A leather Cartridge Shoulder Bag.
This well made bag was originally intended to take cartridges for shooting but of course, could be now used as a shoulder bag. The interior has a pocket to the front with a popper and 5 small pockets of various sizes behind it. The main compartment is plain. The adjustable leather shoulder strap is fitted to the bag on a large loop to either end to aid free movement.
Most cartridge bags are made of pigskin with a thick canvas shoulder strap so this one is a little different. This also suggests that it is mid 20th Century in date.