Simplest Self Loading Semi Auto

[Brian the brain]

Have a look here: http://www.spudfiles.com/forums/viewtop ... tml#188632

This, combined with a blow forward bolt will give you powerfull repeating shots.

If you want true semi, you will need a 3 way valve to either fill, or exhaust.

@Jack: I'm a bit surprised you called my snapvalve QEV system complicated.
It's not.
It does however waste more air than the method you suggest in your diagram, wich does not use pilot volume.

In essence your diagram suggest a snapvalve, wich doubles as a bolt.
So it too will have the problem of not sealing in full auto mode.The poppet will always open before the bolt reseats.
Your idea is therefor more complicated

If one would combine both the poppet and a blowgun, but " forget" to seal the poppet properly,( leave out the rubber washer or O-ring) in other words make it leak just a tiny amount, you will have a true semi valve, in a sence,like the one in a pneumatic nailgun.

keep pressing the trigger and you only get a tiny hiss.Release and the bolt will reset fully.
Make sure to exaggerate the bolt diameter compared to the covered hole to get maximum boom.
I reduced the diameter of the hole the piston sits on from 8 to 6 mm and it is now almost deafening.The smaller exposed area means almost twice the pressure is needed to open it, yet the " snap" area remains the same.
Under this higher pressure it will snap open much, much faster.

In other words, I could now make my bbmg into a mmg

[jackssmirkingrevenge]

I'm a bit surprised you called my snapvalve QEV system complicated.

It depends, if you buy a QEV and a pop-off valve, it's easy, but I tend to look at things in terms of fabricating them myself. This design for example used only basic materials and was quite a chore to make.

In essence your diagram suggest a snapvalve, wich doubles as a bolts, so it too will have the problem of not sealing in full auto mode.The poppet will always open before the bolt reseats.
Your idea is therefore more complicated.

I had fallen into this trap when I made a prototype, however since the OP was asking for a semi-auto mechanism, this design is perfectly workable.