Tough call IMO , something 'Blew' or poked through that lead.
Looks like a large cal.lead slug fired n mushroomed then hit by a smaller jacketed bullet.
I’m sure there are others here who will correct me when I go astray, but a couple observations. Most of the cw blow throughs I’ve seen aren’t as mangled as this piece of lead. Assuming that the act of blowing through released a great deal of pressure from behind the bullet, and therefore the velocity to cause such deformation. Second, I have dug several things that looked similar to this that were modern shotgun slugs….for reference a 12 ga slug is a touch over .70 caliber. A 1oz slug is fairly common for a 12 ga, and that translates to ~438 grains. I think we’ll all agree that based on the condition of this piece a ~5% loss of original mass is fair. The removal of patina removes any guesses I have of age…..so I’m guessing a modern 12 ga slug.
Probably exactly what it is Brenneke slugs from Germany have a base that continues forward through the slug expanding it. Only problem is it punches through from the rear the slug in the pic has been punched from the front.ive recovered a good many slugs from bullet traps n back stops where a smaller caliber round punched through a expanded slug when you fire thousands of rounds between clean up its just gunna happen not saying that that's exactly what happened just I've seen many and you can't tell the difference.
I’ve dug fosters (I assume they are fosters) that look very similar and both in the pics “almost” blew through from the front.
This is what I cast and use now the mold comes from Slovenia and is the best quality bar none where a foster bananna peels this baby just keeps on chooglin
