8mm is 0.314961 inches. A .38 caliber measures .357, so your bullet is to small for a .38 or even .36 or .32. My SWAG would be it was probably intended for a .30 caliber firearm, something like a .30-30. .30-30's have been around for 100 years. That's just a guess though. If you take that info, and put about $4 with it, you can probably get a cup of coffee at Starbucks.