G'day blokes. I was chatting to a mate who shoots an Anschutz in our benchrest competition (I use a CZ), he said that Anschutz suggests that (I've used the AI answer) "Anschutz .22 LR rifle should generally have its action and chamber cleaned every 200–500 rounds to prevent functioning issues, while the bore should be deep-cleaned, using a proper cleaning rod and bore guide, every 500–1,000 rounds or when accuracy degrades." he tends to leave the cleaning to 1000 rounds the dreaded 'carbon ring' builds up in some chambers faster than others. My S&W 17 will show a buildup of carbon(?) after a few matches, however, not all of the chambers in the cylinder show the same degree of fouling build-up. Could some chambers be a bit tighter than others?
If you see the buildup at the bottom of the chamber first, thats most probably gravity or some gas + unburnt powder and carbon is leaking back under the case. Did the pressure of firing (23-25 thousand PSI) expand the case to seal the chamber and stop gas leaking back and starting a carbon build up? I really don't see this as a problem if you clean the gun after a session/match at the range with a pull through or bore snake (it's an army thing), I run a dry brush through the barrel and dry patch at home. Shock-horror, sometimes I leave this to the next day... My favorite gun cleaning products are Hoppe's #9 and Mill spec Break Free CLP and good clean brushes. Frequent cleaning won't wear your gun out but it will prevent carbon buildup.