ hex drive, so you can use my hex driver, or a little ratchet driver for hex bits (screwdriver handle requires an extension, so the handle is beyond the barrel end).
This thing just slides into the cylinder beautifully.
Note, this drill will only scrape the widest section of the gas cylinder. You need separate drills for the other diameters.