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Short question topic

A place to ask general spud cannon related questions.
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Unread postAuthor: ramses » Mon Jan 09, 2012 4:34 pm

I am looking for a repeater to replace a 9mm handgun. (9mm bore)

And you can find me a QEV good for 10ksi.

Airguns are not firearms in the US :D :D :D
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Unread postAuthor: warhead052 » Mon Jan 09, 2012 4:41 pm

Can I ask why you want 700 bar? I don't think you will find a material that will be small enough for a 9mm bore that will withstand that sort of pressure.
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Unread postAuthor: ramses » Mon Jan 09, 2012 5:25 pm

warhead052 wrote:Can I ask why you want 700 bar? I don't think you will find a material that will be small enough for a 9mm bore that will withstand that sort of pressure.


The mean pressure of an actual 9x19 cartridge is 35 ksi. The mean pressure of even a .22 lr has a mean pressure of 24ksi.

12 gauge shotgun is 11.5ksi. Those barrels are quite thin.

A .75" diameter 2024 T6 aluminum bar drilled out to .356 ~9mm would yield at 35ksi, leaving me with a safety factor of 3. 2024 is not all that strong, either.
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 10, 2012 12:46 am

high pressure valveless cartridges!

or maybe not, the force you would need to move a detent collar with that sort of pressure...

This is the most powerful repeating PCP pistol I can think of:

http://www.pyramydair.com/s/m/Evanix_Hu ... /961#sSpec

[youtube]http://www.youtube.com/watch?v=Vv2ZXTOFyIM[/youtube]

Basically a cut down rifle, and not as powerful as a small 22 rimfire pistol.

There's no way you can get 9mm muzzle energy from a pneumatic in a 9mm pistol sized package. Taking the above and boring it would would increase the muzzle energy considerably, but still not coming close to 9mm ft/lbs.

What's the point of it anyway, self defense? Why not an HPA BBMG? it would be the equivalent of a buckshot hose :D something like an even more ramped up version of Brian's Pnuzi ;)
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Unread postAuthor: Gun Freak » Tue Jan 10, 2012 6:04 pm

Here is my design for a hammer with an adjustable hammer weight and spring tensioner.

Excuse the flamboyant coloring :D
Red is 1/2" copper
from left to right
green:1/4" bolt
gray:1/2" washers
brown:wood with same ID as pipe
pink: spring
blue: 5/16" bolt and washer and coupling nut to adjust spring tention.

The excess green bolt will go through a nylon spacer that has a machine screw coming out the side to function as a bolt handle to pull back the spring (the machine screw will obviously come out a slot cut in the copper). I want to use the charging sleeve so that the screw coming out the side does not shoot forward upon firing, I can simple slide it back forward after I engage the hammer to the sear.

Not pictured: trigger/sear, charging sleeve (nylon spacer) and handle.

So I can tention the spring with the bolt, and adjust the hammer weight by adding washers. The left side of the bolt passes through the charging sleeve and hits the valve.

Thoughts? Improvements?

Also, where on the pipe would be optimal for me to position the sear?

(drawing not completely to scale-- I estimated some lengths so its a bit whack)
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Unread postAuthor: ramses » Tue Jan 10, 2012 9:36 pm

jackssmirkingrevenge wrote:What's the point of it anyway, self defense?


Then I must ask you what the point of ejecting brass cartridges is.

I realize that I can't get firearm performance; See above mean pressures.
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Unread postAuthor: Gippeto » Wed Jan 11, 2012 12:32 am

Gun Freak,

Striker travel should be 3/4" - 1 1/2" before contacting the valve stem. Would stay on the long side of this for a first time. You can always lengthen the striker to reduce effective stroke at a later time.

With your spring of choice, and adjuster screwed all the way in, you should "just" not be able to engage the sear. Back off the adjuster a 1/4 turn, and you should "just" be able to engage the sear. This will maximize your adjustable range.

Can use a spring guide on the striker side of things to increase effective striker mass if needed.

Striker bearing length should be no less than 1.5x diameter...more is better here as it will "run" smoother with less binding (greater consistency). Find something other than wood if you can.

Add a "locked" position to your slot in the aft position to provide a rudimentary safety without adding to parts count. :)
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 11, 2012 12:43 am

ramses wrote:Then I must ask you what the point of ejecting brass cartridges is.


Ah, so it's that kind of project :)

You could try replicating the Brocock cartridge, it's basically a forward acting QDV.

Image

By upping the pressure and calibre you're definitely get quite a bang. If I recall correctly they were filled to well below 200 bar or so, so there is hope for decent power with a bigger bore and moar pressure.

Brocock used to offer the "Para" based on the PPK for micro cartridges:

Image

Not enough power to cock the mechanism so it needed manual racking of the slide but you get the idea.

edit: interesting USP air cartridge conversion: http://translate.google.com.mt/translat ... id%3D39727
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Unread postAuthor: Gun Freak » Wed Jan 11, 2012 6:26 am

@Gippeto, thank you for the help! Drawing will be ammended after school.
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Unread postAuthor: Gun Freak » Fri Jan 13, 2012 11:07 pm

HDPE (5 bucks per sq ft) or UHMW (12 per sq ft) for my rotating hammer? Or I could just use pvc.
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Unread postAuthor: warhead052 » Fri Jan 13, 2012 11:20 pm

I would try pvc first, as a sort of "lets just see if it will work", then get the stronger plastic.
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Unread postAuthor: Gun Freak » Fri Jan 13, 2012 11:23 pm

Yeah that's probably a good idea.

What is y'all's opinion on this bushing? It says 200 psi, but it is brass... would it be safe at 500 you think?
http://www.mcmaster.com/#4429k471/=fso624
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Unread postAuthor: warhead052 » Fri Jan 13, 2012 11:38 pm

Yeah that should. Look at the rating for steam, why would it be 200psi at 74 degrees, when the rating for steam is 125 at 400 degrees? I may be wrong, but I think it will hold up.
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Unread postAuthor: evanmcorleytv » Fri Jan 13, 2012 11:38 pm

Gun Freak wrote:Yeah that's probably a good idea.

What is y'all's opinion on this bushing? It says 200 psi, but it is brass... would it be safe at 500 you think?
http://www.mcmaster.com/#4429k471/=fso624


It should be fine.. I've learned a lot from my local pressure engineers.
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Unread postAuthor: dewey-1 » Sat Jan 14, 2012 12:16 am

Gun Freak wrote:Yeah that's probably a good idea.

What is y'all's opinion on this bushing? It says 200 psi, but it is brass... would it be safe at 500 you think?
http://www.mcmaster.com/#4429k471/=fso624


Use this NPTF Hex Bushing
50785K63
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