This site's Steve Z. builds large bore ML's of up to 2 bore. He had a bunch of guns for sale right now. Should be listed or available on this ML forum.
I routinely shoot my .69 English gun and my buddy has a .75, also made by my bro. That is a big bore in my opinion, as in 11 gauge.
Shooting 600gr. of round ball with up to 200gr. of 2F is plenty & is quite accurate & about all the recoil this lad will put up with.