A blowback pistol with revolver type frame and tube magazine was built many years ago. Not a sucessful design so only few exist.
Instead of a regular cylinder this pistol used a two chamber flat slab that rotated 180 degrees at each firing.
The tube magazine was curved and fitted inside the revolver type grip.
When fired a breechblock in the upper rear of the frame blew back and the fired cartridge case was ejected, the chambers then switched position. The lower chamber being empty a cartridge was fed into it automatically , when the upper chamber was fired the process repeated till the magazine was empty.
Not sure but I think this system was later adapted to a light automatic cannon.