Welcome to the board! You’ll find a lot of expertise here, but I’m not one of them. The gun appears to be crudely mad, not at all typical even the plainest English work. I’m betting it is Belgium made and was either sent to England for proof or has fake Birmingham proofs. W.W. Greener, writing in the late 1800’s, complained that a lot of Belgium work intended for sale in North America had fake proofs. Just guessing.....

When an old man dies a library burns to the ground. (Old African proverb)