Thanks jack, you've been a great help.

Is this a good piston?, a wooden cotton reel with bike inner tuber rubber for the sealing edge and a bolt down the middle with a washer etc, and I was also wondering what a good bumper would be.

Can I fill a piston valve with a bike pump (Max Psi 100) or wouldn't that close the piston? Would it be hard to make a piston valve that reseated or would it be too hard to do with just basic resources and budgets.

That a piston valve would be less efficient than a sprinkler valve when used with a blow-forward breech loading system. Also wouldn't it be a waste making a blow-forward if pistons can only be shot once (Correct me if I'm wrong) because you'd have to refill the air chamber anyway.

I'm deciding between the Blow-forward breech and making a piston valve, what do you reckon will have more power, and I was wondering if i could merge the 2 seeing as the breech seems to be just a loading system. Also can you make small piston valves such as a 15mm because PVC is super expensive over ...

I have so far built 2 air guns and both of them are pretty basic , the first one is just a fizzy drink bottle attached to a pvc pipe with a ball valve (could reach 130 Psi but wasn't very powerful) and the second was similar with a fizzy drink bottle as an air chamber but a water hose gun as a valve ...