The rounded rim remind me of a 303 british but its not even close in diameter. I was looking for a 11 mm rimmed straight cartridge but I'm stumped.
Might be a 44-70 Maynard.
Here's a picture of a 44 70 maynard round that recently sold
https://www.proxibid.com/Firearms-Mi...ation/43889035
Maybe you can find something here
http://www.cartridge-corner.com/riflelist2.htm
Boolit appears too small for the maynard.
.44 Evans Long New Model
this one is close but not close enough.
Dutch
11 mm Gasser/ Montenegrino ?
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 |