I clean my bore every 4th or 5th time out weather they need them or not
that said... you want to talk fouled bore... my buddies & I used to get together on weekends ( several years ago ) & shoot dueling trees with 22 auto hand guns of various ages.... the trees were mine, as was the range, so often I shot with one group on Saturday, & another on Sunday, & would normally clean during the week, sometime after... I usually shot copper washed Federal bulk packs, but one day, the local store was out, & I'd shot a lot that month, & funds were low, so I bought 4 bricks of Remington Thunderbolts... I didn't know it at the time, but it was a set up for disaster... Saturday came, & I shot 600-700 rounds, Sunday came, & somewhere over 500 rounds, I started missing... the more I shot, the next couple 100 rounds the gun went to heck, & I couldn't hit the broad side of a barn...
went to clean the gun up, on Sunday, & found I had so much lead in the bore, that I got a 22 caliber bore brush hopelessly stuck in the barrel... I took it too my buddy ( retired gun smith ) who was able to use his bench vice to press the brush out, after a liberal soaking with Kroil... along with the brush, along came about 3 bullets worth of lead the brush chased out of the bore...
from that day on, I swore off Thunderbolts... though it was just as likely the bore was fouled with copper, before I started shooting lead...
anyway, to this day, I always like to run a wet patch of Kroil down the bore, followed by a dry patch, before I go out & shoot... I find just a couple patches down the bore, & some rifles I can't tell you how many rounds have been down the barrel since it had a brush in it...