does the latch work ? as they tend to stick and can be a pain to free up.
i have 3 x snider mk 3 and they are easy to work on.
when you get the breech off stick your finger in the chamber and check for rust as you tend to find it at the 12 oclock position......hard to remove lol...but possible.
it needs doing as you might not be able to chamber the brass.....and if you dont fully remove rust the first time you fire a strong load to fireform the brass it will stick in the chamber and you have to whack the breech to open...dont ask how i know.