Loose 777 will work fine with musket or #11 Caps. Hodgdon only recommends using 209 primers with the pellets - and it's probably best to heed that recommendation. I had a few problems using #11s with Pyro pellets and they have that coating of black powder on them to improve ignition while the 777 pellets do not.

Loose Powder IS much cheaper to shoot and it allows you to customize your loads down to 5gr increments while pellets can only give you 10gr differences at best. And to be honest, with the use of speedloaders, you can load loose powder just as fast as pellets. Pellets MIGHT be a little less prone to picking up moisture - but that advantage is probably over-ridden by the fact that they can also crumble some too in storage........making your loads more inconsistent.

If you use loose 777, remember it is more powerful than the pellets...................so to get a similiar result as your 100gr pellet load, you need to start working up from 80gr of loose 777 in 5gr increments. And 120gr of loose 777 is to be considered a magnum load - don't exceed that.