BB sniper

[AngryChauncey]

I am building a .177 caliber bb rifle with a 0.5" piston valve and a 1.5' barrel (all metal by the way). My question is this: I was planning on making the chamber out of an 8" peice of 0.5" tubing, but i don't know if that is a big enough chamber to get the bb going at least as fast as a good pellet rifle. Also, my air compressor is a 5 gallon shop compressor that maxes out at 125psi.

[jackssmirkingrevenge]

i don't know if that is a big enough chamber to get the bb going at least as fast as a good pellet rifle

Have you considered getting a relatively cheap shock pump and using 300-400 psi? With smaller calibres especially pressure is much more important for power than chamber volume.

Just to give you an idea, I had modelled a virtual launcher on GGDT, using the same quantity of air but with ever decreasing chamber size (same diameter but shorter length) and therefore increasing pressure, and here's what I got:

20 inch chamber at 50 psi - 406 feet per second

10 inch chamber at 100 psi - 537 feet per second

5 inch chamber at 200 psi - 684 feet per second

2.5 inch chamber at 400 psi - 830 feet per second

1.25 inch chamber at 800 psi - 958 feet per second

0.625 inch chamber at 1600 psi - 1006 feet per second

[AngryChauncey]

This is a stupid question but what is a shock pump?

[jackssmirkingrevenge]

Something like this, keep your chamber volume to about 2 cubic inches and you can reach 400 psi easily.

[CpTn_lAw]

I should receive mine today!! can't wait!!
Thanks Jack for the numbers, I didn't think such a small chamber could manage that speed...(even if it's a GGDT prediction...)

[jackssmirkingrevenge]

Good luck with it

I've begun to look into this idea again, now that I can use my paintball tank as an 800 psi filling station I think a small cartridge about as big as one of these would give viable power and the possibility of automatic ejection. Using the construction methods I used in my pengun v2 they should be easy to "mass" produce too.

[CS]

...with mention of the NATO ammunition and all, got me thinking. Along the hybrid cartridge concept, what if you used a NATO cartridge? How do you get the fuel/oxy in there? Similar to a spool valve, the bullet would be used as the spool valve core. With the bullet 1/2 in the cartridge the valve would align, fully load the bullet and the valve would seal. Not sure the compression bullets have against there cartridge, but I suspect you'd get double digit mixes.

[10x Propane= 6.174 PSI]
[10x Oxygen= 30.723 PSI]
[Total=36.897 PSI]

[jackssmirkingrevenge]

I'm actually considering using a 7.62x51 cartridge, I have a couple of empties lying around not much success with a pressurised hybrid on a tiny scale from my part though

[CpTn_lAw]

GOd it's hard to pump past 250 psi on the shock pump!!! and the volume it pumps it so small XD

[jackssmirkingrevenge]

Seriously? How big is your chamber then?

[CpTn_lAw]

The chamber is a 3/4" tee, plus 3/4 => 1/2 => 3/8 => 1/4 " and a schrader valve epoxied in the 1/4 nipple.
I have an aching red-spot in my palm just pumping to 300 psi!!!

[jackssmirkingrevenge]

Mod it

[CpTn_lAw]

We have the same pump, i'm gonna mod it XD frickin hard, and the tee had a small leak i fixed... BRB with some pictures and feedback, in another topic lol

[dewey-1]

I'm actually considering using a 7.62x51 cartridge, I have a couple of empties lying around not much success with a pressurised hybrid on a tiny scale from my part though

To bad you are not in my area.
I could offer about 200 cartridges of .243 and .308 caliber.
Basically the same brass. The .243 is necked down.

[jackssmirkingrevenge]

Shame I'm wondering if they have enough volume for a 0.22 projectile though. They would certainly be ideal for a 3mm calibre cartridge but I'm not sure if going that low is worthwhile.