The quest for true semi-auto.

I'm one step away and I'm stuck for ideas. The current (only partly tested) setup is reserve tank->regulator->solenoid valve->primary tank->solenoid valve, when the fore-end (priming handle) of the alpha trooper shell is cycled forward it hits a micro switch, which triggers the first solenoid to fill the primary tank. Sliding it back completes the chambering of the round, as it's a pretty basic 20mm conduit/petg breech, and the trigger fires the 2nd solenoid. Once fully assembled and tweaked it'll probably be an adjustable 20 rounds of slamfire BBUMB.

What I want is to go one step further and eliminate the need for the fore-end action, using some kind of electronic/mechanical/pneumatic gizmo to cycle the bolt for me. Being a bit of a novice to the wide world of gizmos i'm kinda stuck for ideas that would actually work, so if anyone else has worked on this please lemme know. One idea I did have is using one of those "generic semi auto blasters", but that would require replacing the pump handle with a backwards trigger which still leaves me with not-really-semi-auto. Another idea would be linking the air system to a stampede plunger, but I'm not aware of any successful breech designs.

So yeah. looking for any advice, or even external links to related works or even concepts.

Thanks guys.

Check this out, Semi Auto Longshot.

https://www.youtube.com/watch?v=cPNwjmPEHdc

Check out his previous update videos on it.

Update 1: https://www.youtube.com/watch?v=Ru4xSk-JWYo&feature=relmfu

Thanks Jason. Also found this. The blow-forward bolt is the biggest issue at the moment, I've pretty much got everything else sorted in my head, but simpler and less engineery.

http://www.instructables.com/id/Semi-Automatic-NERF-Longshot/step2/How-the-bolt-works/

I'm trying to get my head around how i could vent the bolt chamber to atmosphere after firing without having to learn to understand anything as complicated as microprocessors or 3-way solenoids. Push button almost semi auto would be easy enough though, just have like the rayven's accelerator trigger hooked up to a solenoid to vent after pulling the 'main' trigger to fire. This idea of needing a lathe is a bit bs i think too, could be done easily enough with an existing PT and some brass.

Also just found this. The gif halfway down the first post sums up what i'm trying to do. http://www.spudfiles.com/forums/6mm-semi-added-trigger-and-mag-t10075.html

I've always been meaning to try this out, for ages. Although, the compression spring will be the hardest part of it all.

Actually. That semi-auto longshot seems way too complicated. You should try the jacksmirkingrevenge gif image. It's so simple compared to all those 'solenoid' valves.

It still needs a release valve and an entry valve. I figured out i could put a micro switch in just the right spot so that it trips just after the bolt closes, opening the bolt to atmospheric pressure. Sounds tricky but I should be up to it (when I can be arsed lol)

From my understanding the spring just needs to match the firing pressure. So a 2 square inch bolt backplate firing at 20psi would need to be countered by a 2x20lb spring under compression. So I just find the most epic spring I can that won't break the bolt and dial up the regulator slowly. All it needs to do is allow pressure to build, then return the bolt when pressure is released.

"That semi-auto longshot seems way too complicated."

Yes. Partly because he's an engineery sort of guy that's proud of his work and wants to scare noobs so he explains everything in the most complicated way, and partly because he took a few longcuts. That said though I'm definitely going to be working more closely off the .gif when the time comes.

For anyone else thinking about this, the trickiest parts to machine are the bolt, plunger head and the 'plug' that blocks the bolt. They can all be made by adding delicious telescoping airtight ready made brass (for bolt and plug) to a standard plunger.