I've shot 777 ffg in my sidelocks for years. Pyrodex will ignite better probably but I've never had a problem getting 777 to go off and I like how it cleans up better and is more powerful so I stick with that. I just use CCI Mag #11s without any problem. Your musket caps should more than do the trick. As Cayguad says, the key is preparing the nipple and the bore.