Sorry, Hawg, but if he's using Remington No. 11's, going to Remington No. 10's doesn't mean he'll be getting a smaller cap. It MAY (or may not) fit further down the cone, and thus appear to be a better fit, but it's not smaller.
Cap size numbers are utterly and totally meaningless. Once again, here's the data, measured from at least 20 samples of each brand and 'size':
Remington No. 10's are not the same size as CCI No. 10's, nor are the No. 11's the same size. Furthermore, Remington No. 11's are actually smaller than Remington No. 10's.
To make things even more interesting, there's absolutely no standardization in the size of the nipple cone that the cap fits on.
Finding the right size cap is essentially a crap shoot. You can dress the nipple cone to fit whatever brand and size of caps you happen to have on hand, but you don't get 3 decimal place precision for 4 cents in today's world, so good luck on the next batch being the same size.