.490" is .010" less than .500". ie: 10 thousandths smaller, not 100 thousandths smaller, as in .1". A small difference on paper but a huge difference in actual measurement. 100 times different. It is a common mistake and many of us, me included, have made it - right here. The reason your math seems to work, is the .0's zero is missing in all your figures.
Rice .50"- we'll assume it's a true .5" bore and they usually have .016" rifling, so: .500bore + .016rifling + .016rifling = .532"- groove to groove.
A .490" ball + .024"patch + .024"patch = .538" - .532" = .006" total compression divided by 2 (2 sides) = .003" compression in the bottom of the grooves - each groove.
This load, we know, loads quite easily and might show good accuracy as well, with moderate loads. However, .003" compression might not be enough compression for heavy hunting loads and might show burn throughs or burnups with them. A .495" ball will increase the compression slightly and improve this fit.
As to patches being reusable, they should be. You should be able to pick up a fired patch, re-lube it and use it again - perhaps up to 5 times - then, you'll know it's a good one. I've done this 'test' and showed exactly the same accuracy as with 5 new patches.
We have guys here who use .490" balls and .012" patches and claim "good" accuracy - so - whatever anyone is happy with is good by me, from now due to LB's 'directive'.