My 15-22 is Always the dirtiest gun i bring home after a day at the range.
Mainly the bolt, Which i take the spring and guide assembly apart to get that fully clean.
I have a bad and i mean BAD habit of over lubing all my guns. Thats not a bad thing until it comes cleaning time.
But in reality the only thing that needs lube internally is the guide rails.
I just bought a CZ Ultra Lux and it stays so clean i thought something was wrong. After 300 rounds you can brush the bore with hoppe's 9 and then run a patch and it barely has smudges on it. And only the bolt face gets a little dusty with burnt powder. Being a bolt action helps as does a well lapped barrel and tight tolerances.
I shoot the same ammo threw both guns, Its the design that makes the difference and not the ammo. My 15-22 has never come home lightly dirty its always caked in residue.