Glad I kept mine !!!! I did so to preserve the technology and perhaps one day see the carbine improved and back in production. Granted, plastic parts suck !!! Early Volunteer carbines did have sand cast aluminum lowers that used greasegun .45 ACP mags. There were also 9x19mm versions using Sten mags. The later plastic lower carbines used Thompson mags and worked well. No drums were ever employed AFAIK. Though some custom adaptions have been made both functional and decorator. These Volunteer carbines used square tube receivers.
Previous Thompson clones such as the Spitfire carbines were open bolt, round tube semi-autos later banned by the Feds. Eagle carbines I believe were grand-fathered as OB semi-auto items. I should check my notes. There is a Spitfire NFA collector-shooter website.
The Manchester Volunteer carbines (and pistols) production ended when Mr Manchester passed away. Revived popularity and current scarcity has driven prices of these "econo-arms" out of sight.
VD in AZ