Rings made from spent bullet casings by Brendon Jaine in his backyard workshop in Invercargill, New Zealand. 

Material: Brass, spent 308 bullet casing

Ring size Aus/NZ: O - Q Adjustable

Interior Diameter: ~19mm

Would fit: smaller man's finger or average woman's finger

Measurements are approximate because these rings are not perfectly round, so sizes are guesstimates/averages. The bullet rings are all easily adjustable. 

They have some pitting and dints from their previous use, and all are slightly different from each other, and may have slight differences from these in the photos.