SpudFiles

I tested using steel drill bits as projectiles out of my smoothbore .177 coaxial gun, and the grooves in the bit acted as rifling and enabled the bit to fly straight and penetrate deeply without fins. I don't have the means to test this out from far away, or at stronger targets such as steel sheets so if anyone wants to try it.(JSR? )


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sagthegreat wrote: I don't have the means to test this out from far away...

What was the approximate range...muzzle to target, and how reproducible were the results?

at 10 feet away, 9/10 of them self stabilized
at 20 feet away, 7/10 of them self stabilized
at 30 feet away, 5/10 of them self stabilized

What i wanted to test was like 50-100 feet away

It doesn't sound like it's self-stabilising then, at least not efficiently enough to be worth the high cost of drill bits.
I wouldn't be surprised to have similar proportions of unstabilised projectiles not yet tumbling at those distances.

If they appear stable, I would wager it is more to do with the nose heaviness than the projectiles spinning, air rifling doesn't really work.

at 10 feet away, 9/10 of them self stabilized
at 20 feet away, 7/10 of them self stabilized
at 30 feet away, 5/10 of them self stabilized

If it worked, 10/10 should hit head first at 30 feet.

It's cheaper and more effective to thread a bolt into a length of tube.

jackssmirkingrevenge wrote:air rifling doesn't really work

Well, it's worth saying that you'll sometimes find projectiles with angled fins in order to induce spin (the first example to mind is the RPG-7), but it's not for stability.

It makes any imbalance in the drag of the projectile average out in all directions, causing it to take a slightly helical trajectory rather than a hooking one.

jackssmirkingrevenge wrote:If they appear stable, I would wager it is more to do with the nose heaviness

The thing is, I load then with the "drill" end first, which is lighter due to material being taken out to form the drill pattern, and they all hit with that side going into the target



I tried from 25 feet vs a steel lid and they perform great! Compared to just shooting a steel rod, a drill bit has a way better chance of self stabalizing

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I have to try this...

edit: I was unable to replicate your results at 15 feet, here's 5 shots fired head first at a cardboard box:
I tried different bits and got the same results, even when firing them tail first - none of them flew straight.

I would surmise that you're not seeing the tumbling because of the high velocity and short distance.

Have a look at this unstabilised unrotated projectile fired at supersonic speed:

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It starts to tumble immediately, but for the first instants of its trajectory it is still travelling more or less straight enough to make a round hole in a target.

that video pretty much summarizes it then...

just out of curiosity, what type of cannon did you use, and what material did you use for wadding?
I used my coaxial with 12 inch barrel and 200psi, with a pellet as a backing

I used this at 400 psi with an airsoft BB as a sabot.