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Bolt action coaxial?

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Bolt action coaxial?

Unread postAuthor: sputnick » Thu Jan 22, 2009 8:01 pm

Hey everybody, I was thinking about a way to clip feed a coaxial, and I came up with this,

If it has been done, sorry, I did not know, but I would LOVE to see pictures

This design is for a bolt action coaxial gun mechanism, this is possible by putting the barrel straight through the piston, and then to compensate for the pressure area difference, there's a tube at the front to limit the area the pressure can push it backwards, as well as a spring behind the piston.

The air passes through holes drilled into the barrel under the piston, and then flow past the small rod on the bolt, used for pushing the ammo past the holes, but keeping the bolt back so as to not restrict the air.

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So what do you think? workable? worth trying? worth looking at?

any feedback would be great!
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Unread postAuthor: MrCrowley » Thu Jan 22, 2009 8:18 pm

Looks like it'd be far more hassle then it's worth. You'd need quite a few 100% o-ring seals and the flow doesn't look terrific either. It probably could work, but i'd just stick with a ram-rod then go through that.
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Unread postAuthor: sputnick » Thu Jan 22, 2009 8:19 pm

I suppose, but you must admit theres a cool factor to it too, it would be awesome for paintball...
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Unread postAuthor: starman » Thu Jan 22, 2009 8:24 pm

Looks great to me! The only thing I can see off the bat is the bolt needing an O-ring fit around it in the barrel to keep the air from slipping out during firing and out the back. I know, small amount, but not something you would want to happen.
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Unread postAuthor: daberno123 » Thu Jan 22, 2009 8:30 pm

It looks great on paper but without using something as precise as a lathe to make o-ring grooves it'll be leaking like none other. A little air always finds a way to get past o-rings no matter how hard you try.

Do you plan on actually attempting to construct this?
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Unread postAuthor: MrCrowley » Thu Jan 22, 2009 8:31 pm

It'd definitely be cool on large scale, keeping to the artillery type of loading. No reason it shouldn't work, but if you think it's worth the hassle I don't see why it can't be done.
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Unread postAuthor: starman » Thu Jan 22, 2009 8:38 pm

Oh yeah, getting those internal O-ring grooves milled on the inside of your piston is going to be a real bear without a lathe.

Also, consider square air holes in your barrel. The round ones will restrict the air flow at beginning of the piston travel. Closely spaced square ones will at least offer the maximum airflow that could be expected in this configuration.

BTW, nice drawings!
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Unread postAuthor: sputnick » Thu Jan 22, 2009 8:40 pm

Well, I realise that O-rings are a hassle, but I could find ways to make it more airtight, by making sloght variations in the pipe diameter,

Also for a lathe, I don't have one, but a drill in a vise with certain tools works better than many would think, not perfect, and guetto to be sure, but workable with time to kill.

I currently have very little money to do anything with, but I am looking to get a job after exams, and after that I will be able to build more of what I design, So if I get the money, this is high on the priority list, It would be great for a paintball sniper, just extend the barrel past the chamber by a couple feet, and put a stock on it, and you got a perfect sniper...
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Unread postAuthor: MrCrowley » Thu Jan 22, 2009 9:19 pm

starman wrote:Oh yeah, getting those internal O-ring grooves milled on the inside of your piston is going to be a real bear without a lathe.

Could always just stick the o-rings on the outside of the barrel :)
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Unread postAuthor: daberno123 » Thu Jan 22, 2009 9:24 pm

Telescoping brass tubes could aid in making some of the seals more bearable. I've never worked with it personally but I hear it makes an airtight seal. Look it up on McMaster.
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Unread postAuthor: starman » Thu Jan 22, 2009 9:29 pm

MrCrowley wrote:
starman wrote:Oh yeah, getting those internal O-ring grooves milled on the inside of your piston is going to be a real bear without a lathe.

Could always just stick the o-rings on the outside of the barrel :)


Yeah you could, there's just not a lot of thickness in the SDR21 1.5" wall(assuming a golfball gun here) to mill grooves into.
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Unread postAuthor: sputnick » Thu Jan 22, 2009 9:31 pm

I actually assume paintball gun here, so even smaller, but somewhat thicker (3/4 inch cpvc)

Hey, anybody noticed that 1/2 inch pvc is actually 3/4 inch? and 3/4 inch pvc is 1"??
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Unread postAuthor: daberno123 » Thu Jan 22, 2009 9:35 pm

Also, have a look at the only other breech loaded coaxial (that I can think of): Clicky!

Its similar to your design except he's moved the valve above the chamber and eliminated some of the seals of your design. He still mentions using a lathe for it though.
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Unread postAuthor: sputnick » Thu Jan 22, 2009 9:37 pm

I was trying to make it like a real bolt action rifle, and that just has the airtank wrpaed around the barrel,

I don't really see that much of a connection except for loading procedure
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Unread postAuthor: MrCrowley » Thu Jan 22, 2009 10:13 pm

starman wrote:
MrCrowley wrote:
starman wrote:Oh yeah, getting those internal O-ring grooves milled on the inside of your piston is going to be a real bear without a lathe.

Could always just stick the o-rings on the outside of the barrel :)


Yeah you could, there's just not a lot of thickness in the SDR21 1.5" wall(assuming a golfball gun here) to mill grooves into.
'
Spose you could always sleeve said SDR21 with Sch80 where the o-rings are.
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