The Craftmans Shop > Backyard Ballistics

Building a PCP airgun.

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cfellows:
Seamless stainless steel, 1.25" x .080" wall is rated at 9,000 PSI burst pressure.  That's probably 3 times what you'll be pumping your reservoir up to. 

I used 1" OD, .065" wall for my air gun.  It was designed for CO2, but I've pumped it up to 2,000 PSI with compressed air.  It rated at  9,750 PSI burst pressure.

Are you going to thread the ends of your reservoir tube or use socket head cap screws in a radial pattern to hold the end plugs in place?

Here's a picture of my reservoir, admittedly small for air, but fine for CO2...



I used 4 socket head cap screws in a radial pattern to hold each of the aluminum end plugs in.  The screw head is countersunk into the aluminum plug so the shear force is across the head.  Simple O-ring on each end plug keeps it sealed.

Chuck

Jonny:
I cant emphasise how dangerous this can be, your dealing with pressures in excess of oxy acetalene bottles and not tested!
Swat up on what you are doing, if its not you its others around.

Its not so much the rated tube, its the plugs in the ends which are the most vulnerable usually.
80 though wall i wouldnt want to put 200 bar in whether or not its passed a 300 bar test.
Mind one well known manufacturer uses 27.3mm bore with M 1.25 pitch :coffee: Blows at 245 bar thats about 60 thou wall!

30mm o/d with 2.5 thick wall hydraulic tube is pushing it for 350 bar with pinned ends. Yet going 20 thou thinner and 1/16" larger dia adds to weakness, dont assume for one minute that will hold 4500psi. These are nothing less than a potential bomb and have seen for decades what you boys do over there. Cap head screws should take the load on the head not the thread.
Cant quite see but think thats done right on the 1" o/d tube, heads going through the tube and in to the end plugs, the thread just stops them dropping out when no pressure in. Unlike a certain manufacturer your way and predecessor using mush head screws on top of o/d of tube with 3/16" screws having the shear on end plugs.

To pin the cylinder on 1 1/4" stainless G316S11 X 1/8" thick wall i used M5 cap heads 17 years ago. Took it up to 6300 psi before 1/8"BSP off the shelf thread sheared. Th end plugs moved as well stressing the materials also stainless steel.

I wont remind you of the numerous failings due to incompetant tatters, even if Ginb didnt make that cylinder, he messed with it and should have slung it back if he knew what he was doing! Carreers another totally dangerous as is any CO2 pressure vessel operating at more than rated value ie air at 200bar.

Jonny:
Neo think your missing the trigger mech.
If going underneath that will be very very deep.
Also not much point in the middle line of hole, the bottom can go there and trigger where the cylinder line is.

Or like number 21 i started and put on hold March 2003, missed the deadline and just sat round ever since.

Barrel and bolt top line. Knock open valve in middle like the predecessor to the Rapid and tube with trigger on lower line.

The ends will bellmouth after the thread on this tube at 4800 psi, done in 98.

All the parts are there in rough state inc the reg, it only needs the O rings and theoretically should work if it aint rotted away.

Jonny:
Number 2  Sept 93 old school style, 30 o/d x 3mm thick wall threaded 1 3/4" in to the tube with 26 TPI brass thread.
Note the long breach block for long scopes and ultra short hammer to loading from memory 2", most are over 5". Short hammer stroke 2.4mm not even to this day has anyone come close except the electric solenoids.

In use up to September 2005 three times per week rain sleet or shine, then finally decided to pack up 4 days before the worlds after 12 years.

Number 7 1996 rotting away using Tungum alloy tube 30 o/d x 2mm thick wall. Same burst pressure as 30x2.5 hydraulic steel. It works but never finished because it looks like brass and it isnt. Could have plated.


No miller at this point just a Myford ML7 toy lathe.

NeoTech:
I have been reading up on creating pressure vessels..  conclusion is that you shouldnt try to create anything beyond 200bar yourself. as stated by Johnny, the caps will become small projectiles if failing..   And i have gone way overboard on thickness of tubes. =)

About the trigger mechanis, yes they will be sitting underneth, but they will be kinda flat with a rotating sear, similar to a crossbows mechanics, with a small lever that keeps it from rotating. I have some drawings on a napkin i will post images when its cadded and simulated.  cause i'm building a bullpup design i'm not really that worried about the stacking height of the components..

And on other note, my project is a bit stalled.. cause i suck at machining and put a 12mm hole througy my block took three hours (100mm long, 12mm in dimater, on one of the edges of the block)..  and the whole setup almost killed me. ;)

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