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"In the world of spuds today"

A place to ask general spud cannon related questions.
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Unread postAuthor: deathbyDWV » Sun Jul 18, 2010 3:04 pm

Go on YouTube and search for paintborg. He has a video called something like how to make a custom sight riser. I think that'll show what you need... :wink:
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Unread postAuthor: SpudBlaster15 » Sun Jul 18, 2010 4:06 pm

ITWOST, I finished up a new steel piston for my hybrid valve, which should allow me to reach 10X without worry of the piston imploding.

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Unread postAuthor: SpudFarm » Sun Jul 18, 2010 4:37 pm

Nice piston, I use the same type in my pneumatic. The problem in your case might be the rod bending after a few shots.

Post some videos of 10x shots. I would like to see it:)
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Unread postAuthor: Ragnarok » Sun Jul 18, 2010 5:01 pm

qwerty wrote:Can i ask how you managed to epoxy (I'm guessing) the Dovetails on to what looks like 15mm copper?

Oh, that's easy. I cut the dovetail from copper and used a type of epoxy that's got tin in it - it's normally sold in wire form, and you have to use a blowtorch to cure it.

I learnt from an earlier mount that regular epoxies don't work very well for the job. (The other thing I learnt from that earlier mount was that it was far too low, which is why the new version has been mounted about 25mm higher.)

Annoyingly, it looks like the final weight is going to be about 5.5 kg. I was hoping for an upper limit of 5 kg, but I can't see how to lose much more weight without making sacrifices that I'd rather not.
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Unread postAuthor: Mr.Sandman » Sun Jul 18, 2010 5:16 pm

@ Qwerty, what you could do is take some 4mm thick steel bar and file the sides into slopes, then glue it down onto your chamber. Makes a great diy dovetail mount. ITWOST, I ordered more parts for LRR and they should arrive next week.
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Unread postAuthor: Gun Freak » Sun Jul 18, 2010 5:51 pm

Kind of like what I did on my M16, just posted new pics so you can see what I'm talking about.
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Unread postAuthor: SpudBlaster15 » Sun Jul 18, 2010 8:22 pm

SpudFarm wrote:Nice piston, I use the same type in my pneumatic. The problem in your case might be the rod bending after a few shots.


That's one of the reasons I chose to use a dual spool setup to stabilize the piston in its slide. With this setup, the piston cannot distort or tilt significantly, which should limit the maximum lateral stress on the rod to an acceptable value.

Post some videos of 10x shots. I would like to see it:)


I'm probably going to design and build a tripod to help deal with the recoil energy that will inevitably be produced by heavy rounds at 10X mixes, so there may not be video for a couple days. However, I'll be sure to shoot something impressive once it's done. DYI suggested an attempt to fire a hardened steel center punch through 3/8" steel plate, and if I get around to that, it should be interesting.
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Unread postAuthor: Technician1002 » Sun Jul 18, 2010 10:59 pm

My concern is the grooves are too shallow and the o ring is too tall. The side force on the o ring may try to blow it past the edge.

Just how large is the piston without the o rings in relation to the ID of the cylinder it goes inside?


The side of the o ring should land firmly on the side of the groove, not hang out in space unsupported.
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Unread postAuthor: SpudBlaster15 » Sun Jul 18, 2010 11:57 pm

Technician1002 wrote:Just how large is the piston without the o rings in relation to the ID of the cylinder it goes inside?


The measured value of the piston's major diameter is 2.00", while the ID of the pipe it slides in is 2.07". The minor diameter of the o-ring groove is 1.75", and the o-ring thickness is 0.188". It's designed to be a high compression seal, which is why the depth of the groove appears to be insufficient.

When assembled, the o-ring undergoes ~15% compression; and the gap around the large washer is only ~0.035", which corresponds to about 10% of the groove depth. According to the texts I've read on the subject of o-ring groove design, this is within the ideal range.

The side of the o ring should land firmly on the side of the groove, not hang out in space unsupported.


As said above, this is a high compression seal. The groove should be wider than the o-ring to allow for lateral expansion when the pipe's internal surface compresses the seal. From what I've read, the exact amount of required clearance varies from about 20 - 40% of the o-ring diameter, depending on the exact degree of compression the seal undergoes.
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Unread postAuthor: Ragnarok » Mon Jul 19, 2010 9:01 am

I have a piece of rather leaky pipe.

Image

With no less than a hundred 6mm holes, it's due to become a barrel porting attachment. Previous testing has shown me that porting the barrel is one of the best things* you can do to improve the accuracy of a smoothbore spudgun. (The other big thing being a stiff barrel, which being a copper barrel, it already is.)

*Not including improvements to projectiles.

The total flow area is about 28.3 square centimetres, which is total overkill, given that the barrel's flow area is only 3.2 sq. cm. Should get rid of muzzle blast quite nicely. But of course, the proof of the pudding is in the eating, so we'll have to wait for testing to see how well it works.
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Unread postAuthor: Crna Legija » Mon Jul 19, 2010 9:30 am

Hahahah the other day my dad put new floor boards in the kicthen. He just missed the beam and hit the water pipe and from that point keep going on in line with the first nail, keep hitting the pipe for like 3m.
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Unread postAuthor: Mr.Sandman » Mon Jul 19, 2010 12:49 pm

How did you file out the middle most holes so that there were no burrs? It would seem that you needed and incredibly long file.
Does the shape of the ports determine the effectiveness of the muzzle break? For example, If you had drilled the same amount of holes, except in a spiraling fashion, would that have any added advatage over the current position of the holes?
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Unread postAuthor: jackssmirkingrevenge » Mon Jul 19, 2010 1:08 pm

-_- wrote:Hahahah the other day my dad put new floor boards in the kicthen. He just missed the beam and hit the water pipe and from that point keep going on in line with the first nail, keep hitting the pipe for like 3m.


:D

He must have been delighted.

Does the shape of the ports determine the effectiveness of the muzzle break? For example, If you had drilled the same amount of holes, except in a spiraling fashion, would that have any added advatage over the current position of the holes?


Image

The VSS has spiral porting which follows the rifling grooves, apparently this makes the suppressor more effective. In terms of acting as a muzzle brake, I doubt it would affect performance. If what you want is an air stripper to help accuracy, you need a more efficient design like this commercial model

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Unread postAuthor: SpudBlaster15 » Mon Jul 19, 2010 1:11 pm

Mr.Sandman wrote:How did you file out the middle most holes so that there were no burrs? It would seem that you needed and incredibly long file.


I imagine he inserted a small diameter round file through the holes at an acute angle to the pipe, then filed a slight bevel on the inner edge to remove the burr.

Does the shape of the ports determine the effectiveness of the muzzle break? For example, If you had drilled the same amount of holes, except in a spiraling fashion, would that have any added advatage over the current position of the holes?


In practice, I doubt there would be any appreciable difference between different porting designs. The goal is to quickly vent as much of the air as possible to the atmosphere, and for that, the only significant design criteria is high vent surface area. Staggered, linear ports achieve this nicely, while maintaining rigidity of the pipe.
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Unread postAuthor: Ragnarok » Mon Jul 19, 2010 2:26 pm

Mr.Sandman wrote:How did you file out the middle most holes so that there were no burrs? It would seem that you needed and incredibly long file.

Easy. Needle file through the holes themselves - pretty much as SB15 says.

However, it does help that I have a piece of 20mm steel rod that I could push back and forwards through it to help dislodge any burrs.
The same 20mm rod came in useful as a way of telling when I was actually done with cleaning the burrs out - until it would drop freely through the pipe, it clearly wasn't done.

Same thing applies to any other piece of pipe. If it won't pass through cleanly, I need to work out why. In the past, a common problem was that the end of the pipe had been pinched, which is why I don't use pipe cutters any more. I find I get better results with a hacksaw and file.

Does the shape of the ports determine the effectiveness of the muzzle break?

Well, it's not so much a muzzle brake. It will reduce recoil a certain amount (because any gas going sideways out of the ports isn't going forwards out of the muzzle), but reduction of recoil is not one of the design goals.

The purpose is just to dump as much pressure from the barrel as quickly as possible to reduce the muzzle blast.

I've tinkered with designs along the same line as what Jack's linked to, but my discoveries have largely come down to being that something designed for an air rifle using a few cc of gas (which is mostly expanded when it reaches the muzzle) does not work quite as well when dealing with a launcher that uses multiple litres of air a shot.

So, this is something with a bit more guts to it.

For example, If you had drilled the same amount of holes, except in a spiraling fashion, would that have any added advatage over the current position of the holes?

Aesthetics maybe*, but not performance wise. As it is, SB15 has it pretty much right again - I want high vent area, but rigidity as well.

*I had considered 8mm holes in just two axes. I could get about the same flow area, possibly even slightly more by making it only 25mm between holes rather than 30mm (although it's only 17mm between the "staggered holes" - they're deliberately laid out in equilateral triangles).
That was mostly because the gas coming out of the porting in an X pattern looks quite cool, whereas in 4 axes, it's not distinct any more.

However, experience has shown me that drilling 8mm holes in copper often results in rather messy holes.
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