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BACH – Bolt Action Cartridge Hybrid

Built a hybrid cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: daccel » Sun Dec 28, 2008 12:10 pm

I found three layers burst at around 40 psi, so I tried ten and that held at 120. But maybe it was how the disk was held, because if you look at the picture you can see how sharply it crimps the disk. Maybe it's getting weakened at that point. Anyone tested smaller disks like this before?

Metering is manometric. Filling is through a schrader epoxied in a 1/4x3/8 bushing which threads into a turned down 3/8 coupling which is epoxied into the back of the cartridge.
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Unread postAuthor: ALIHISGREAT » Sun Dec 28, 2008 12:16 pm

and then do you have the spark jumping to the chamber wall?
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Unread postAuthor: Dave_424 » Sun Dec 28, 2008 3:41 pm

Hey just to clarify on the birst disk

If 3 disks burst at 40psi

Then one disk is 13.33333333333333333 psi

the 10 disks you tried would have burst at 133.333333333333 psi

What x mix are you going to run it at?

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Unread postAuthor: daccel » Sun Dec 28, 2008 4:59 pm

There is no spark, it is several strands of steel wool that melt, but yes they connect with the chamber wall.

I know that the burst pressure of those ten disks was just above filling pressure, but I wanted to start low and work up.

Ended up not actually using the aluminum foil, because the o-ring was getting squished down into the chamber and not sealing well. Maybe a different size or a washer instead would work. For now I used tape.

And it works!!! See video and pictures below. Still having problems with consistency due to sealing and ignition, but I managed to get a few shots off.

8.5x mix with an 8.8 gram projectile
[youtube]http://www.youtube.com/watch?v=A9hTlbkbWZg[/youtube]

8.5x mix with a 25.9 gram projectile
[youtube]http://www.youtube.com/watch?v=ThTJVpDcRBc[/youtube]

I was expecting it to be louder, but I guess with a .14 C:B ratio inc. suppressor the pressure is pretty low by the time it exits.

Looks like I need to find a way to get the foil to work because the tape is too tough.
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Attachments
tapebd.jpg
8.8g ammo.jpg
8.8g ammo.jpg (12 KiB) Viewed 2770 times
25.9 cartridge.jpg
25.9 cartridge.jpg (29.14 KiB) Viewed 2770 times
8.8 exit.jpg
board.jpg
Top one is from 8.8g through can, bottom is 25.9g.
board.jpg (12.54 KiB) Viewed 2770 times
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Unread postAuthor: ALIHISGREAT » Sun Dec 28, 2008 6:16 pm

nice work! wouldn't have been my choice of ignition... but it works!
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Unread postAuthor: Dave_424 » Sun Dec 28, 2008 6:19 pm

Just wondering, the shot on the can, is it a dent or did the projectile pass through leaving a flap of the can?

I think you need to find a better birst disk material, the way that piece of tape burst meant that it was restricting flow
You should try the aluminium foil again, it gives alot better and cleaner break

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Unread postAuthor: ALIHISGREAT » Sun Dec 28, 2008 6:24 pm

i reckon the tape must have heated up and stretched out or something...
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Unread postAuthor: Dave_424 » Sun Dec 28, 2008 6:27 pm

Yeah, I think that the barrel diameter should be reduced, I think that will yield better results, maybe to a real calibre (or closest) diameter and use the bullets bought from reloading shops
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Unread postAuthor: Sticky_Tape » Sun Dec 28, 2008 6:30 pm

What is the pressure you can get with a 8.8x mix? Nice gun I like.
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You can tell how awesome a cannon is by the pressure used.
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Unread postAuthor: LCTChamp » Sun Dec 28, 2008 6:33 pm

I agree with Dave the barrel diameter needs reduced. With an 8.5X mix you should be getting some crazy damage, and it doesn't look like you are. I would suggest a .22 pellet barrel. I understand it if you don't want to change things, but I think that will give the best results.
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Unread postAuthor: Dave_424 » Sun Dec 28, 2008 7:03 pm

A way to gure the o-ring being pushed into the chamber is to add a washer after the aluminium foil

The way that the fitting is cut, means that it hasn't got a flat face, if you add a washer (Remember to have as big hole in the middle as you can)
which will stop the o-ring being pushed into the chamber

I think that you should also add a washer behiend the o-ring which I think will help in sealing aswel

Dave
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Unread postAuthor: daccel » Sun Dec 28, 2008 8:29 pm

Yeah I may switch ignition sources. The inconsistency is frustrating.

It cut a flap but it didn't pass through because it was tight against the board, ended up inside the can.

Theoretical pressure of 8.5x is 970psi, which with an 8.8 gram projectile is 95 ft/lbs and 560 fps. However, I don't know what pressure the burst disk is failing at.

I think the burst disk is having more of an effect than the barrel diameter, because I used a piece of aluminum from the can as a disk with a piece of tape to help seal and it seemed about twice as powerful. Also have to remember it's only a 1 cu in chamber. But a smaller barrel would increase penetration probably. And I found a place locally I can get a 24" .22 crosman barrel for $22, which would open the door to manufactured ammo. So it is something to consider.

That's a good idea about the washer, I'll try it out if the current method stops working.
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Unread postAuthor: sputnick » Sun Dec 28, 2008 8:31 pm

Oh Wow, that is very nice looking, I VERY much like the bolt action, it acts like a real firearm, and no fussy pneumatic valve. I don't really understand how you can make a projectile fire at a decent velocity from a tank that is smaller than the ID of the barrel, bearing in mind that i have no knowledge of hybrid launch systems, and the power they produce.

However, despite these little nuances, this is a phenomenal looking gun, and it is making me seriously consider building something like this. If i can figure out a way to make a hammer hit a pin at the rear to pierce a disc, i will design it and likely build it, i can only hope it will look as good as yours :wink:
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Unread postAuthor: LCTChamp » Sun Dec 28, 2008 8:48 pm

Sputnick- It fires at a decent velocity with a small chamber because it is a hybrid. Hybrids are much more powerful than any pneumatic or regular combustion. There is no need for a hammer and pin to pierce the disc, the pressure generated from the ignition of fuel bursts the disk. I would suggest you do a lot more research before attempting a hybrid launcher. Look at the spud wiki to help you understand the concept of hybrids.

daccel- You could always have interchangeable barrels and use both.
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Unread postAuthor: sputnick » Sun Dec 28, 2008 8:59 pm

I am not looking to build a hybrid, i was thinking purely pneumatic, with a mechanical disc piercer, something that could punch out a large circle, and a barrel that is much smaller than the chamber, for two reasons, one, the reduced area would restrict the chamber sliding into the barrel, and also mean i could have a larger chamber to barrel ratio.
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