For hunting shotguns, once or twice a hunting season. My Benelli SBE will throw a couple thousand shells a year and I'll just clean the bolt a couple of times. A wipe down after it gets wet. If you like doing it, it can't hurt anything!

I'd clean the EX's Beretta 303 semi-auto after a couple trap shooting tourneys. Prob 2-4000 rounds per cleaning. If it was a Model 1100 every 500 rounds. Break guns, just clean and re-lube the hinges every few thousand.
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..."the clock looked at me just like the devil in disguise"...