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Rifling machine

A place to ask general spud cannon related questions.
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Unread postAuthor: elitesniper » Wed Jan 23, 2008 8:39 pm

well the number two blue shot looks like it did well lol.
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Unread postAuthor: judgment_arms » Wed Jan 23, 2008 8:52 pm

Blue was the smooth bore, I’ll admit that 2 shots wasn’t a good comparison, but I felt the test should be done at a range greater than 10 yards and with the gun clamped down for a more consistent grouping so I stopped after that.
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Unread postAuthor: Ragnarok » Wed Jan 23, 2008 9:07 pm

judgment_arms wrote:If it is that’s news to me, in my two years of research I’ve always heard that rate of twist is the pitch of the rifling, and not dependent on velocity. but thing again I could be seriously mistaken.

What I should have said is "ideal" rate of rifling.

The Greenhill equation, the most famous rifling equation contains a coefficient that is swapped around depending on velocity:
C * B<sup>2</sup>/L * SQRT(D/10.9)

C is the Greenhill coefficient.
B is the bore in inches.
L is the length of the projectile in inches
D is the density of the projectile in, weirdly, g/cm<sup>3</sup>

Result is 1 turn in X inches.

When the equation was first developed, you would normally at mid range bullet speeds (~1500 to ~2500 fps) use 150 as the coefficient, but at higher speeds than that, it was recommended that you use 180. Lower velocities need a lower value. However, it's now suggested that the coefficient is entirely replaced with 3.5 * sqrt(Velocity)
The Greenhill formula is a little dated, these days there are better ways of handling it, but it will still give us a good estimate.

So, a 300 fps paintball ideally needs a twist rate of one turn in 14 inches, a 600 fps PB needs one turn in 20, and a 900 fps PB one in 24.

As you can see, it's heavily velocity dependent. In fact, that's a slightly simplified equation, rifling is even affected by the air density. Your 102" twist seems a little shallow based on those numbers, although it is perfect if you've got a muzzle velocity of 16,000 fps.

Clever way of handing the marking of the "die" though. I hadn't thought of that.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: sinper2006 » Wed Jan 23, 2008 9:17 pm

lol that is simple. could you plz send me a diagram coz i need to build one to rifle 8mm and 6mm aluminum.
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Unread postAuthor: sjog » Wed Jan 23, 2008 9:24 pm

Rifling will not work on GB's or marbles.
Spuds will work great. Some one will take video of spiraling spud in the future, I hope!
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Unread postAuthor: Ragnarok » Wed Jan 23, 2008 9:25 pm

sinper2006 wrote:lol that is simple. could you plz send me a diagram coz i need to build one to rifle 8mm and 6mm aluminum.

Judge is trying to sell rifled barrels. I think he's already been more than generous enough just showing pictures, asking for plans is a bit like going to Coca-Cola and asking them for their secret recipe - to borrow a phrase that someone I knew used far too much.
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Unread postAuthor: daberno123 » Wed Jan 23, 2008 9:29 pm

Rifling will not work on GB's or marbles.
Spuds will work great. Some one will take video of spiraling spud in the future, I hope!


really i thought a potato would just rip right through the grooves, not imparting any spin,because they are so soft. Why wouldn't it work for spheres?
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Unread postAuthor: sinper2006 » Wed Jan 23, 2008 9:31 pm

i no i just trying well if if he goin to sell 6mm and 8mm aluminum barrels i would try to buy them but he not
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Unread postAuthor: ShowNoMercy » Wed Jan 23, 2008 9:31 pm

Because I think that the bullet has to expand into the grooves and therefore start spinning, whereas that would just deform a sphere. I think?
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Unread postAuthor: sjog » Wed Jan 23, 2008 9:37 pm

Marbles and GB's will roll in the barrel and not necessarily spin.
Black powder rifles that are rifeled most shoot a slug to spin the round.
ShowNo Mercy you got the idea.
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Unread postAuthor: sinper2006 » Wed Jan 23, 2008 9:39 pm

in my gun the main ammo is nails and ball sinkers. so it will help with the nails
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Unread postAuthor: sjog » Wed Jan 23, 2008 9:42 pm

No sense in using rifling Sniper2006
Shoot slugs or wads
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Unread postAuthor: sinper2006 » Wed Jan 23, 2008 9:48 pm

what about these?
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Unread postAuthor: ShowNoMercy » Wed Jan 23, 2008 9:48 pm

Why not just melt some lead sinkers down and make minnie rounds?
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Unread postAuthor: sinper2006 » Wed Jan 23, 2008 9:50 pm

me dad wont let me
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