It is a bullet I believe. 12 grams puts it at just over 185 grains. A good bullet designed to take big game animals will retain the vast majority of it’s weight, 90% or more. So I would assume it was probably a 200 grain bullet which is fairly common in the larger, magnum type rifles of the later half of the 20th century, and still sold today. Without knowing the diameter of your bullet, I’m going to guess it’s from a .300 Win Mag, 7mm, or .30-06. It has the classic mushroom shape of a bullet that made impact with something soft such as a deer or moose. If it had hit rocks or trees, or dirt it probably wouldn’t be so perfectly mushroomed out like that. A large bullet such as that can easily pass completely through a deer and come out the other side, in which case the hunter would have never found it, or even try to. It’s a pretty common find actually, but cool none the less. I still save every bullet I find, the more common and modern ones go in a glass jar, and are still cool to look at. If your object is made of lead, or shows signs of a copper jacket, it is almost certainly a bullet.