.360 bore
The .360 bore is one of the smallest shotgun bores. Its main uses included collecting ornithological specimens, pest control, and self-defense, often concealed in walking stick or cane guns. The .360 bore was first created by Eley Brothers Ltd, a London based ammunition company founded in 1828. The .360 bore never gained widespread popularity,  because it offered little improvement over the smaller 9mm (No. 3 Bore) rimfire or the larger .410 bore. Therefore, making it hard to come by in the present-day. The .360 cartridge was one of the smallest of the shotgun bores, but never achieved widespread popularity. Its main uses were for collecting ornithological specimens and destruction of small vermin. It possessed no real advantage over the much more popular, cheaper 9 mm (No. 3 Bore) rimfire garden gun. A .360 bore load is often defined as a "2" orange-red paper cartridge with a brass head and rolled turnover. White top wad. Loaded with No. 5 shot." References

 https://www.iwm.org.uk/collections/item/object/30027828

Shotgun shells