There are essentially "two variations over time" as the Italians initially simplified the original Sharps gas check design by eliminating the gas seal plate and going with the floating chamber sleeve. Due to "quality control" randomness, the sleeve "floats" as intended on some, is loose and falls out on others, and is so tight it it does not move and cannot be removed for cleaning. (Some sleeves also will move, but cannot be removed.)
Possibly as a result of complaints, they reengineered their bogus design combining a removable gas plate and the floating gas sleeve.
So, one will run into the two variations on the "theme."
In gleichem Schritt und Tritt, Curt Schmidt
Not a real Civil War reenactor, I only portray one on boards and fora.
I do not portray a Civil War soldier, I merely interpret one.