I used musket caps on my 3-band .58-cal. Pattern 1853 Enfield rifle musket for more than 30 years and they never failed to work, but I don't use them on my .50-cal. GPR or Renegade. The No. 11s have never failed me yet in 40 years. Musket caps on a rifle made for No. 11 caps is overkill, but that's just me. As long as my rifles are cleaned properly and lubed, they have always fired 100% of the time with No. 11s. Decent musket caps have gotten hard to find, other than reenactor caps. I still have one tin of German musket caps left I'm hoarding for my Enfield, and I just use it for living history demonstrations these days. Still, you got a great bargain on those caps.
Interestingly, I did the reverse: I bought a TOW nipple that fits my Enfield but uses No. 11 caps, and it works fine with them. I can find No. 11 caps all day cheap at Walmart or Academy.