Shortly after the last post I realized that the threaded end was a bit of a waste (unless you're using copper fittings anyway...and even then it's not necessary. Aaaaaaaaaaaanyway, this launcher head is functional so I'm going ahead with it. I added a coupler as a physical stop so the bottle won't slide down too far. Makes it a lot easier to use (and makes it look a little more like a spark-plug).

Hopefully later this week I can pick up the parts and make one of the simplified launchers and (more importantly) take pictures as I go, so I can also make a guide for others.

Side note: It's very frustrating to realize that 90% of my work is just complete bullshit. Every (relatively) straight cut of PVC takes me several minutes to score, trim, etc. Even then it's usually not completely square...and almost every time I do a different aspect of a project I have to put something else back up, I have so little space, so little money. This sort of thing is why I've cut back on doing projects. Although enjoyable, every project is a constant reminder of how little money and space I have to do...anything

Update:
I've put the launcher head together. An important point is that the bottom pipe on the launch head is sealed/reinforced by a section of capped copper tubing. That means the launcher frame doesn't have to hold any pressure.