SpudFiles

Hey!

Recently, I started a competition with a friend of mine to see who can build the most accurate airgun. We will be firing at targets from 10 to 50 meters (with 10 meter intervals) to see who can get the best accuracy and/or grouping. We agreed on three regulations: Sub-15mm caliber, no CO2 and has to be a portable design. The plan is, obviously, to completely obliterate him.


The question

What kind of ammo should I use to get the best results?

Here's a list of properties I'm looking for:
- Can reach out to 50 meters, while being driven by a spring and piston*
- Ballistics that can be predicted reliably** (no matter how complicated)
- Manufacturable from parts/materials that can be bought or easily molded
- Will be fired out of a barrel without rifling
- Preferably drag-stabilized rather than fin-stabilized
- Preferably 6.0 or 8.0 mm caliber, but up to 15.0 mm
- Preferably able to pierce a piece of paper at 50 meters


Some more information

Both of us will likely use a spring mechanism* which will drive a piston. Alternatively, I also thought of using rubber bands in combination with some sort of pulley system to drive a plunger through a piston.

I currently have .12 and .20 gram BB's*** (6 mm). I know that the .20 ones could possibly reach out to 50 meters without much trouble, but being light and spherical, they will also be hard to predict. Saboted BB's could be used to prevent any kind of spinning.

And finally, I'm extremely intrigued by drag-stabilized projectiles. I could cast the tip out of whatever and stick something like a foam or paper cilinder on the back. This will allow me to make heavier projectiles for the same caliber (but increases parasitic drag).

If you genuinely do believe that there is absolutely no possibility that any of the requirements can be met with a spring-propulsion system, you could also recommend me an ammo-type that can be used with compressed air (preferably under 8 bars of pressure).

Thank you for reading and I hope you guys have some good recommendations for me!

Notes

* Please don't try to discourage us about this.
** Some examples of external effects I could compensate for with calculations: Gravity, wind resistance, windage, altitude, temperature, humidity, magnus effect, parasitic drag (for non-spherical projectiles) and coriolis drift (probably negligible).
*** BB's are not sold in my country, so just assume these are my only options.

0.20g bb won´t work, go get some 0.35g or 0.40g bbs, they are for airsoft sniper rifles. I was able to reach a 3/4 grouping at 50m with 0.25g bbs with a homemade airgun, but needed to be one a windless day and I used more than 8bar. Good airsoft bbs are far better than homemade drag-stabilized projectiles, you better stick with factory made ammos. If you are going to use a spring+piston, I won´t help you about your gun at all. If you go for a airgun, I think I have some design that may be suitable for you.

The simplest approach is to use a 3/4 inch QEV with a fin stabilized projectile that has pusher plate style sabot for a 3/4 inch barrel.

A long barrel with a good sighting system will help considerably.

Tsukiten wrote:If you genuinely do believe that there is absolutely no possibility that any of the requirements can be met with a spring-propulsion system, you could also recommend me an ammo-type that can be used with compressed air (preferably under 8 bars of pressure).

I've always said it on this forum and will say it again, springers are great because they're self contained but unless you have a machine shop to make one, don't even consider it. Also, if your aim (see what I did there ) is accuracy, then the vibration associated with a spring piston rifle is a distinct disadvantage - a springer is much more difficult to shoot accurately than a pneumatic.

Also, power is an issue. A launcher capable of hitting a target at 50 metres has to be quite powerful, and if it was a springer it would need substantial construction, certainly not something you're going to achieve with rubber bands.

A simple QEV pneumatic is much easier to build and will be much more powerful, even if you're limited to 8 bar.

I currently have .12 and .20 gram BB's*** (6 mm). I know that the .20 ones could possibly reach out to 50 meters without much trouble, but being light and spherical, they will also be hard to predict. Saboted BB's could be used to prevent any kind of spinning.

BBs are a terrible ammunition for shooting at distance. A sphere is a poor ballistic shape, and due to the light weight the sectional density is also pretty bad.

It sounds like the best solution in the context of your available tools would be to use a consistent metal part (such as a ball bearing or bolt) in a section of barrel material, then pour epoxy or similar casting material et voila, nose heavy drag stabilised projectile with a good ballistic shape.

Jack, bbs aren´t that bad, don´t know what kind of bbs you used, but if you buy these expensive ones, they are very stable at 50m. Of course they won´t fly as much as a pellet, but bbs are better when used in a smooth bore, and has a better ballistic than a bolt. Without a drill press it´s very hard to sand down the bolt to a smooth shape too.

A cylinder with a rounded head has a lower drag coefficient than a sphere.

You can always use a carriage bolt

I would still go for the 6mm bb, 50m isn´t far at all, launching a 0.40g bb requires a much cheaper and safer launcher than a heave metal head bullet.

wyz2285 wrote:I would still go for the 6mm bb, 50m isn´t far at all, launching a 0.40g bb requires a much cheaper and safer launcher than a heave metal head bullet.

At least then get lead or steel balls...

[size=150]wyz2285[/size] wrote:0.20g bb won´t work, go get some 0.35g or 0.40g bbs, they are for airsoft sniper rifles. I was able to reach a 3/4 grouping at 50m with 0.25g bbs with a homemade airgun, but needed to be one a windless day and I used more than 8bar. Good airsoft bbs are far better than homemade drag-stabilized projectiles, you better stick with factory made ammos. If you are going to use a spring+piston, I won´t help you about your gun at all. If you go for a airgun, I think I have some design that may be suitable for you.

If you read the bit under "Notes", you can see BB's are not sold in my country. The .12 and .20 ones I have have come all the way from USA. Either I run with those, or I modify them. Candlewax has a slightly lower density than the .20 gram BB's. If I would mold and stick an extension to a BB out of candlewax, it effectively makes it heavier while maintaining the same diameter and still keeping the center of mass in a favorable position.

But thanks for your input, all information is valuable!

[size=150]jackssmirkingrevenge[/size] wrote:
I've always said it on this forum and will say it again, springers are great because they're self contained but unless you have a machine shop to make one, don't even consider it. Also, if your aim (see what I did there ) is accuracy, then the vibration associated with a spring piston rifle is a distinct disadvantage - a springer is much more difficult to shoot accurately than a pneumatic.

Also, power is an issue. A launcher capable of hitting a target at 50 metres has to be quite powerful, and if it was a springer it would need substantial construction, certainly not something you're going to achieve with rubber bands.

A simple QEV pneumatic is much easier to build and will be much more powerful, even if you're limited to 8 bar.

BBs are a terrible ammunition for shooting at distance. A sphere is a poor ballistic shape, and due to the light weight the sectional density is also pretty bad.

It sounds like the best solution in the context of your available tools would be to use a consistent metal part (such as a ball bearing or bolt) in a section of barrel material, then pour epoxy or similar casting material et voila, nose heavy drag stabilised projectile with a good ballistic shape.

What matters to me is that the projectile doesn't come to a dead stop (zero horizontal velocity) before reaching 50 meters. If the projectile would impact the target at an 45-degree angle, that really is good enough for me. As long as there's a chance that the numbers produced by equations and there real-world results match up a bit.
About power: currently I'm trying to measure the spring rate of the spring I have, after which I can calculate what its maximum performance would roughly be like. If that doesn't look very optimistic, I can go pneumatic or try out that crazy idea of mine with rubber bands.

Note that the rubber bands will not directly drive the piston. The rubber bands could for example drive something along 5 times the length of the piston, after which a system of pulleys or gears or whatever transforms the length of displacement into the length of the piston and thus multiplying the excerted force on the piston by 5.

I uhh...hope that was not too confusing...bit hard to explain in words.

[size=150]wyz2285[/size] wrote:
I would still go for the 6mm bb, 50m isn´t far at all, launching a 0.40g bb requires a much cheaper and safer launcher than a heave metal head bullet.

Yeah that's what I was thinking.



I'll do some measurements and calculations and see if I can cross out some possibilities. But secretly, I'm hoping to prove everyone wrong (:

BB's are not sold in my country.

Witch country do you come from???

wyz2285 wrote:

BB's are not sold in my country.

Witch country do you come from???

yaaay.

tsukiten wrote:pic

which part of the country?

BBs are sold there, I´m pretty sure. You just didn´t look hard enough or you looked at the wrong place

BBs are sold there, I´m pretty sure. You just didn´t look hard enough or you looked at the wrong place

nope, nowhere to be found

You can import them from germany tough, they aren't restricted AFAIK

Labtecpower wrote:which part of the country?

Uit Amsterdam, aangenaamd. : P