unknown post war? shell

[alwion]

this was from a Washington DC estate tag sale. I thought it was a variation of a baby whitworth, but the twist is the wrong direction. the measurements are very close to the projected measurements John use's in his book for a 1.9". it does have a very old tag attached, not able to read but some letters of writing using an old dip pen. many of the 1.9" whitworths went to South America, but the twist directions makes me think its something else. Post war experiment? looks pre cartridge era
weight: 2lbs 12.2 oz
length: 5.38"
flats: 1.837 ( one is slightly smaller)
ridges: 1.967
any ideas

[alwion]

sorry my photo skills are obviously wanting, I cropped these down alot from the originals, and still seem to enlarge oversize. my photo program didn't seem to have a size reduction like my old program

[emike123]

Saw that on eBay where it was called a Whitworth but I don't know about that.  It went for a fair bit.

I just got a new PC and rather than migrate my old photo editing software, I started using the free cloud program at https://pixlr.com

It has some kinks but is better than the others I tried, but they were by no means an exhaustive list.