1322 based stubby build (aka Noisy Cricket, Lol)

[ER00z]

Figured I should start documenting this one-off contraption... I'll add photos when possible.

Probably best not to replicate... I'm not an engineer. But I do have power tools and get bored on occasion.

I had this crazy idea to make a stubby 1322. The beginning of this idea can be found in this thread started by fellow member Splitbeing...
https://www.gatewaytoairguns.org/GTA/index.php?topic=216407.40

A mock up photo of what I'm thinking (same as in the thread above)
https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=216407.0;attach=469787;image

To sum it up, take a 1322, shorten the barrel, loose the on board pump, shorten the tube and then install a fill fitting directly to the valve so it can be pressurized from an external source (buddy bottle, pump, etc.).

Today I finished the barrel properly (squared off the muzzle, re-crowned, filed flat spot for sight). The length is 4 1/16", cut from a spare 1322 barrel I've had for 5+ years. Next is to tap the valve for an 8mm quick fill fitting. I'm thinking M8x1 threads are going to be the best bet given the (lack of) space available/material to work with. Plan is to hopefully go right down center of the nose cone and stop at approximately the same depth as the o ring groove, leaving enough material around where the valve is already tapped for the front trigger guard screw (which will be replaced with a hardened screw, 8-32 x .25" I believe). I'll check actual depth after drilling (before tapping) and make alterations if needed. Also, I won't be altering the valve internal where the check valve seats (if that makes sense). The fill nipples I found threaded for M8x1 also have an internal check valve, which I'll be removing, relying just on the valves-check valve. This way the nipple threads only see pressure while filling. Not planning on using crazy high pressures, although when it comes time for proofing... Well, I'll cross that bridge when it comes. I will say if everything goes as planned, the valve will only see "normal pumper pressures", I'm not trying to make a magnum with a 4" barrel. Single shot, top off with bottle when needed...       

I'll tell ya, it's a lot harder typing out stuff than visualizing it in your head. It'll be a bit before I can continue, at a standstill for a week and a half or so. This might make actual engineers/knowledgeable folks cringe a bit, if any major red flags are spotted, I'm always open to suggestions.   

[ER00z]

Looking over the 13XX's valve inlet half, I'm not thrilled with the amount of threading depth I'd have to work with, where the trigger guard screw threads into the valve really being the limiting factor. Also keep in mind, I have no plans to alter the valves internal dimensions, plan on keeping the factory check valve in place and not enlarging the inlet hole any deeper than necessary, aside from tapping the threads for fill probe (keeping it original diameter as it enters the internals).

I figure there are a few options...

1. Possibly mill the inlet cone down some and drill/thread straight down the center of the valve inlet to just past the trigger guard threads. Then install the fill fitting. Drill a dimple (or possibly tap) into fill fitting threads a little through the valves existing side trigger guard threaded hole, so when the hardened trigger guard screw is installed it also pins the fill fitting into place. (Hopefully ya'll understand that, Lol)

The problem I see with this is if pressure bypasses the threads of the fill fitting (during filling or the check valve fails) it'll possibly vent down the trigger guard front screw. Could use a bit of teflon tape to seal ...BUT if that screw lets loose... Only bad things can happen.

2. Use a 760 style valve inlet half. There's no drilled/tapped portion for trigger guard screw into the valve. Gives more room/material to work with while tapping the valve for fill fitting. Then after installing fill fitting, tap new threads for a shorter trigger guard screw. Probably wouldn't be a bad idea to pin the valve in a few extra spots also.

3. Original plan... Just use the 13XX valve inlet half and not to tap past the o ring groove. Drill the inlet hole then start the tapping process. Then re-measure the losses of the nose cone to rear of o ring groove. Finish with a bottom tap then install fill fitting.

4. Give up on trying to install a fill fitting on the nose of the valve... Just go through the side, Lol. It'll look a little odd but be much easier. This route will require a fill fitting with check valve.

The problem I have with options 2, 3 & 4 is the risk of blowing the fill fitting right off the valve. I'm not knowledgeable enough at the moment to calculate thread pull out force or the forces acting against the fitting. I'm working on that though, although I don't pick up stuff as quickly as I did a few decades ago (or better, Lol. Not old yet, just slowing down a little  )

From what I've found, very few folks have tapped directly into 13xx valves. Something like two or maybe three people have plumbed in pressure gauges, never a fill fitting that I'm aware of (at least posted in forums). Yes, that little voice in my head has been saying there's probably a good reason for that. As of right now all of this is theoretical, just ideas floating in my head. I would assume plumbing a fill fitting directly into a valve would be reasonably safe, especially if normal operating pressures are limited/regulated to 800psi or less... But you know what happens when you assume. If/when I follow through with this, the valve will be tested in a controlled setting, I'm thinking a sturdy covered submersion tank then pressurize to XXXXpsi (thinking ~1400psi  peak to test thread strength, this may change) then hold pressure/leak check with only the pressure left in the fill whip...     

[threesuns]

Following - Are you planning to attach a reg’d bottle via whip hose or just fill to 800-1000 psi and 1 shot and refill?

[ER00z]

Following - Are you planning to attach a reg’d bottle via whip hose or just fill to 800-1000 psi and 1 shot and refill?

Yes, to both... Depending on the configuration.

Original thinking was a small sized air pistol, one shot then top off. Played around with the idea of making it a two shot pistol, provided I could balance out the striker force, valve pressure and transfer port diameter for similar velocity shots. Also thought of using a regulated ninja bottle and convert to carbine. Lots of possibilities with these lego guns.
   

[ER00z]

Got thinking about the barrel band... I'd have to use a 13xx or 2289/760 type... or have one 3D printed for an external tube type... Well, decided just to use the factory one for now. Didn't want to drill it out to slip the longer barrel through yet (plus shave the bands front sight down), so spent some time reworking the barrel remains of what I previously cut... Ended up with a ~3.5" barrel... Completely ready to shoot (aside from no pressure in valve yet  ). Modified/shortened barrel band a little... hidden within tube, pressure fit for now.

Waiting for fill nipples to arrive, will most likely plumb one in from the side of tube into valve... Will see when the time comes.

So here's Noisy Cricket version 1.1

[ER00z]

Comparison to standard 13xx...

[threesuns]

Get a 60’s grip frame - just a bit slimmer/smaller - mite just compliment your crosinger (crosman/derringer)

[ER00z]

Get a 60’s grip frame - just a bit slimmer/smaller - mite just compliment your crosinger (crosman/derringer)

Nice!

Crosinger, I like that 

[ER00z]

So... If I learned something, the force pushing on that fill fitting can be calculated by taking the diameter in inches squared, times PI divided by 4, times pressure in psi... Equals force in pounds against fitting...

So 8mm is approx .315"... Plan on "800psi" 

Equation should look something like this when rounded off for ballpark estimation:

.315^2 x 3.14/4 x 800= 62.3 Lbs (-ish)

That's if I got those figures correct...

Still haven't figured out the thread sheer strength/pull out force calculations.