You have a contradiction here. Mauser is German, Not British. In 1916, the two were at war. What your rifle is worth will depend on what you have, the condition, and originality. Without a detailed description, can only guess somewhere between $50 and $500. Sorry-
priceless
rsi would say the value of the spanish mauser and bayonet value at 695.99 dollars
value depends on overall condition
765.00
Requires professional appraisal
The link at the bottom of this page will take you to a good site on military surplus firearms, including assembly and disassembly of the Mauser rifle. Your bolt MAY need to be cocked.
The "British"- meaning the British government- did not make an 8mm Mauser rifle. Some private gun makers in England have- but without more information, there is no way to answer. Please repost your question with some identifying information, and we can try to help. Let's start with all markings on your rifle.
50-250
100-400 USD or so
50-200 or so
The Royal Mint produced no Crown (Five Shilling) coins from 1903 to 1926 inclusive.
IF the bolt is properly installed, are you trying to close the bolt on a cartridge? The Mauser is designed to feed from the magazine- if you single load a cartridge, the extractor may not fit over the rim.