Ok, I am new here but have been around some very interesting guns through my life. I realize this gun isn't the same as most have here, so if not allowed please let me know. 

I am currently building a muzzleloader from an original barrel that was relined to a 30 cal with 1:24 twist. The grove depth is .304 according to my calipers. Have been running calculations on a few different stability programs and have found a .65 length bullet is about the only decent option with the slw twist of this barrel. 

Thanks for any and all help here,
Mike

Greenhill says that a .308" bullet in a 24" twist barrrel has a maximum length .593; my estimate is ~105 grains.
My experiments with BP in any .30 CR failed miserably, with gobs of inaccuracy and lotsa cleaning.
I don't know of, never read of great success of .30 BP; I think that the <.32 ctgs were most accurately shot with smokeless. Maybe even .32 and .35.
PP in a .30, muzzle loaded,  24" twist, 105 gr. bullet seems like a recipe for failure to me.

Joe,
Have to disagree. My fast twist 30-20, while delicate, is my most accurate BP short range match rifle. In essence, a 32-20 with a .308 barrel.
Certainly not a 'miserable failure'.
However, I do use heavy bullets, 150gr and heavier.  And yes, correct wiping procedure certainly is important.

Dellet, thanks for the offer will send a message to you.

Martin, I appreciate the feedback on your experience with the 30-20. I do not want to give up on this barrel yet, but was starting to second guess everything. Guessing this was build for a specific purpose by an old time gunsmith with knowledge we don't have readily available. 

Thanks everyone, 
Mike