If it came with top hats, that is a old term to describe musket caps. The difference between the two, a #11 is much smaller, would never fit on a musket nipple, and it has no brim on the bottom. The musket cap looks like a tiny hat.

Since your using pellets and musket caps, you might have some ignition problems, but only range time will tell. Actually if I were shooting pellets I would want a 209 breech plug in there.

777 is safe to use, as is Pyrodex RS. Just never put any smokeless powder in that rifle is all. Those Shockwaves might shoot just fine. All you can do is try. Be sure to swab between shots with a moist patch. Work it in short strokes down the barrel and back up a couple times.

If you do have ignition problems, go out and get a jug of Pyrodex RS loose or 777 2f loose powder. Then you will have no problems. Pellets are a little hard to ignite which is why the 209 shotgun primers are used.

If you want the whole scoop on that rifle get a hold of Sabotloader. He has a couple and can tell you all about the rifle, what it likes, dislikes, etc..