Letter opener

Poorly made letter opener made from the driving band from a WW1 artillery
shell. Bullet is marked on the base - ARS D 4:07 and is .315 in. dia. Can it be dated?


I think the bullet is an 8mm French Lebel made by Atelier de Constuction de Rennes, Rennes, France

The answer is in the question. “4.07” = 4th Quarter of 1907.