It is my understanding ..... that lead is a "natural" lubricant. Many .22 rimfire manufacturers coat lead bullets with wax or grease based lubes. Others use a copper wash. 22's operate at relatively low bore temperatures and pressures. Consequently, lead build-up in the bore is much slower than the copper fouling seen in high pressure/temperature centerfires. Carbon can build up in the "throat" area. At least, that is what I think
Good advice would be to run an oil patch after every outing. Personally, I clean the bore if the rifle will sit for an extended period...using a combination of lead and carbon "solvents".
When testing various brands of .22 ammo, I either clean between change-overs or shoot at least ten shots with the "new" stuff before assssing performance. It is my belief that it is necessary to purge the "old" lube type before getting serious about laying down a bore coating with "new" lube. ie: between wax lubed bullets and grease lubed bullets. Hope this makes sense.