The rimfire cartridge was introduced the same year, and the hammer looks like it was designed for striking a rim. Also, the caps (or cap mounts) are usually more obvious, and I don't see them here.
The article suggests that this was the only one made, and that it never went into production. And I an probably misinterpreting it, but the article includes text that suggests that the individual cylinders could be swapped out, which is intriguing. With a 2-man team, you could just keep firing this continually as someone else swapped out fired cylinders as they went around. Utterly absurd... except as an emplaced rifle it'd be slightly less silly, especially if the cylinders were swappable.
Anyway, probably rimfire? The timing works, barely.
There's a third level not shown here. A compound magazine of compound magazines. You wear it like a hula hoop, although it is not recommended that you try to use it like one
That's only for carrying, not use, of the hula hoop compound magazine. Instead, has a diameter of 4 ft. It is expected to stand up like a wheel touched the ground at the bottom of the compound magazine being mated to the gun. To change magazines, you shift your foot position slightly allowing the "wheel to turn" as the next magazine slides into place. The downside is that you are now facing about 15 degrees left or right of your target. The ideal use case is to be totally surrounded, and also not worry about killing your allies with friendly fire. /s