18gr is a VERY low load with any .44cal revolving pistol. The recommended load for a .44 cap and ball revolver by DGW and muzzleloading forum is something around 25 - 30gr of 3Fg or the sub equivalent, but don't let the opinion of about five million other shooters influence you in any way....
Mosts folks use either a Wonder Wad or grease cookie OR grease over the end of the chamber. Dunno anybody who uses two out of the three. But then, if you are only using 18gr, you'll need something to fill up the yawning chasm in there..
tac
www.muzzleloadingforum.com