He wrote about his first rifle a little in Pilgrim's journey - .50 cal, left-hand lock with a octogon to round barrel and made by Jud Brennan. I remember he said he used a basic 50 grain charge for squirrel all the way up and for "shooting at marks." I remember that because at the time, I had a .50 cal and that prompted me to load it down a bit and experiment with less powder.
This was the first volume. I never read the second, so I'm not sure if he wrote about selling that rifle at that point or if that was still before Mike Miller made his newer gun.