2 to 4 thou thicker patch than the mathematically calculated based on ball dia., bore, groove dia. and patch thickness.
One of the tricks I performed to verify the patch thickness I chose to use in my gun, was to slide a 1/2" x 6" brass rod into my clean and lightly oiled barrel then load a patch ball (no powder) to just below flush from the muzzle. Then up-end the gun and shake the gun up and down, the brass rod act like a slide hammer and will hammer out the patched ball.
Now look at the ball in good light with a magnifying glass.
You are looking to see the weave pattern of the patch material pressed into the soft lead of the ball.
You should see the weave pattern pressed in heavy on the lands and lighter at the grooves.
If you don't see any weave marks on the ball at the groove locations then the ball is too small or the patch is too small. The cloth digging into the ball is where the extra 2 to 4 thou are getting used andI believe helps put a good spin via the rifling with out slipping in the rifling.
I prefer to use the biggest ball recommend for the bore size along with a patch thickness tough enough and thick enough to survive the trip down the bore and back out again at speed.
I also bought a small 8 oz. dead blow hammer to start the ball into the muzzle.
I use the hammer much less now that I've learned to use a flat topped short starter and to pound the short starter with the bottom of my TIGHTLY closed fist. At range I use the hammer, in the field my closed fist.
My new GPR cut up patches at first. I cleaned the bore with JB bore shine several times and I believe that accelerated the removal of sharp edges on the rifling.
I also use an over size, over powder felt wad (58cal wad in a 54 cal bore) lubed in melted mink oil grease.
The OP wad greatly improved accuracy and stopped patch burn through during the early patch cutting via sharp rifling time. The OP wad is part of my standard load used on every shot.
