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Smooth bore or Rifled

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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Smooth bore or Rifled

Unread postAuthor: john bunsenburner » Tue Nov 11, 2008 2:05 pm

Again and again we are all put before the choice; Smooth bore or rifled barrels for our newest gun. Now I am still in the act of building my first sniper rifle, I found a totally new valve for it which i will try out...Any how I wan my gun to fire very small projectiles about 5-8mm. The thing that I still have to do is get my self a barrel so I ask you, spudfiles members, what experiences and recomendations do you have about barrels, how badly do they affect the accuracy of a gun. What do you recomend me to do? I am anxious to hear everybody^s commenst/recomendations.
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Unread postAuthor: Bando_Red » Tue Nov 11, 2008 2:11 pm

I'm a noob to spud guns and I've been curious about rifled barrels as well.I remember seeing a DIY rifling article once somewhere,but it seemed to have very inconsistent results.Is it just me or are spud and air guns more complex than real firearms?
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Unread postAuthor: john bunsenburner » Tue Nov 11, 2008 2:23 pm

They are difinately but also they are safer. I have built both but i only nearly lost my hearing when firing the black powder one. And it makes me very happy to see i am not the only person here who wondered about the barrel bore they use.
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Last edited by john bunsenburner on Tue Nov 11, 2008 2:25 pm, edited 1 time in total.
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Unread postAuthor: Pilgrimman » Tue Nov 11, 2008 2:25 pm

I think the main idea with rifling is to have a projectile that fits well enough for the projectile to "grip" the grooves in the rifling. If the rifling doesn't contact the projectile, the rifling will have little effect. I suppose you could put fins on your projectile. I'm not an expert by any means in rifling, however. I would advise you to do some research about the science behind it, then try to implement the idead into a spudding context. I hope it comes out good, whatever you decide to do! :D
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Unread postAuthor: john bunsenburner » Tue Nov 11, 2008 2:27 pm

How about rifeling the bullet(i am making my own pellets so it works). The idea with rifeling is to make the projectile turn giving it more accuracy. Tell my if my idea works.
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Unread postAuthor: jackssmirkingrevenge » Tue Nov 11, 2008 3:46 pm

john bunsenburner wrote:How about rifeling the bullet(i am making my own pellets so it works). The idea with rifeling is to make the projectile turn giving it more accuracy. Tell my if my idea works.


No it doesn't.

The easiest solution is to keep the smoothbore barrel and make projectiles with a forward centre of gravity to retain stability. It's true that "drag stabilisation" costs some forward energy, but when you consider rifled projectiles, they are also taking some of that energy to spin the projectile so it still works out.

The best thing to look at for inspiration is either ammunition made for modern tanks or slugs made for shotguns. In the latter category, I think the easiest and most effective to replicate is the foster type slug, a cylindrical bullet shape with about 80% of its base hollowed out (first slug on the right)

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Unread postAuthor: psycix » Thu Nov 13, 2008 2:32 pm

Jack, the fact that that one rifled round failed doesn't mean that all will.
Maybe it went fast enough and had such a geometry that turbulence canceled the effect.
Also it may have failed just due to that it was so heavy that the forces which made it rotate were not high enough to give it a noticable rotational speed (yet).
Also, you can see that the smoke travels along with the projectile, which means that there is an airflow coming out of the barrel, which made the projectile not feel any air resistance yet, as the surrounding air moves just as fast.



True is, that when rifling the barrel OR the projectile, you will lose velocity and thus penetration power due to kinetic energy being lost and rotational energy gains.

The largest drawback of rifling your barrel is, how the heck are you planning to do that? One will need to construct a large tool just to rifle that barrel.

The easiest way for accurate ammo is to make sure that the center of mass is in front of the center of drag forces.
So: heavy stuff in the front and light materials, fins, hollowing out or a tail in the back.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 13, 2008 2:47 pm

psycix wrote:The easiest way for accurate ammo is to make sure that the center of mass is in front of the center of drag forces.
So: heavy stuff in the front and light materials, fins, hollowing out or a tail in the back.


The rifled projectile in the video is a Brenneke slug like this one:

Image

It achieves stabity through the forward cenre of gravity thanks to the lightweight fibre tail.

From Wikipedia:

The Brenneke slug was developed by the famous German gun and ammunition designer Wilhelm Brenneke (1865–1951) in 1898. The original Brenneke slug is a solid lead slug with fins cast onto the outside, much like a rifled Foster slug. There is a plastic, felt or cellulose fiber wad attached to the base that remains attached after firing. This wad serves both as a gas seal and as a form of drag stabilization, much like the mass-forward design of the Foster slug. The "fins" impart little or no spin to the projectile; their purpose is to decrease the bearing surface of the slug to the barrel and therefore reduce friction and increase velocity.


This may well mean that it could work at subsonic velocities, but the "rifling" would have to be much bigger, until you effectively have a finned projectile.
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Unread postAuthor: Bando_Red » Sat Nov 15, 2008 12:50 am

So lets say you get a barrel from a .22 caliber rifle,and then use .22 caliber pellets in it? :?
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Unread postAuthor: Gippeto » Sat Nov 15, 2008 1:09 am

Rifle bores measure .223"-.224"

Airgun bores are nominal .217"-.218".

The airgun pellets might "bump" up to bore size if you have enough oomph, but the rifling rate in the barrel was designed for heavier slugs, and accuracy would suffer.

You could however buy an inexpensive barrel from Crosman, OR you could buy a really nice Lothar Walther barrel.

Those would work better. :)

For "spudding" type slugs, I have to agree with Jack, the foster slug is the way to go.

The molds can be as simple or complex as your tooling allows. :)
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Unread postAuthor: john bunsenburner » Sat Nov 15, 2008 3:30 am

The mold is alli right? What else could i use?, how many slugs can i cast in lets say one hour? How much lead is needed for 100slugs?
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Unread postAuthor: Gippeto » Sat Nov 15, 2008 10:12 am

Yes, it is aluminum.

"Way back in the day", bullet molds were cast from iron. Smoking the mold with a match was the method of providing a "release coating".

If you use a cold steel bar, the lead might not bond to it, but I've not tried that so I cannot say for sure.

I would stick with aluminum.

Speed of casting is dependant on too many variables to get a round/hr rate that is accurate. That mold gets pretty hot. (To the point where leather welding gloves start to smoke.)

That slows me down. :lol:

How big are your slugs? The one in that mold is 830grain (53.9g). There are 7000 grains to the pound, or 15400 grains to the kg.

100 X 53.9g =5390g

That's roughly 2 1/2 pounds of lead casted.
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Unread postAuthor: john bunsenburner » Sat Nov 15, 2008 10:45 am

So they do weight quite a bit... Thank you any how, ill try it as soon as my gun is ready, What did you melt your lead with?
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Unread postAuthor: Gippeto » Sat Nov 15, 2008 11:12 am

I have a cheap stainless steel pot I use with a single burner propane stove.

I use a cheap stainless steel soup ladle to pour the slugs.

Work with lead OUTSIDE. The fumes are toxic.

And don't forget to wear protective clothing. Heavy (and long) gloves and safety glasses. Cover exposed skin.

For your own safety, you need to take molten metal VERY seriously.

Don't get sloppy with it, or you WILL get burned.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 17, 2008 3:26 am

Bando_Red wrote:So lets say you get a barrel from a .22 caliber rifle,and then use .22 caliber pellets in it? :?


Air rifle, of course, as Gippeto pointed out. That would work, but you need high pressures for decent power.

Also, beautiful fosters there :D
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