Only in a couple guns did I have any real issues with #11's not setting off a charge but thought I would see how it would work. Sometimes it can be hard to find them, the 209's seem to be easier to find.
I have a musket nipple on a CVA Bobcat. Went this week to a local gun shop to pick some musket caps. He was out and said he has had a hard time getting them he also he was having a hard time getting #11's.
Man that Bobcat gets your attention with a maxi ball and a good charge.