The only fouling that is normal is a dark carbon build up. If you keep the upper slightly lubed with CLP, then it will break down the fouling and allow the working gas pressure to blow the crap out of the rifle.
From the start, the bearing surfaces of the rifle should be lubed, then after a few hundred rounds; a few drops of CLP should be added to the carrier gas ports on a slightly cocked action. This will allow the CLP to get back to the carrier gas chamber, and the working pressure of the cycling action will move the lube through out the rest of the action.
Now if your getting a lot of brass flakes fouling, then you will need to clean up a few areas on the rifle.
The extractor claw ends and relief channel ends for the case rim.
The feed ramps on the barrel extension (end cut burs).
The ejector opening on the bolt face.
The underside of the feed lips on the mags, and the front leading edge where the round climbs out.
Any burs on these areas will lead to the case being scraped on loading or recharging, and these flakes will find there way back into both the bolt and the action, which a fresh coat of CLP will not resolve.