sleddog,
I was just gonna mention what you & Pruson said in your last posts.
It isn't so much in the powder fouling, as it is in the copper fouling. Also, the smaller the bore diameter, the worse, or quicker you see the deterioration in accuracy from copper fouling, mainly.
In other words, a .308 might shoot longer dirty, with decent accuracy, than say, a .223. My hunting partner has his .17 Rem. that he has spent plenty of bench time with. He has mentioned more than once that using regular jacketed bullets, he can't go more than 20rnds. before accuracy drops off noticeably. Since he switched to using moly's in it, he can go 50 or so, before it needs a scrubbing. If you're shooting over a chronograph, you'll also see velocities start climbing as bore fouling becomes worse. ES and SD numbers also appear to fluctuate from string to string as more shots are fired, seemingly indicating that fouling is having an affect on the load somewhat.
Pruson...
Since you mentioned the .204, I'm working up loads for my father in law's Ruger now, and it's the same as you mentioned. After 20-30rnds., if you don't clean it, you start getting fliers. Once cleaned, with a couple of foulers, it returns to what it was. This is a critical observation when building loads for a gun.
I like shooting those tiny little groups just like the next guy. But, even though, as a general rule, a gun might shoot it's "best" groups when it's cleaned, with a fouling shot for good measure, realistically, hunting accuracy doesn't have to be benchrest quality.
Some guns might shoot 1/2" groups following a good cleaning, and after a good number of shots, only shoot 3/4 to 1" and stay put at that point throughout. If it's acceptible to you & your hunting needs, so be it.
Who's to judge otherwise ?
Doing load testing, or range work, I like to clean my guns every 30-50rnds as a rule. But, once my guns and loads are "tuned", I might go a whole season of hunting before I thoroughly clean the gun. A wet swab of the bore, followed by dry patching, is sometimes done mid-term though. And if I have to re-check a scopes zero, I'll do a total clean at that time. But that's a rarity.
Mainly, I like my guns clean, as "I believe" it allows the best chance for accuracy, and that if done correctly, it allows a longer accurate barrel life.
But, that being said, it's a "to each his own" situation really, and what is acceptable to the individual.
Take care,
Bob