I don't think that a .22 rimfire will ever really "break-in". Between the low velocity (1100fps +/-100fps), soft all lead bullets, tiny powder charges and low pressure, you could shoot 50,000 rounds before you'd see any measurable difference in the bore. One thing it will do is get a bit of lead wash in the barrel. This is not necessarily a bad thing, as all the .22LR's I've owned shoot better dirty. The worst mistake I ever made was cleaning my 10/22. I've had it for at least 10 years at the time and it'd never had the bore cleaned after at least 15000 rounds. One day I got the wild hair to give it a thourough bore cleaning, so I scrubbed the crap out of it until it met my definition of "clean" for a CF rifle. Well, the nest time I shot it it was all over the paper. It had consistantly shot about 1.5" at 50 yards. Post cleaning it was like 5-6" at 50 yards. It took almost an entire brick of ammo before it got back to where it was before. The bore's never been cleaned since!

Don't sweat it. Break in is something that MIGHT be beneficial for some high-powered CF rifle barrels, and that is a subject of vigorous debate and the benefits are highly subjective. Just shoot your rifle and have fun with it. Keep the action clean for sure, and clean the bore if you are so inclined.

Mike