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.25 Air rifle, Breech loaded, rifled barrel

Built a pneumatic 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: Gun Freak » Mon Jun 27, 2011 10:27 pm

In my experience changing the piston mass doesn't effect the numbers much in GGDT.
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Unread postAuthor: saefroch » Mon Jun 27, 2011 11:12 pm

Generally it doesn't, unless you're using an absurdly heavy piston, like the solid steel one I used for a while. However, it is of worth to note that piston mass becomes less and less significant as chamber pressure increases.
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Unread postAuthor: airheadnoob » Mon Jun 27, 2011 11:19 pm

go with this sleeve valve like jackssmirkingrevenge said.
i don't think you need that much air for one shot,
http://www.ebay.com.au/itm/16mm-Screw-T ... 055wt_1141
thats the same place you got your qev from,
i paid almost double for a sleeve and a qev like yours.
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Unread postAuthor: cane toad » Tue Jun 28, 2011 12:12 am

Here's a (very!) rough concept drawing, the bottle becomes the stock attached to the slide valve and the firing chamber is made much smaller.



JSR I've drawn on your picture, is this right? What effect does the trigger have? Does it fill the firing chamber? If so how does it pilot? I'm assuming I still use the qev as is?
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 28, 2011 12:24 am

cane toad wrote:JSR I've drawn on your picture, is this right?


Yes.

What effect does the trigger have? Does it fill the firing chamber? If so how does it pilot?


The yellow bit on the slide valve is the part which slides. The slide, as it were :)

In the forward position (trigger at rest), it connects the pilot area of the QEV to the main chamber. This fills the pilot area and the firing chamber.

In the rear position (trigger pulled), it shuts off the air supply from the main chamber, and opens the pilot area to the atmosphere. This pilots the valve, emptying the firing chamber.

Release the trigger (you have to add a spring somewhere) and the slide goes back to the rest position, filling the firing chamber and allowing the cycle to be repeated.

I'm assuming I still use the qev as is?


Yes
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Unread postAuthor: cane toad » Tue Jun 28, 2011 1:08 am

Thanks for explaining that, JSR. Would the valve airheadnoob linked to above work in this setup?
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 28, 2011 1:12 am

If the thread matches your QEV, you should be fine.

Here's an example of a QEV/slide valve launcher: http://www.spudfiles.com/forums/semi-au ... 22363.html
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Unread postAuthor: Lockednloaded » Tue Jun 28, 2011 12:21 pm

cane toad wrote:Lockednloaded - Thank you. Yes it has more power than the last one. You make an interesting point, I know the chamber is way too big (not a deal breaker for me since it was a scrap part ie free and I'm filling with a compressor) however when I tried a smaller chamber (using a length of hydraulic hose like my last gun) I seemed to lose a lot of power. I haven't done any further testing in that regard, ie what the optimal chamber size would be.

On your last one, the chamber volume had to be bigger to compensate for the low flow, slow valve. Now you have a high flow high speed valve that can use a smaller chamber more efficiently. Also, the really gain in power from shrinking the chamber comes from being able to pump it to higher pressures, twice the pressure generally results in four times the velocity*
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Unread postAuthor: CollegeGuy » Tue Jun 28, 2011 3:48 pm

Pretty nice gun, but one big question remains - How did you exactly rifle a STEEL(!) barrel? How did the tool look like is it still usable? Pictures of the rifled barrel(If you don't bother to take the barrel off, of course) and pictures of the rifling tool would be great.
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Unread postAuthor: cane toad » Tue Jun 28, 2011 6:42 pm

Lockednloaded - Thanks for the explanation.

CollegeGuy - My mate has pinched the rifling tool but I'll try and describe it. Basically it's made from a piece of tool steel, which is extremely hard steel used to make cutting edges for metal lathes. We used a piece this size http://www.ebay.com.au/itm/6PCE-3-L-1-4 ... 5199a0d747 but we had to cut it down a fair bit. A piece this size might fit a 1/4" barrel http://www.ebay.com.au/itm/7PCE-3-L-3-1 ... 3f0a91cacf I'm not sure, might be too small.

We ground the corners down on an angle (hard to describe) and cut the last 1/2" off the end of the tool steel to use as the rifling tool. So we ended up with a piece of tool steel 1/2" long with angled egdes that was just a bit ovresized to fit in the barrel. Then we just tapped the piece through the barrel with a thin steel rod. As it grips the barrel on the way through it turns itself.

There is probably a million ways to do this, this was pretty quick. Soory for the horrible explanation. A picture really would explain it better. I'll try and get hold of the piece we used.

Thanks for the comments/questions.
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Unread postAuthor: CollegeGuy » Thu Jun 30, 2011 4:21 am

Thanks for the reply! I can pretty much imagine how it looks like so don't worry about that but a picture of the rifling tool or the rifling would be great.
In this forum there are many guns with rifled barrels but no one has built a gun with a steel rifled barrel(as far as I know) which, in my opinion, won't wear out as quickly as a copper barrel.
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Unread postAuthor: cane toad » Thu Jun 30, 2011 11:03 pm

Yeah I kicked myself for not taking a picture of the rifling while the barrel was off, but it's a pain to keep pulling the gun apart because I have to sight the scope in again and again. If I do have to pull the barrel off at some point I'll make sure to take pics. I agree that a steel rifled barrel should last longer than a copper one.

My mate is going to use a stainless steel barrel on his (when he gets around to making it). I'll try and get photos of the rifling on that one, it should look nice. As for the rifling tool, if I can get him to bring it back in to work I'll put a photo up.

Thanks again.
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Unread postAuthor: CollegeGuy » Sat Jul 02, 2011 8:20 am

If it bothers you to take the barrel off then don't worry, I'll be waiting! :wink:
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Unread postAuthor: ansen6606 » Tue Jul 19, 2011 10:44 am

hey man what type of valve did u use as trigger,where can i buy it online?? help me please im using the same system as u did
thxx
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Unread postAuthor: Gun Freak » Tue Jul 19, 2011 10:44 am

It's a blowgun, you don't need to buy it online, get it in a store.
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