Re: Sears (Miroku) 45 cal muzzle loader?
I picked up one at a local gun shop about 20 years ago for $40.00. It was a poorly completed kit which I ended up rebuilding. The wood ramrod was of too small a diameter to be of much use for tight fitting loads, so I replaced the thimbles with 3/8" diameter and bored out the stock for the same so I could use a 3/8" ramrod. The trigger had been butchered, so that was replaced also, plus refinishing the stock and metal furniture. The stock was two piece with a brass spacer at the joint, so I removed that and sistered the two pieces together permanently with dowels. Mine will shoot .440 round balls, but they are an extremely tight fit, even with thin patches. .433 balls with a .015" thick patch load much easier and shoot well, so I tend to think of this rifle as a .44 caliber. Mine has a Spanish made lock, the same as on some of the CVA locks on muzzleloaders back then. The hammer needed a little tweaking to get it to line up with the nipple and hit square, and it also rubbed up against the lock sideplate, slowing up the speed of it's swing and giving inconsistent ignition. The nipple is a metric thread, 6-1mm.
Anyway, with that all fixed, it shoots very well. I only use real blackpowder, which ignites very easily with regular CCI #11 caps. If you use Pyrodex or one of the other substitutes, try the CCI #11 Magnum caps, which give a bit hotter flame. With 60 grains of Goex 3f powder and .433 ball/.015 patch, I took a Mule Deer buck at 90 yards with a through and through chest shot broadside. It was double lunged and ran about 75 yards before cratering.