Admountainken, I have a .40 caliber with a 38" Rice barrel that occasionaly shoots some pretty tight groups. I built this rifle some 15 years ago and I'm pretty sure it's a 1-48" twist.
I shoot .395 round balls. I've found that using .018 ticking patching the rifle is pretty hard to start the ball, I attribute this to the sharp chamfer at the muzzle. The rifle shoots good with .010 and .015 patching but most of this size are not wove tight enough or tough enough to suit me. In a quest for good .015 patching I ordered some .015 ticking (without stripes) from easternmaine shooting supplies, I bought from their ebay site but they have a regular internet site as well. This was the patching I'd been looking for, good and tight.
Anytime I'm not hunting I use Original LeHigh Valley patch lube when available, now I'm trying Mr. flintlock's patch lube. So far I like the Mr. Flintlocks lube. Thing is with these lubes they load easy, are accurate, and I can shoot all day without cleaning.
After a couple of range sessions with the new .015 patches and Mr. Flintlocks lube it seems my rifle shoots just as well with this combo as with .018 patch and other lube. The .015 is definitely easier to load.
I mostly shoot at 25 yards but I've done a little at 50 also and my old eyes are what determines the group size, not the load. My target load at 25 and 50 yards is goex 3fg, shoots the same at both distances. My turkey load is 60 grains of 3fg and is shoots good also.
Hope this helps a little.
DH