I'd love to see a video of you loading a GPR with the .022 patch/.535 ball Daryl.
Just to satisfy my curiosity.
Loading their .54's with that combo is what 3 guys who shoot .54's on our trail do every time they shoot. Oops, except Len that is. He uses the thicker Railroad mattress ticking we measured at .0235", with a .535' ball.
I don't have a GPR and neither do any of the guys who shoot with us now, so cannot make that video. I use that same combination (.005"undersize and .022") of ball and patch, in my .36 & .50. I did use it in my .32 ?? barrel, .40 Goodoien and .45 GM barrels, but I sold those rifles. Too, in the Goodoien barrel, the ball was actually .398", same measurement as the bore, so I was loading a bore sized ball in it along with the .022" patch, but also the .0235" patch until I sold it. That barrel had wide grooves, making loading very easy. My .69 likes the .682" ball of 482gr. and a .030" patch with no gas leakage up to 200gr. 2F. The patches are re-usable. It also shoots well with the .677" WW ball or .675" pure lead ball and the 14 ounce denim patch I measure at .034". Those patches are also reusable.
In the .36, I am currently using my remainder of the .0235" patches and a .350" ball. The barrel is a Rice, flat bottomed at .010" deep. Thus the groove to groove is .380" Those patches + ball dia. runs .397", .017" larger than the groove diameter. I showed Taylor I loaded the ball 1/4" down into the bore by just pushing on it with the short peg on my short starter, then one smack, now it went 6", then the rifle's rod down to the powder - 2 FINGERS only on the rod - yes - I had to squeeze the rod with my fingers, but - needed only those two- index and middle finger.
Just about every day we shoot the trail, someone will mention the thin patches many of the guys on this forum use & need to wipe the bores due to hard loading. We find that more than quite interesting, actually. Have you guys read Ned Robert's book, "The Muzzle Loading Cap Lock Rifle"? I bought my copy in 1972 & studied it. Mind you, it took me 2 or 3 years to figure out the re-crowning and use of .022" denim for patches so, as Ned wrote the Dutchman said " ven you loads der next vun, you cleans der last vun". To me, that meant it needed some compression in the bottom of the grooves to be snug enough to do it's job. He was right - it works.
Since a lot of the guys here never take their barrels off to clean them, sometimes I wonder how many of those barrels actually get clean. As well, how many of those barrels have shot Pyrodex or other perchlorate or chlorate powders? A rough bore will certainly hold fouling. We, none of us here, EVER have trouble with fouling & we all take the barrels off our rifles, even the long rifles, for cleaning. Water is sucked in and pumped out until they are clean, then dried, then flushed with a water displacing lubricant, then excess wiped out again and oiled.