Q:

.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.

Mods/Machinists

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Nice!

quote Cricket:

Cool, would love to see a video of you shooting one, I bet it is loud as fuck :4:

Yea really loud.. Id liken it to 410 shotgun or 9mm pistol sound.. not bad with the suppressor fitted though, more like a suppressed 9mm pistol.

This vid shooting grass carp really didint pick up the sound well but it shows the recoil on the .44 with a very mild tune of 190ftlbs..
Ill try get a vid of the .30cal with and without the suppressor some time soon

Wingman
I wished I had your skill, Your Machines, Your tools ,
Maybe its not to late,
Do you loan things out for free,
I could send it back to you in a few years as the skill level got better.
Mike

Cool, would love to see a video of you shooting one, I bet it is loud as fuck :4:

Yea crosman frames for now but I will build a better unit from scratch as time allows..
They need quite a few mods to beef them up for the heavy hammer spring etc
I got the ones on the .30 and .44 pretty good

Is the pistol grip from a crosman? Are those triggers worthy of such a gun, I have a backpacker with a shit trigger, you can cut the spring shorter but then it wont cock unless I pump it all the way up

quote Cricket:

Holy crap, Nice build. Will it get 1 shot per fill? 😉

Should get 3 or 4 even though I only ever need 1 :rofl:

A little more work on the breech tonight

Holy crap, Nice build. Will it get 1 shot per fill? 😉

I dont have the time at the moment to put together a full build thread for this little new one but will throw a few picks up as I go..

Finally spent a couple of hours on the mill and lathe and made a good start on a 9mm pistol.
I really like the way my little .30cal pistol handles but wanted a little more punch so have designed this one to shoot the .357 cal JSBs and a 125gr HP cast bullet.. It will be a little smaller than the .30 cal and will get a full length receiver/barrel shroud and open sights to give it more of an auto pistol look.

First pressure test

It was quite a challenge to drill the required four different sized internal bores with long series drill bits as none of my boring bars were just not long enough..
I will have to cut it in two parts to tread the barrel into the breech anyway but I will do as much of the machining I can while it is in one piece.

very impressive

thats some skill there mate

Thanks family Man for resurrecting this thread!! Would have never seen it otherwise!

Very nice work WingMan!
I wish I new how to plan out a project like that? Need some engineering skills…..

I’d buy 1…dirty hell of a good job!

Unfortunately out of my price range, nice gun non the less. Hope the other guys will have a blast with them.

This one is not for sale, it was a hand made prototype, more of a proof of concept.
I am considering having a bunch of parts cnc made and putting together batch of pistols though, Id probably make them all 9mm to shoot light weight (125gr) cast bullets and the JSB 35cal pellets.. they wont have the Crosman trigger/grip though, it will have a full custom trigger/frame and the barrel will be fully enclosed. Depending on CNC costs Id guess they would end up about $950-$1000 a piece.




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