OK, more details. I'm using Neatsfoot oil for lube, quite wet. My patches are .012" so if you use a .437 ball, that equals .449 of things filling the bore. It's a Colerain, and measures .443 across the lands.
I'll shoot a few on target next, and look at the patches too.
From your numbers, you have a .467" at .012" deep rifling, or .463" rifling at .010" deep rifling.
Your ball and patch combination is .437" + .012 + .012 = .461", thus, even with only .010" deep rifling, you are short of filling the grooves, thus likely have blow-past which fouls the bore, especially
at the breech.
What do your recovered patches look like?
Can you find recovered patches?
Browns streaks out from the black marks is blow-by.
Simple holes from the lands means you are likely cutting the patch from too-sharp a muzzle crown. With that, I would suggest you search for muzzle crowning threads.
Burnt large holes is from blow-by destroying the patch. Charred shreds says the same thing.
I have never used such a poor (thin) patch. The thinnest patch I will use, is 8 ounce denim that I measure compressed at .019" to .020" & that is with a bore sized ball.(same as the bore diameter).
I was using a .360" ball in my .36 Rice barrel, with a 10 ounce denim patch (.021" compressed) until I ran out of them. Now, I'm back to using .350", with the same patch.
With your combination being difficult to start, that sounds as if the crown is too sharp. Then it loads fairly easy until it does down to where the fouling has accumulated.
Solution, is a re-crown and thicker patch as with at least an 8 ounce denim. You are using a starter, which is good.