That is a lovely example! I have quite a few of these and most if not all of the 1915 dated ones saw service and show it, often then being traded to the Britishicon and reissued to Royal Marines. This one looks like it was spirited away, or was given to someone and never saw much service. It has no unit issue marks which is a clue as well. The pins were put in the bolts if memory serves me over in Britain about 1916 or 1917 to prevent incorrect reassembly, so this one was not present for that. That said, it has the LC stamp which is for Large Chamber--a slight polishing to allow better chambering of crappy British ammunition. Whatever its history it is a lovely piece and in excellent condition. Your son has excellent taste--that is a great piece of history and a fine specimen, and I hope it remains in your family to be appreciated for the next several decades!