My Lyman Gpr is a .50 RB shooter and this is what I learned since bying it new back in 1980:
It ate up any store-bought patches no matter what lube I used. Accuracy was dismal. I sent it back to Lyman and they sent it back to me with a 50 yard target showing match quality groups - two groups with the ragged hole thing. They clamped the rifle to do this, thus showing that the quality was pretty good.
They advised me to stop using the store-bought .010" - .015" patches and to use heavy-weight .018" thick pillow ticking. You know, the stuff on old army mattresses. It's like canvass.
They used Crisco. I used Lube 109 (no longer available) and have since used WonderLube when the 109 ran out. Now, MY groups aren't as pretty, I shoot about 2"@50 and about double that @100. But, I have yet to miss a deer or have to shoot a second time because I keep it short and responsible. Yeah, plenty of 'em walk but it's a game not survival.
Took about 500-700 rounds to smooth the bore but the ticking helped the accuracy right off the bat. My advice would be the same as Lyman's: use genuine pillow ticking as tight as you can get it.
Saturate your patches by melting the lube and dipping them before you hit the range. That way you'll better distribute the lube and things'll go smoother when you don't have to fiddle so much at the bench.
After you short-start the bullet, put a dry cleaning patch over the bore and ram the ball along with the cleaning patch. It will come out as you withdraw the rod and you will have a reasonably uniform bore before each shot - all in one motion. At about 7 to 10 shots (or when you start getting flyers) swab with a slightly moistened patch and follow to dry.
As to your volume of charge, well, it seems that 70 or 80 grains should do nicely. I have nothing to add except that Crow-feather says to use 3F and I agree. But, on a .54... I don't know... 3F seems to foul less and burn more completely. Can't explain it.
Cleaning: Ya gotta clean thoroughly. You can do it different ways - bore cleaner on a swab or hot soapy water, but it has to be thorough. Myself, I used to use the swab but now it's hot soapy water everytime unless I'm in camp and I'm due to head home soon. Then, I'll soap 'er out when I get there. Heats up the barrel and opens the molecules so the junk comes out and the oil goes in. Lemon oil on the wood, good gun oil inside and carnauba wax on the outside. Incidently, my GPR and Dixie Tennessee Rifle look very authentic because they've been rubbed and shot and handled so much that there's little finish left on them. But, the bores are lovely...
The sights: I have to say that I have never been a fan of the huge sights on the GPR. Must be a foot wide up front and not wide enough in back. I filed the notch wider and more square but it's hard to draw a fine bead, so to speak. Maybe, after all these years I'll make a change...
Hope some of this stuff helps. Keep trying and let us all know.
