projectile testing - any volunteers?

[jackssmirkingrevenge]

This thread raised some interesting questions regarding streamlined projectiles and it would be good to have some practical results to back up the theories

What I am proposing is that someone with a lathe, reasonably powerful pneumatic launcher capable of high subsonic muzzle velocities, and a distance over which to shoot. The projectiles illustrated should be manufactured, using a light tube (PVC, aluminium etc.) that fits closely in the barrel as the central body, with a heavy nose component (steel, lead etc.) and a lightweight tail component (foam, balsa wood etc.) in the following configurations:

1) identical nose and tail profiles
2) flat tail profile
3) elongated tail profile
4) "boat" tail profile
5) no tail cap

The test would have two principle objectives:

a) determining which shape is the most stable in flight, without the aid of fins or rifling

b) determining which shape allows superior velocity retention over distance

For the first objective, I propose that the projectiles are fired at large flat targets (such as sheets of thick cardboard) set out at various distances (say 5 or 10 metre increments out to 50 metres). A number of shots would have to be fired per shot type (projectile shape and distance) in order to determine an average patern. The targets should be examined for evidence of tumbling, which should be fairly obvious by the appearance of keyholing. This should also allow the degree of tumbling to be determined.

The projectile shapes found to be stable (exhibiting little or no tumbling out to 50 metres) are then selected for the second objective. Ideally a commercial chronograph is used to determine velocity after 50 metres of travel, but in practice it would be difficult to align the shot. Using the laptop/microphone method is probably the best option available to those without a professional testing range. For this test it would also be useful to fire a spherical projectile of similar weight to see what advantage if any is gained by using streamlined projectiles.

I realise that the different amounts of tail material would alter sectional density and therefore change a parameter beyond simple aerodynamic shape, however in practice this should be negligble in terms of results.

It would be great if someone could take the trouble and do a reasonably rigorous test like this one. Why don't you do it yourself, I hear you say - the answer is simply space, I don't have enough room to shoot over that will give me meaningful results. I am however willing to make a pengun/markergun or similar as an incentive of sorts to anyone willing to conduct this expertiment.

Any takers, or comments as to what other parameters ought to be tested?

[Technician1002]

For a proper shape comparison, all projectiles should be weighted so the weight is identical even with various tails. A light one missing a tail will have an initial launch velocity advantage.

[jackssmirkingrevenge]

Fair point, but as what is varying is what I envisage to be lightweight material that represents a small percentage of the total weight, I don't expect the difference to be significant. Still, if accurate weighting is possible it would be even better. I tried to simplify the parameters in order to make the test more accessible.

One could also say that shape 5) is at a disadvantage because it has greater dead space.

[Technician1002]

After finding I can pressurize empty pop cans during launch, shape 5 may use the dead space for propellant space.

[Labtecpower]

If I have some spare time, I will turn a nose cone on the lathe.
Maybe I can do some testing this weekend (no promises )

[ramses]

I'd be game for it, depending on how busy I am this summer. I have lead and PVC tube, but no suitable launcher at the moment. I suppose I could use my piston hybrid as a pneumatic.

[Labtecpower]

of course, this is just about range. if I had a hybrid, I would have used it

[jackssmirkingrevenge]

Thanks for the feedback so far, I look forward to your results and stand by my offer to reward the most complete effort with one of my small pneumatic creations

I'd also like to take the opportunity to dig up this proposal - I think this forum has stagnated somewhat of late and needs those with the time and resources to do some relatively rigorous scientific testing - especially for the adolescents amongst you who would like a career in science, it's this sort of experimental attitude that will get you places in life

[jakethebeast]

Well, if nobody wants to try this, im going to get a lathe in summer and build a high flow hammer valve pcp airgun so if no-one has tried this untill that i might giv it a try (if somebody has tried this, i shall try it myself )

BTW i hav about few square kilometers forest and field surrounding my home

[ramses]

of course, this is just about range. if I had a hybrid, I would have used it

you loose out on consistency, though. Especially if your fuel meter sucks like mine.

Also, my property is only around 100 feet long. I'd be going *em* elsewhere to do these tests, and I would prefer to keep noise levels down.

[jackssmirkingrevenge]

You lose out on consistency though, especially if your fuel meter sucks like mine.

This is one of the reasons I suggested a high performance pneumatic as a test launcher. It's also less likely to set the tail section on fire

[irisher]

Would a 1.25" barrel shooting 1" pvc rounds work for you or were you thinking larger bore?

[Technician1002]

Setting the tail section on fire would be against the rules.. No flaming projectiles allowed.

[saefroch]

I'd offer my assistance in testing, since I think I might actually be able to find these projectiles, but I can think of no good way to find a projectile .364" in diameter a ways away. AP exams are approaching, and afterwards I'll have more free time to do testing like this.

I also need to buy myself a gauge, but that hasn't stopped me yet!

[jackssmirkingrevenge]

Would a 1.25" barrel shooting 1" pvc rounds work for you or were you thinking larger bore?

I was thinking 3/4" - 1/2" bore actually, so there would be less material cost in making the projectiles - but bigger would be better as the effects could be more easily observed

No flaming projectiles allowed

This must be what I sound like