In school I shot competitive rimfire with valuable Anschutz .22LR rifles. Our team didn't clean our rifles until the end of the season, even though we fired thousands of rounds through them during practice and competition. The problem with cleaning is that it takes barrels some number of "fouling" shots before they reach some equilibrium where peak shot-to-shot accuracy is attained.
Granted, this practice of not cleaning during the season may have been facilitated by the following features that won't be present in field use:
- The rifles were always stored in-doors and never exposed to excessive moisture. During the season they were shot regularly, so any moisture that might have condensed in storage would not have sat long before getting worked or cooked off.
- The rifles were bolt action.
- We only shot high-grade target/match ammunition (usually Eley).
Subsonic rimfires shot with properly lubricated bullets are unique in that their barrels don't accumulate copper or lead fouling like barrels that shoot higher-velocity bullets under higher pressures. Therefore I am only aware of four reasons to clean them:
- Their actions get so gummed up that they experience feeding malfunctions.
- They have been or might be exposed to moisture for an extended period, in which case all steel needs its protective coating of oil refreshed.
- They have been in storage and their condition is unknown.
- They have been fired with questionable ammunition that might have left lead fouling in the bore, or a squib has to be knocked out of the barrel with a cleaning rod.