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**Mike Irwin** · January 29, 2018, 10:20 AM

U, as .44 AMP notes, was a headstamp used by either Union Metallic Cartridge company or Remington-UMC.

A single U with nothing else on the headstamp was used ONLY on rimfire ammunition.

"neck case"

Assuming that means a bottle necked case, which eliminates .30 caliber rounds. I know of no .30 caliber bottlenecked rounds that were rimfire from that era.

"I would guess it be at least 30 ga."

30 gauge, as others note, is approximately .52 caliber. That and the length of the round narrows it down, but it's still difficult as we're having to make a lot of assumptions.

"There were early cases that used an inside primer, but they were centerfire. Those cases LOOK like rimfires, (unfired) because there is no primer visible in the center of the case."

The only issue with that is that internally primed centerfire cases did not have centered headstamps -- it could interfere with the priming. Late internally primed military cartridges had headstamps, but only around the rim, nothing in the center.

My best guess, based on the very limited information we have? I think chances are good that it's a .56-50 Spencer cartridge.

January 29, 2018, 10:20 AM	#10
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,379	U, as .44 AMP notes, was a headstamp used by either Union Metallic Cartridge company or Remington-UMC. A single U with nothing else on the headstamp was used ONLY on rimfire ammunition. "neck case" Assuming that means a bottle necked case, which eliminates .30 caliber rounds. I know of no .30 caliber bottlenecked rounds that were rimfire from that era. "I would guess it be at least 30 ga." 30 gauge, as others note, is approximately .52 caliber. That and the length of the round narrows it down, but it's still difficult as we're having to make a lot of assumptions. "There were early cases that used an inside primer, but they were centerfire. Those cases LOOK like rimfires, (unfired) because there is no primer visible in the center of the case." The only issue with that is that internally primed centerfire cases did not have centered headstamps -- it could interfere with the priming. Late internally primed military cartridges had headstamps, but only around the rim, nothing in the center. My best guess, based on the very limited information we have? I think chances are good that it's a .56-50 Spencer cartridge. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.