Correct. no breach plug and they make or made 2 style of "nipples". One is called a Flame Thrower and IMO is total garbage. It throws flames alright!!!!!! I dont remember if i tried the musket cap but it should be reliable.
The 54cal is a 1-38 twist
The triggers are very very good for a meat and potatoes rifle. Possibly a real Timney but i cant remember what mine looked like. You are not supposed to remove them from the action according to T/C.
Stick with nipples without the flame thrower label (harder to find now) and the 209 conversions are all FT versions and terrible IMO. LOT and LOTS of blowback with any Flame Thrower but the 209 has a habit of tearing 209 primers apart also.
Keeping the "plug" nipple threads and short passage clean is a must and a bit inconvenient but not impossible. Mine did not look like the entire hole for the nipple was threaded and it gets dirty (obliviously) resulting in hang fires.
Mine shot rounds balls ok with about 80gr of Pyro RS. Not great but still good enough for 50 yard shooting.
435gr Bullshops shot ok too but i forgot the charge. Its my friends load after i sold it to him. I used Maxi Hunters IIRC but its been so long im not sure.
I used to shoot the MMP 54x50 sabot also and a Barnes 275gr Expander MZ with 100gr of T7. Still not great but good enough for sub 10 yard shooting. Shorter bullets should work even better in the slow twist.
Sorry, i cant remember more atm, ive got a few things going on atm.