"Outer Diam" is the inner diameter of your chamber tube.

"Inner Diam" is the outer diameter of your barrel for a coaxial cannon.

If your design is not a coaxial, the "Inner Diam" should be zero.

That would be pretty sweet. Keep us updated.

Just as a matter of opinion: cam locks all day every day. In a mounted configuration like yours screw breech works well enough, but any usage where the barrel is free to move in any other axis than forward/backwards (and rotating) they become very annoying.

It might be worth giving this a read, or at least a quick skim: FM 3-22.90.
Not too familiar with mortars myself, as the only time I got to watch a team they fired a total of two flares.

You could also spring-load them or even just add a larger handle to the valve as well. I think with a few bucks worth of tubing/fittings, and a small 1/4" ball valve, you could really make those three sprinkler valves work a lot better as well though, all depends on what you want to do.

I have all there plans from many years ago before they sold the site i will look for them and post them if that's allowed since there out of business

i have found the plans and will upload them shortly I have been busy trying not to lose everything but I wanted to post an update so your not left hanging ill probably take pics of them and upload them that way it will be the easy way t save etc. I also have a few others I may upload like the PAC 6 ...