What model of the LeMat do you have?
Here's a little guide:
Spur trigger guard, spur hammer switch, lever barrel release: CAVALRY
Round trigger guard, lever hammer switch, knob barrel release: NAVY
Round trigger guard, spur hammer switch, knob barrel release: ARMY
I load the grapeshot barrel of my Navy model with 55-60 grains of Pyrodex RS or Goex 2F and a charge of about 1-1.5 ounces of OO Buckshot. The second barrel performs quite well in both mechanical and historical standards. For reliable ignition, I would not recommend CCI or Remmie caps, but instead, use the Vorderlader Zundhutchen No. 11 caps manufactured in Germany and sold at Dixie Gun Works for a very reasonable price. They are charged with a priming mix called Sintox, created in about 1880 and is more sensitive and reliable, escpecially for the second barrel in which the hammer throw is only about 1 inch, despite the heavy mainspring.
To keep the shot from rolling about loose from the concussions of firing the upper barrel, use a double packing of over-powder and overshot wad, preferable lubed in something like Vaseline or bore butter. Ram it fully to ensure no airspace exists between any buffer, propellant or shot.
The LeMats have a bowl-shaped breechplug at the end of the barrel, Dixie offers something called the breechplug brush for thorough cleaning, item number BH1023 on their catalog. Use the brush attachment with the ramrod of an in-line muzzleloader and you have the ultimate cleaning tool for that breechplug. For the barrel, Dixie also carry a 20 gauge shotgun bore cleaner.
PS, FLORIDABOY, if you are thinking of getting a LeMat, get the Navy model. It is more rugged due to the knob barrel release, different from the lever that would not flip down when the weapon fires. Go to the Dixie Gun Works website, find the LeMat Navy, and read the comments about it. My comments (name: Raymond Chen), Mec's and others are all on it. Just be sure though, nobody gave the weapon a rating lower than a 4-star. Many people are impressed. Accuracy wise: It is reasonably accurate for 25 yard to 50 yard shooting, and even though some people talk about not getting used to the grip angle, I found it very comfortable to hold and take aim, the sights are very good, and like I said earlier in this post, for the utmost reliable ignition, use the German percussion caps that Dixie sells.