SpudFiles

Hey airheads, following on from the failure/stupidity of my last attempt to make a high pressure .50 calibre piston coaxial i decided to up the anti so to speak and instead of using PVC as the chamber i used Aluminium.
The chamber has an i.d. of 33.7mm (spare piece left over from my combustion barrel).
It's features include- Alloy chamber and barrel, Acetal piston (o'ring and integral Polyurethane sealing face) length 33mm, weight 15grms.
Barrel length of 850mm.
Easy fill by schrader valve that is tapped into the endcap.
A pilot volume of 3ml's.
Piston travel of 3mm.
Chamber capacity of 60ml (hence the name Double Shot) or approx 2.5ci.
The ability to hold INSANE PRESSURE.
Last but not least the chamber is GOLD PLATED, if not a bit motley.

I have only tested it to approx 80psi, at witch my tight fitting ammo has trouble leaving the barrel
I hope that the increase of pressure to 350-400psi will have the desired effect of propelling the ammo to around 700fps.
If anyone can see a problem or has any ideas for improvement please talk up. I already plan a bigger chamber to around twice or three times the size but i'm not sure if my arms will fall off whilst pumping up the sucker, or if will have an appriceable effect on velocity.





How smooth is the chamber!!!

WOW, I want one :p
your right that chamber does look very smooth

effin' WOW, that was worth the wait! This is what my minis would look like if I had a lathe! Definitely get a shock pump and take it up to pressure

I have only tested it to approx 80psi, at witch my tight fitting ammo has trouble leaving the barrel

This worries me, are you sure that enough air is flowing from the pilot chamber to the main chamber? Maybe you should make sume notches in the front of the piston as suggested below:

jackssmirkingrevenge wrote:effin' WOW, that was worth the wait! This is what my minis would look like if I had a lathe! Definitely get a shock pump and take it up to pressure

I have only tested it to approx 80psi, at witch my tight fitting ammo has trouble leaving the barrel

This worries me, are you sure that enough air is flowing from the pilot chamber to the main chamber? Maybe you should make sume notches in the front of the piston as suggested below:

Thankyou JSR, i had the same worry. Suggested alterations will be carried out tomorrow, i'll use a 6mm ball nose cutter, is that large enough if i make two grooves do you think?

Holy F*ck! man that is nice! I am mesmorized by the shininess of it.

why not drill two small holes instead of cutting out part of the oring? just a suggestions. what are you using for your barrel?

As always, perfect clean construction

I really like it, looks like it can do some nice damage

Last but not least the chamber is GOLD PLATED

Bling a ling!!!!! Thats a real pimps "piece" now you can roll in style...GOLD plated style hella yes! Your cannons kick ass! Nice build mate.

experament-u2 wrote:why not drill two small holes instead of cutting out part of the oring? just a suggestions. what are you using for your barrel?

If you drill two small holes, that will let the air back through the piston when you activate the pilot. By cutting groves in the front as I suggested, you have effectively created a check valve that allows air forward while filling, but seals when you activate the pilot.

i'll use a 6mm ball nose cutter, is that large enough if i make two grooves do you think?

That should suffice, you can use this pump piston head as a reference.

Man that is a nicely built "mini"??? I like the way you cut your own threads, i don't have that down yet, but i'm working on it. What kinda lathe do you have? CNC, manaul??? I have a HF 8X12 it's manaul and lacks the quick change gear box.

jrrdw wrote:Man that is a nicely built "mini"??? I like the way you cut your own threads, i don't have that down yet, but i'm working on it. What kinda lathe do you have? CNC, manaul??? I have a HF 8X12 it's manaul and lacks the quick change gear box.

Thanks for all the comments, The lathe i use is a big chinese made thing, 660mm swing with a 2000mm bed. I gain my info in regards to threads in machinists info books, but most of my threads are not standard.

Gear box is the only way i can cut a thread

this may sound like a stupid question but how do u pilot it?

to_live wrote:this may sound like a stupid question but how do u pilot it?

I pilot *it* by depressing a small "pin" inside the valve. Think- if you were to deflate a car tyre, you would press this pin or unscrew the *it*. 8)

If your pilot volume is small enough, a schrader is enough to pilot your piston.

very very nice build really impressed by the simplicity, good job