John, it's a single shot, total tank dump.
Stan, The trigger is a simple air bleed valve that vents the diaphram chamber and allows the valve to open, the same as when the irrigation valve solenoid lifts and vents. The bore is smooth. I'm retiring from my short career as a gunmaker. The hours are long and the money is short. Now seeking a new career that has less hours, more money and more libations.
RWTF, No stainless was harmed in the construction, except possibly the female flare nut and sleeve. The tank was a blue propane torch tank that I removed the base from and soldered in some 1/8" NPT brass bungs and drilled out the neck, the tank fitting is a modified pipe fitting in which I modified by single point threading the 1"-20 thread internally to fit the tank, The Irritrol valve is plastic, the trigger guard is cold rolled mild steel, The AR-15 grip fitting is aluminum machined from a block, the tube assembly is steel, the back of the barrel has an aluminum fitting machined to fit a -12 flare and thread into the bore of the barrel with 32 threads per inch, the barrel is 2" x .065" aluminum, the barrel shroud is 2.5" x .065 aluminum tube, the aluminum picatinny rail is contour machined to fit the shroud, and the barrel to tank clamp is machined from 1/2" aluminum plate.
It took a couple hundred dollars in materials, not counting any scrap and ideas that didn't work. Labor and span time was probably 6 weeks at about 25 hours a week on average. Design work was on the fly mostly and the rest spent over a good cab or beer.
The wife of the recipient originally wanted to do some work to it to put some of her labor into this gift for her husband and thought she'd paint it FDE (dirt color), but after seeing it cleaned up and nearly finished, she thought it should show the metal work. So, she's asking me for counsel here. I'd have all the aluminum anodized in playful toy like colors, but she's still on "tacti-cool" looks. Maybe we'll leave it bare except for painting the steel parts.
Anyway, it was a fun project. But I'm happy to be finished.