Hi Stan in SC,
If your 54 is half as good as my 50 New Englander, you won't be sorry for your purchase. (If you do decide you're sorry, drop me a note and I'll probably buy it from you!)
Anyway, trying different bullets could be fun I suppose. Some of the specialty bullets can get kind of expensive though.
Roundball is cheap and, at least in my 50, phenomenally accurate. A couple of weeks ago, I put a three shot group at 75 yards into one of those yellow post-its...(the office pad thingies), benchrested.
The only thing I can probably tell you is that, with roundball, my 50 likes 70 to 80 grains of Goex FFg. Higher or lower and accuracy falls off. It likes a specific patch thickness....075... a couple of thousandths more or less and accuracy falls off. (The Ox-Yoke prelubed .015 precut patches should get you pretty fair accuracy with your rifle if you're not up to making your own patches.) Lube slickness is likewise critical. However, if you do find the "magic combination", it should be a tack driver.
Also, I cast the Lee REAL conicals , 320 grains, for my 50. I shot a 7/8", 3 shot group at 60 yards on Saturday afternoon with 82 grains of Goex FFg, benchrested.
Your rifle should do likewise with RB or conicals. Sabots... sorry, but I don't know. I've never tried sabots. Since they're expensive and I cast for next-to-nothing, it's probably best that I don't find out if sabots are too good!
Good luck,
Jerry.