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Rifled Barrel???

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Rifled Barrel???

Unread postAuthor: hyperspaz » Sat Apr 02, 2011 12:27 am

Okay, so I was thinking about how i could rifle a small bore pvc pipe. My first thought was to pull a drill bit through the barrel, but i immediately dismissed that idea due to rate of rotation of most drill bits; but recently i came across this drill bit, which seems perfect. From what i can tell from the pictures, i know it has three blades, and it looks to have a rotation rate of about 1 rotation per 8 inches (don't quote me on that).
Image
Oh and its an Irwin speedbor drill bit.

Tell me what you guys think. Thanks!
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Unread postAuthor: saefroch » Sat Apr 02, 2011 12:56 am

Rifled barrels have been discussed many times before, such as this thread, the general consensus is that most spudguns do not have the ability to make use of rifling, in that they cannot accelerate a projectile fast enough to compress it into the rifling and make it spin, and make any meaningful use of the rifling.
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Unread postAuthor: al-xg » Sat Apr 02, 2011 5:23 am

But then again not that many people have given it a fair try, this crude rilfing:
Image
Keeps solid lead bullets from tumbling past 80m (~88yd), making round impact holes and flat nosed bullets, up to now, without fail.
I am pretty sure the stable range is much greater but I haven't really done any high angle shots as it is very difficult to find the projectile.

I have tried rifling some copper with some reamers, but sadly their diameter was slightly too small and didn't leave much of a groove. The twist rate was the same as your drill bit. They are much easier to get stuck in the barrel though because of their length.
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Unread postAuthor: mark.f » Sat Apr 02, 2011 7:00 am

saefroch wrote:Rifled barrels have been discussed many times before, such as this thread, the general consensus is that most spudguns do not have the ability to make use of rifling, in that they cannot accelerate a projectile fast enough to compress it into the rifling and make it spin, and make any meaningful use of the rifling.


This is a simple matter of projectile design. If you're using PVC, you'd obviously be using potatoes with a rifled barrel, which are very capable of riding along rifling grooves. If you're using a harder metal, lead can be used, it's just a matter of how much pressure your gun operates at. Projectiles like pellets (which reduce the material being gripped by the rifling to two narrow areas front and back) and minié balls (which have a skirt that expands when fired to engage the rifling) can be used along with lower pressure guns.

@hyperspaz: what you're planning to do is pull what's called a "button" through your barrel. If you look at al-xg's thread, he does the same basic thing, but grinds his button from a bolt head.

Buttons will work for shallow, thin grooves like seen in al-xg's photo. For deeper or wider grooves, a button becomes much harder to pull through a barrel, which will require some ingenuity and lubrication.... something like a ratchet strap and lithium grease at best, or, if you're getting really ridiculous, a full length puller jig made from angle iron which allows attachment of a hydraulic jack at various points.

That drill bit may work if you are able to size it just so. Given that it's a woodworking bit, I doubt it comes in a vast selection of sizes, but there are some decent match-ups, like a 7/8" bit in 3/4" SCH-40 pipe (0.81" ID typically), or (for really shallow grooves), an 11/16" bit in 1/2" SCH-40 pipe (5/8" ID typically).
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