I had my local gunsmith fix my laminate stock on my 375 Ruger Guide Gun. It was cracking out at the action tang area. About the same area as your muzzle loader. He is located on the east side in Tri-Cities area. Here is his contact information. He will guaranty his work and he is very reasonable on price. Turn around time is about a week.
Gerry's Gunsmith 1 (509) 627-0377 best time is early mornings and leave message with phone number.