These days, whatever you can find. Get nipples for #11 & musket caps, then grab a bunch when you see them.
Be aware that there are some caps meant for re-enactors that are weak; CCI makes such for muskets, at least. Magnum 11s are good, as are standard musket caps. I bought 1000 RWS from my local BP supplier for my 1858.
Muskets or #11 for the 1858?
I have had a few misfires from CCI musket caps, very few but enough to make me learu of em.
