I put a +1 hinge pin in mine and a spring kit.
I load 115 grains of Blackhorn 209 a Win. 209 and a Shock Wave,250 grain or a Lehigh 250 grain and my groups run from 1/2 inch to 1.5 inches depending on how good I am shooting that day sometimes my cataracts bother me.

Old post but I noticed how a few were stating that MOA from a muzzle loader was an unreasonable expectation. I have a couple of sidelocks that, with the right load of course, will easily print MOA and even exceed it if I am having an exceptional day. My old man's Thompson Center Pro Hunter will print well under an inch with a few different bullets and loads. But, like lemoyne, he did a few modifications to his using that kit from Mike Bellm. It shot well before he did those but it is an exceptional shooter after the mods.