.30cal big bore pistol build

This build started as I had a short off cut of air vessel tubing from a length used on a rifle build..
However it is VERY short on big bore standards as they require a large section of tube in the rear to accommodate a large valve, hammer stroke and hammer spring, in this case if I was to build the same action as the .30 cal bullpup it would account for 3/4 of the length of the tubing which would be kind of pointless as there would be no volume left for air.

My goal is to keep this pistols OAL to 300mm which means no just adding a larger rear cylinder end cap to extend the hammer springs working stroke rearward which would have been easy.
This is where my challenge started and I am building a bit of a prototype to test a few new dimensions and components.
The first thing I wanted to achieve was the longest barrel and the shortest receiver length I could possibly get away with which meant shifting the valve body as far rearward as I could without loosing so much
hammer travel that power would suffer.

I have used a different hammer spring which is shorter and larger in diameter than the one I used in the .30 Pup which gave me 12mm less length on the springs total bind length when cocked.
Also being a short barrelled pistol a lighter hammer can be used to shorten dwell time on larger valve ports to get similar velocities form a larger but shorter burst of air, this gained me another 6mm.

The last and most drastic design change was the valve body its self, it is 8mm shorter rear of the transfer port than the rifle length valve and I have manage to claim back another 13mm by recessing the valve return spring into the rear of the valve.

Another change Ive made is reduced the poppet valve shank from 1/4″ to 5/32″ and made a stepped collar with a retaining grub screw that locks down on a filed flat..

A recessed valve spring seat means a flat or slightly recessed faced hammer can be used meaning more weight and a shorter hammer.

The new valve is much shorter in total length and still has loads of meat for countersunk retaining cap screws and still within the minimum safety measurement to the edge of the material. The smaller 5/32″ valve shank means I can use off the shelf M6 X 6mm cap screws to retain the valve in the cylinder and they still wont breech the bearing surface of the valve shanks bore like it did in the rifle valve with the 1/4″ shank which required the cap screws to be cut very short.
The over all valve travel remains the same as the rifle sized valve.

The valve spring I have used a stiff little bugger too which should help with efficiency not that that will matter much with this little pistola as it will have a low shot count with maximum power tune.
The best part is the new dimensions make the back end super short which will give me a 7″ barrel and a 130mm receiver compared to the 150mm of the pups, which will be low profile and made from a smaller material than the pups, the greatest advantage is I now only have a 140mm section of tubing behind the air reservoir for the firing mechanism compared to the 200mm of the rifles design but will have the same air delivery only with the dwell tuned to a pistol length barrel.

If all goes to plan this will lead to future pistol builds being shorter lighter and have more air capacity for a higher shot count.
I will be using a rotary multiple barrel transfer port design in this pistol which uses 3 smaller rotary ports within a cut groove rather than one large transfer port cut into the lower section of the barrel. This will allow me to use smaller cast bullets, round ball and JSB pellets without the problem of them dropping into the transfer port and jamming things up. more on that later.