.357-.358 is the exact size for the .38 caliber colt revolver bullet. This cartridge was originally developed in 1875 and adopted by the U S Army in 1892, but the diameter of those was .361, which rules out yours for being that early. Colt came out with the smaller .357 bullet with the idea of adapting the .36 caliber muzzle loading revolver over to metallic cartridges, in 1874, so it was the parent of the colt long, which lost favor in the war in the Philippines, 1899-1902, when the army decided they needed a larger pistol cartridge and adopted the 1911 .45 ACP. In the mix of all the .38 pistols and cartridges from that time until now, the .357 bullet has remained constant. Even though the model 1911 was the service pistol for years, the military used .38 caliber revolvers for various purposes at the same time, and the bullet you found has been real common, especially with the police. I know a pilot that flew Corsair's off the USS Princeton during the Korean war, and they all carried .38 specials. I've hand loaded many .38 cartridges, and I'm not familiar with the hollow base, which makes me think your bullet is an early one, but I have no proof. After all I've said, .38's are still used today, as are .357 magnums, which are the same size bullet. All of this is from an old man's memory, perhaps someone with younger brain cells will have something to say, and we will find out more. One fact is true, you have a .38 bullet.
