BE AWARE …
Background - Last year a greased wad, aka 'lube cookie' worked well for XX to minimize any BP build up when placed over the powder and under his roundball load, allowing multiple shots without cleaning in-between shots.
Problem - This year, XX noticed that the accuracy was off and he restored it by eliminating the wad/cookie. Otherwise, same power, same charge, same lube, same patch material, same roundballs ... , yada yada … and same 'nut' behind the trigger.
Cause - My guess (actually, ‘learned’ knowledge!) … TOO MUCH LUBE in the bore!
Actual Case Study - Before I got into flintlocks, I had a 'Mowrey' box-lock percussion 50-cal target rifle made by Bill Mowrey of Olney, TX. It was an incredibly accurate BP rifle and I once (while benched at 50-yards) put 4-shots into the same hole the size of a dime! My Father was shooting with me and he didn't believe me ... so I held a tad low and that 5th shot hit 1/2" below the rest of the group. Well my Father became a believer in that rifle and load! In me too, haha!
I was using ... hack, ack, ugghhh ... 'bore butter' (BB) as the lube at that time. Next time out ... accuracy wasn't 'as good' and the next time out ... it absolutely SUCKED! Well I did some researching online on these Muzzleloading Forum and then 'StumpKiller' here from NY suggested that TOO MUCH lube was building up in the bore, or being used, and that the patch was no longer effectively grabbing the rifling, that it was just 'sliding' down the barrel.
Now also recall that waaaaay back then, the BB instructions talked about 'seasoning the bore' (well, it ain't no freaking cast iron pan, in that ‘steel’ barrel!) so that even after one had a clean rifle, to generously coat the entire bore with BB, which I did. Well I'd go to the range, run a BB patch down the ‘seasoned’ bore (why????) before shooting and would then load and shoot with MORE BB on the patch. I probably got to the point where I thought that 'more was better'! But read on my friends ...
The cure? - Try this! - Well I cleaned and scrubbed that bore out really, really well using HOT water to dissolve the BB and scrubs with J&B Bore Paste. Once clean, I only stored the bore by using one patch with Birchwood Casey's Shield (now called 'Barricade') protectant on it, a liquid 'wax' that has never given me any issues in any BP arm. Lo' and behold the accuracy was restored! I continued to use that rifle and BB, albeit sparingly, until I bought a flintlock, caught the bug and sold my 'cap' guns.
XX - Guess what? He too cleaned out that rifle's bore out with HOT water and got it squeaky 'as new' clean, then tried his loads again with wad/cookie and lube patch, albeit sparingly applied. It worked, accuracy restored!
Closing Question - Hmmmm ... I wonder how many guys sold off rifles they once thought were 'shot out', but really just due to too much lube build-up or use in the bore?