OK- what does the material measure on a mic? I suspect that .017" is with calipers - I have 3 sets of calipers and they vary .003" depending on the width of the jaws. The largest reading set of calipers is still .002" smaller than my mic. while the rest give up to .005" smaller readings.
Taylor's mic reads .001" smaller than mine, and LB's calipers read the same as my mic. Perhaps he's not squeezing the tines together with his fingers as hard as I am - don't know - but! All I do know in this particular matter, is I don't trust that measurement as true.& For the moment, accepting it as truth and if it is indeed as thick as what I'd call .017", it is at least .004" thinner than I would use with that same ball.
I prefer to use balls that are .005" under bore size with a .0215" to .0225" patch, but do admit to using smaller sized balls in 2 rifles, both having only .008" deep rifling. Both of those guns do well with .0215" and .0225" patches, - wet almost dripping with moisture, not merely spritized with Tracy's leaf moisturizer.
I suspect it's a case of too thin a patch - afterall, given .010" rifling, there is only .002" compression in the bottom of the grooves IF the patch actually measures .017" with .010" rilfing, and if the rifling is .012" deep, the ball and patch are undersized, barely touching the bottom of the grooves.
A .017" patch might work well in that barrel with a bore sized ball orone only a cou-le thou smaller than the bore, but not that little .490" - imho.