Looks like some kind of swager.
That rusty hulk is a Model 28 Improved, Belding & Mull reloading tool.
It should clean up easily. Finding a complete die set is another matter. I had to buy three of them to get a complete die set.
The 28 Improved was the final design of this tool and it stayed in production till 1965. They sell decently on eBay, they are not extremely rare.
BP | Bronze Point | IMR | Improved Military Rifle | PTD | Pointed |
BR | Bench Rest | M | Magnum | RN | Round Nose |
BT | Boat Tail | PL | Power-Lokt | SP | Soft Point |
C | Compressed Charge | PR | Primer | SPCL | Soft Point "Core-Lokt" |
HP | Hollow Point | PSPCL | Pointed Soft Point "Core Lokt" | C.O.L. | Cartridge Overall Length |
PSP | Pointed Soft Point | Spz | Spitzer Point | SBT | Spitzer Boat Tail |
LRN | Lead Round Nose | LWC | Lead Wad Cutter | LSWC | Lead Semi Wad Cutter |
GC | Gas Check |