A month or so ago I won a rolling block on GB. It was listed as 45-70? It turned out to be as close as I can determine to be chambered in 44-90 Remington Special 2 7/16.I trimmed some 45-2.6 brass to 2.44 and formed a sholder to head space and fire formed. Resulting in the pregnant guppy look. 
Next try was Buffalo Arms 44-90 Remington 2 7/16which came yesterday. The description lists it as .525 base but the headline lists .515. 
It's .515 which is the same as the 43 Spanish. The brass is formed from Star-Line 50-110. The BACO brass I'll trim and size to use in my Argentine RB. It has a thickness at the neck of .007. Already ordered Star-Line 50-110 brass from Midway and made a body sizer from all-thread for a .528 body. My chaŕmber expanded the 45 brass to .531and a fixture to hold the brass to thin the web .025.
Any way, the 44-90 Remington .515 base makes nice 43 Spanish with just a trim and a size and with Star-Line brass. 
WW