Your bullet has "reeded grooves," and the earliest these were manufactured was just before 1900, 1890's + or - a couple of years. The reeded groove was usually used on pistol bullets, at least early on. We need exact measurements to tell you the caliber of your bullet, but I'd venture to guess that it's NOT a 45-70 rifle bullet.
This is a picture of a 405 grain and 500 grain 45-70 bullet.
Your bullet has been fired and damaged, but it could have started out looking like this .45 caliber Colt revolver bullet.
Looks like some of the bullet isn't even with the zero on the left. If that's the case it still might be .45 caliber, which is only 7/100 of and inch larger than .38.