I have a.45 flint LR for squirrels and a .54 Hawken that I built for elk and after much range work finding accurate loads for both, haven't noticed any difference in POI between the first shot and subsequent shots w/ a fouled, unswabbed bore.
The difference between a clean and fouled bbl would probably be more apparent in the .45 LR because only head shots are taken on squirrels and I've experienced no difference in POI.
When I used a .50 TC Hawken w/ conicals on elk, a fouled bore kept the conical on the charge...tried some tamped newsprint ahead of the conical w/ a clean bbl but the accuracy went to pot. That's why I built the .54 Hawken and use PRBs.
I don't swab between shots while at the range or while hunting....after the PRBs become hard to load, a bronze wire brush is sent down the bore a couple of times and the debris is dumped. Much easier to load after that.
I consider my MLers {not my builds which are all sold} as tools for hunting and wouldn't own a hunting MLer that req'd a lot of fussing because of poor ignition, poor accuracy if the bore isn't swabbed after each shot and picking the vent after every shot.....Fred