If it is, it was made in a really bad mold, that seam line around it and the HUGE sprue would make it pretty much useless as a bullet unless it was trimmed really well. I'd be inclined to think it's a home made split shot fishing sinker that for whatever reason never got split. If you can get ahold of a digital caliper and post a measurement in 100ths of an inch that will tell us if it's the right size to have been a projectile.