This catalog has some good images. Cut-aways of breach plugs and bolsters so you can see how they fit, and what the flash channel looks like. Good specs on the guns and rifles too.
Thanks. I used to have this catalog. I put together one of the first model Mount Rifle Kits (serial number less than 200) in the late 70's, and later bought the Mountain Pistol kit. Sold them both when I needed money to pay the rent.