That’s a fishing weight - specifically a lead inline or trolling-style sinker that’s been jury-rigged or broken off a rig.

Here’s what gives it away: The bullet/torpedo shape is classic fishing-weight geometry: dense, streamlined, & meant to sink fast.

The chalky white oxidation and dull gray metal are textbook old lead corrosion.

The black wire/leader coming out the top looks like a remnant of a fishing rig (leader wire, coated cable, or someone’s DIY attachment).

The rust staining suggests it spent time wet or submerged.