44 special brass is usually easy to find. For informational purposes, I just weighed 14grains of unique and put it in a starline 44 spc case. Below is what it looks like... pretty hard to miss.
I buy trail boss whenever I can but for me it has been one of the harder to find powders.
You can double charge just about any pistol round, at least with a fast or medium powder, if that's any comfort. It's pretty rare. A squib load is way more common. I cannot think of a single person I know who has double charged a pistol round though, but I can think of plenty of folks who loaded rounds without any powder. The headlamp is your friend.
