I don’t have any pictures, but I punched spots for the second set of radial holes in the pipe using the same template as last time. I then drilled one of them.

The next thing I did was carefully push the divider and block assembly into the pipe. It had to be a really straight shot, since the holes needed to overlap. It took a couple tries, but eventually it got it so that I could see a little sliver of the divider hole through the hole in the pipe. From there I carefully worked an awl into gap an brought the holes into alignment.

Now that the divider was held in a known position, I was able to drill the radial holes through the pipe and into the divider. As with the end cap, by drilling the holes at the same time, I got around any alignment issues.

I couldn't help taking the divider back out to see how the holes came out. The alignment came out great!

Now that it's out I figured I might as well tap the holes. I also drilled the holes in the pipe slightly bigger so the screws would fit (my first holes were the tap size).

After that I just put everything back together and put in all the radial cap screws. I don't have a picture unfortunately. With this part done, I pressure tested the chamber, it holds AIR! That's a relief!

I the course of the pressure testing, I figured out that you can't pressurize a quick exhaust valve from the cylinder side. Basically, I'd been planning on filling the cannon by pumping air directly into the space behind the piston, but that's not possible with a qev. If you do the air just leaks out immediately.

I was eventually able to get it to seal by holding my thumb over the exhaust port, thus giving air some time to leak around the diaphragm into the “in” side. I was then able to slowly add air to the cylinder without it opening. Obviously that’s not a permanent solution.

I bought some new fittings from McMaster so I can put the fill valve on the in side. So that solves that problem.

Next issue: I've got to install a one way valve that allows air to pass from behind the piston to the air chamber proper. With my PCV cannons, the leakage around the piston seal was sufficient, but based on the other o-ring seals that's not going to work on this one.

I thought about how to do this for a while. I could add a one way valve externally using banjo fittings But I’m worried that a tapped hole in the pipe wall might be leaky. Luckily I think I’ll be able to fit a valve directly into piston back since it's 3/8in thick.

These looked like exactly what I want, but the quote came back at $40 each. I could swing that, but eh.. Feels like a ripoff for something that could be as simple as a ball and spring.

Enter the ball and spring!

I think building it will actually be pretty easy. I added a little spring (#9435K35), a delrin ball (#9614K22), and some #4 screws (#92949A105) to my order. Done.