Try here:
http://www.enfieldrifles.ca/main.htm
for a catalog of the stamps & other marks. Enfields are famous (infamous?
) for arcane stamps & hieroglyphs.
The proof (
BNP,
not BMP) should be 18.5 tonnes as has been said. The BNP stands for Birmingham Nitro Proof (from the Birmingham Proof House, London Proof House was just "NP") & was stamped when military rifles were released for civilian sale. The 18.5 tonnes was a system of pressure measurement in use at the time & doesn't mean it can take an 18,5 ton weight or anything, its just nomenclature that was in use.
There are makers marks, proof marks, ownership marks, inspector's stamps & so on so it takes a while to figure them all out & some you probably never will find as they were just "Inspector 12's" mark he checked something.
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Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”