A tight patch is a necessity both for gas seal and to engage the rifling. I suspect some crud in the barrel. A .005 patch should go down way easy and you shouldn't be using it. Too loose. The flames will blow right past through the patch.
Shouldn't be using those in your 50 cal either. A patch should be so tight that the weave of the cloth presses into the lead over the lands and fills the grooves. If you extract a loaded ball with the co2 thingy or compressed air you should be able to see the weave pressed into the lead. Check the bore with a bore light it should shine.
Also .530 + .010 = .54 allright but that is the space between the lands. That does not allow for anything to fill the grooves. Think about it a 30-06 cal bullet measures .308 so that it can engage the grooves and spin.