SpudFiles

jimmy101 wrote:the round may well be aerodynamically stable (and rifling isn't needed).

That's very debatable... it depends on your goal.

If you want to be able to fire rounds that will retain a good consistent ballistic coefficient and hit head on, rifling may not be necessary.

If your goal is accuracy and consistency of impacts, aerodynamic stability is far from enough. Most designs of airgun pellets are aerodynamically stable, but you'll not catch any serious shooter firing them from a smoothbore.

Rifling does more than just keep the projectile pointed in the right direction.

Ragnarok wrote:

jimmy101 wrote:the round may well be aerodynamically stable (and rifling isn't needed).

That's very debatable... it depends on your goal.

If you want to be able to fire rounds that will retain a good consistent ballistic coefficient and hit head on, rifling may not be necessary.

If your goal is accuracy and consistency of impacts, aerodynamic stability is far from enough. Most designs of airgun pellets are aerodynamically stable, but you'll not catch any serious shooter firing them from a smoothbore.

Rifling does more than just keep the projectile pointed in the right direction.

Actually, rifling does not keep the bullet pointed in the right direction, it keeps it pointed in the same direction (the direction of the barrel) which isn't the same as the bullets trajectory nor is it the "right" direction. A spun round has a non-constant Cd since the attack angle into the air stream changes as a function of distance from the barrel.

An aerodynamicly stable round (like a fletched arrow) always points (more or less) into the air stream and has a more consistent Cd during flight.

jimmy101 wrote:Actually, rifling does not keep the bullet pointed in the right direction, it keeps it pointed in the same direction (the direction of the barrel) which isn't the same as the bullets trajectory nor is it the "right" direction.

The difference between those is pretty insignificant for our purposes. Firearms at any range out up to maybe 1000 yards (for a moderately powerful rifle) will still have an angle of incidence with the target of less than a single degree.
If a round's nose is pointing less than a couple of degrees off it's course at 1000 yards, I think that's close enough that fussing over it is moot.

The effects of the change in Cd will have less effect on the impact point and velocity than the natural variations of the round.

hmm but that's true of firearms.. not of guns firing stuff at a high angle like mortars, artillery and spudguns

Wich is why their projectiles are often fin stabilised.
Wich keeps it facing airflow head on no matter what.

one way or another you don't have to use rifled barrels to achieve accuracy.. and at least now it's not really practical to build a spudgun with a rifled barrel...

sure it would be cool to increase sectional density of a round while still keeping it's Cd value low but in order to make it practical you have to first: calculate the right twist rate and get a decent quality barrel and then use consistent ammo.. idealy premade rounds (of course you can make your own ammo but it will be either time consuming or it won't have the same quality)

thre are other things in spudguns that need improving... most of them don't even have sights

could i rifle an alli pipe its only 7mm wide...

I dont think those tiny little grooves will impart much spin to a projectile, has anyone tried one of their rifled barrels yet? It would work much better if you carved a groove on the dowel that was helical shaped and used a something to index as it is pulled throught the barrel, also i would suggest making a wider rounded cutter as the line scrathcedby a nail/ scrrew etc just doesnt sound effective to me.

i guess the small riflings are betta than none

Copper can't be hardended like normal steel (heat treating) the best option is to use a cutting tool like you find on a lathe, id use a high carbon tool (its the best cutter you can get), it will cut throw nearly anything but the are $$$ a normal lathe bit could also work and is a lot less $$$

what would be better for the PVC or poly is to have a tool actually lathed out of a peice of cold steel as u could heat treat eh ends of the cutters so they will cut a lot easier, but that would take a lathe and a vertical milling machine

This topic has been dead for three years.No need to bump it like that..
epic.win101: Please stick to the recent topics.

Only revive an old topic if there is something significant to add.