I just bought a new Uberti 1861 Navy, 36 cal.

What cap size should I use? 10 or 11? I keep hearing both from people. The gun's manual does not specify.

I heard using the wrong cap size can lead to a chain fire, from cap not fitting well on the nipple. Help me make the right choice as I haven't fired the gun yet, and I don't want my first shot to be a chain fire!