
It's meant to shoot water. One submerges the muzzle (the tiny hole in the front, shown below.)

Then pulls back the handle.

The seal is perfect, and it holds 175ml's (about 6 ounces).
So I glued a 1/2" PVC coupler to the front...

and after trying different barrels, settled on a cpvc barrel.

It's entirely manual powered, and due to the seal, the device cannot be primed if it's loaded (a simple matter to slide back the handle before a dart is loaded.)
Just aim, and shove the handle. I'm only getting about 35feet flat, using tag darts. (I'm not exceptionally strong). I suspect a stefan and PETG barrel combination will get better ranges, but I think the biggest improvement is going to come from slapping a spring inside. (I have not yet opened up the device, it is glued at every joint and does not have screws, near as I can discern.)
It strikes me as an amusing alternative to other simple blasters, and has some potential. With the foam layer removed it has a rather slim profile, which may make it quite fitting for integrations into a primary wth the addition of a notch or other catch mechanism, and a simple trigger.

If anyone else goes in search of one, they were with the pool toys (which at the location near me was separate from water guns, for what that's worth.)