I tested my .69 Sporting Rifle to 200gr. 2F GOEX, receiving increased velocities with each additional increased powder charge.
At 165gr.,(6drams) I recorded 1,550fps with a 480gr. .682" round ball patched in 12 ounce denim. At 200gr., I recorded 1,700fps.
I accidentally double charged my standard hunting load of 165gr., and recorded only 1,770fps for that 330gr. of 2F, thus I assume
my GRRW barrel has fired a few "proof" loads. The patches, incidentally, are reusable with the addition of more lube.
I did not have to "swab" the bore at any time during the testing, or at any time while shooting this rifle. Accuracy was unchanged,
BTW, from 140gr. to 200gr. in bench shooting. Using 165gr. 2F, this rifle has produced 1" to 1 1/2", 3 and 5-shot groups at 100 yards,
off the bench. That was my moose load as it matched "Forsyth's" 14 bore drop charts over 100yards distance.
I found in the Lyman BP handbook, a co-relation between velocity and pressure. This means that to produce a certain velocity, requires
a certain pressure using the same grade of powder, but in different bore sizes. By this, I mean that a .50 cal producing 1,700fps with 'X'
grains of 'Y' powder generates 'M' pressure.
A .58 or .60, producing 1,700fps using "Y" powder, generates that same "M" pressure, just as a .69 or .72 making the same velocity with
the same 'grade' powder is generating the same "M" pressure.
Recoil, of course, goes up quite exponentially, however some stock designs are better able to handle it (English and German come to mind).