The round shown at the beginning of this thread is, indeed, a normal, brass-case cartridge “Ball M1911.”
Regarding US military experiments with aluminum cases of .45 M1911 caliber, I suggest the following reading:
“History of Modern U.S. Military Small Arms Ammunition, Volume I,” by Hackley, Woodin and Scranton, page 29 dealing with cartridges made prior to WWII.
“History of Modern U.S. Military Small Arms Ammunition, Volume III,” by Hackley, Woodin and Scranton, Page 22 dealing with cartridges made in the 1960s and early 1970s.
There is simply too much to put here.!
Below is a picture of Aluminum case .45 cartridges, which does not include those from Frankford Arsenal in 1931, 1933 and 1934.
All shown are from WCC or WRA and date from 1969 thru 1971. I show this only to indicate the large number of specimens there are. Those shown are all in my own collection, and do not by any means represent all known variations., unfortunately.
Edited to add below a picture of an Olin Corporation box label for Lot WCC-l-DAAG25-70 - C-0009 Aluminum Case .45 Ammunition: