Check this out!

[jackssmirkingrevenge]

Joerg measured 50 fpe.

... using fairly massive projectiles, so it's not really a fair comparison. A baseball thrown at 100 feet per second (and they usually fly faster) carries 50 ft/lbs of energy.

Can any springer deliver 50 fpe?

You'd have to see what it gets with a pellet to be able to compare. I'm sure a springer could deliver well in excess of 50 ft/lbs if it fired its piston as a projectile

Can you shoot your springer as well as this guy?

Don't be silly, while that's skilful with a slingshot anyone could shoot a springer better than that, could he hit something reliably more than 10 yards away?

[Ragnarok]

Joerg measured 50 fpe.
Can any springer deliver 50 fpe?

If we're going down this route, springers can exceed 1200 fps. Can any slingshot deliver 1200 fps?

What you'll find with slingshots is that their efficiency comes down as draw strength goes up. A 300 pound slingshot isn't going to record 6 times the energy of a 50 pound slingshot.

The recoil from the snapping rubber will affect the accuracy.

As does a springer's recoil, but springers recoil BEFORE they shoot. There are still people out there who can use them to put down 10 shot groups that go through the same hole at 30 yards.

Can you shoot your springer as well as this guy?

If you want fair comparisons, putting me (good, but not perfect) against the best slingshot shooter you can find on Youtube... it seems a bit lopsided, at first glance.
I'm nowhere near the best, nor am I a trick shooter. My springer is a target rifle - and at 10 lbs and a little over three feet long, it's not exactly cut out for shooting coins out of the air.

However, anything where he wasn't throwing things up in the air, I could easily replicate with my springer...

... from 5 times further away.

[boyntonstu]

Homemade Pneumatic Cannon discussion..

Can rubber supply psi?

[jackssmirkingrevenge]

Can rubber supply psi?

Of course, psi is a measure of pressure which is force divided by area, rubber when stretched provides a force over a certain area

[boyntonstu]

Joerg measured 50 fpe.
Can any springer deliver 50 fpe?

If we're going down this route, springers can exceed 1200 fps. Can any slingshot deliver 1200 fps?

What you'll find with slingshots is that their efficiency comes down as draw strength goes up. A 300 pound slingshot isn't going to record 6 times the energy of a 50 pound slingshot.

The recoil from the snapping rubber will affect the accuracy.

As does a springer's recoil, but springers recoil BEFORE they shoot. There are still people out there who can use them to put down 10 shot groups that go through the same hole at 30 yards.

Can you shoot your springer as well as this guy?

If you want fair comparisons, putting me (good, but not perfect) against the best slingshot shooter you can find on Youtube... it seems a bit lopsided, at first glance.
I'm nowhere near the best, nor am I a trick shooter. My springer is a target rifle - and at 10 lbs and a little over three feet long, it's not exactly cut out for shooting coins out of the air.

However, anything where he wasn't throwing things up in the air, I could easily replicate with my springer...

... from 5 times further away.

Let's discuss a few of your points:


This is a homemade pneumatic forum, what does a store bought springer have to do with anything here?

A rifled barrel target rifle against a home built copper cannon?

"A 300 pound slingshot isn't going to record 6 times the energy of a 50 pound slingshot."

On what evidence/theory do you base this statement?

Would 6 individual slingshots deliver 6 times the energy?

"If we're going down this route, springers can exceed 1200 fps. Can any slingshot deliver 1200 fps?"

Interesting question:

AFAIK No crossbow or compound bow has ever gone over 350 fps.

"Team RealTree® HD 175 Crossbow (175 pound draw)

Endorsed by Realtree® as on of the Best Crossbows on the market, the Team Realtree HD 175 is a dependable, rugged, accurate hunting tool with speed up to 305 fps.

However a compound bow powering a pump has doubled that to 600 fps.

Joerg's slingshot delivered 426 fps on his first try using the airowgun.

If you use the rubber speed itself, you will never get there.

Why is 1,200 fps so important?

A .380 auto goes 950 fps.

A .45 auto goes 950 fps.

I'll take a hit in my shoulder from any .22 1,200 fps springer before choosing a hit from a .45 auto.

How about choosing a a golf ball at 500 fps?

OTOH It may be possible with 300 pounds of compressor force to achieve 1,200 fps with a 14 gr pellet.

BoyntonStu

[inonickname]

A rifled barrel target rifle against a home built copper cannon?

With my homemade aluminum (well, it's the same size as a copper one) I can put consistent ammunition through the same hole from a much further distance, which I doubt a slingshot could get held on a shooting bench. And I'm willing to say a commercial rifle could have better accuracy, so there's no comparison.

You think multiplying the number of cords will multiply the power? No. It will increase it, but not multiply it. Take the airforce condor, basically the most powerful .22 PCP you can buy, which when modified has comparable power, accuracy, velocity and range to a .22LR. (and respectable out of the box) It shoots on 3000 psi air/N2.. do you think doubling the pressure with the same ammunition would double muzzle energy? No, not at all. You reach a ceiling where any benefit gained is nearly non-existant.

However, with more push/force you could push a heavier projectile to similar velocities; i.e. much more muzzle energy.

I'll also guess that using a piston is less efficient at transferring energy to heavier projectiles, though compression heating will carry benefits for lighter projectiles.

[boyntonstu]

A rifled barrel target rifle against a home built copper cannon?

With my homemade aluminum (well, it's the same size as a copper one) I can put consistent ammunition through the same hole from a much further distance, which I doubt a slingshot could get held on a shooting bench. And I'm willing to say a commercial rifle could have better accuracy, so there's no comparison.

You think multiplying the number of cords will multiply the power? No. It will increase it, but not multiply it. Take the airforce condor, basically the most powerful .22 PCP you can buy, which when modified has comparable power, accuracy, velocity and range to a .22LR. (and respectable out of the box) It shoots on 3000 psi air/N2.. do you think doubling the pressure with the same ammunition would double muzzle energy? No, not at all. You reach a ceiling where any benefit gained is nearly non-existant.

However, with more push/force you could push a heavier projectile to similar velocities; i.e. much more muzzle energy.

I'll also guess that using a piston is less efficient at transferring energy to heavier projectiles, though compression heating will carry benefits for lighter projectiles.

There is room for doubt on increased force/pressure by adding bands.

However as a slingshot propelling a stone, more bands will project a heavier projectile at the same speed for proportionally increased energy.


"which I doubt a slingshot could get held on a shooting bench. "

I do not understand this.

I am NOT proposing a slingshot airowgun.

I am proposing a full stock 'spear gun' type rifle with good sights and a good trigger.

I am fairly certain that it would do as well as your aluminum barreled gun in a side by side test.

Is a crossbow as accurate as your homemade gun?

Think crossbow and please forget slingshot.

BoyntonStu

[Brian the brain]

I've shot marbles halfway into wood using the power of good old rubber bands...

Wich would put a lot of the pneumatic marbleguns on this site out of the contest..

Why not skip the pneumatic part and use them directly?

Less noise...


Less hassle.

[boyntonstu]

I've shot marbles halfway into wood using the power of good old rubber bands...

Wich would put a lot of the pneumatic marbleguns on this site out of the contest..

Why not skip the pneumatic part and use them directly?

Less noise...


Less hassle.

BTB,

A slingshot will launch as fast as the rubber travels.

The airowgun doubles the speed to 600 fps and it is my goal to reach 1,000 fps with more rubber power.

I want noise! I want to hear an see a blast of de-compressed air.

Did you see the video?

No slingshot would ever yield such a sight.

BTW I designed a very simple trigger mechanism today.


BoyntonStu

[boyntonstu]

I purchased a 0-50 pound fish scale today.

When I pull the rubber 300% it measures 35 pounds.


300% is the factory specification although Joerg recommends 350%.

I like multiples of 50 as a nice even number.

Should I pull it to 50 or settle on 35 for rubber life?

Another factor is draw length.

If the rubber is relaxed back at its 10" starting position, after retracting 20", it is wasteful to have the cylinder longer than 20". Correct?

The next factor is load. If the air compression load does not slow the piston, adding addition rubbers is also wasteful.

The ideal, is to match the diameter to the rubber.

Perhaps using a larger chamber is the correct path.

Also, the more I think about it, the more I convince myself that a restriction in size from chamber to barrel is necessary for the air to compress.

That is how the Airowgun is designed, a large chamber, a small return line, and then the barrel.

Suggestions?

BoyntonStu

[Ragnarok]

This is a homemade pneumatic forum, what does a store bought springer have to do with anything here?

You should always ask: Is the way I'm doing this an effective option?

What you're looking at is more complication, more risk and likely more cost than a conventional springer.

When I say more risk, let me explain. I crushed off part of the side of one of my fingers trying to do this kind of thing. It was pure blind luck that stopped me doing any worse.
This was in spite of precautions I was taking to avoid such things. In the end, even for an almost abnormally quick healer like me, it took months to recover and leaked all kinds of fluids I didn't even know the human body could produce for most of that time.
And I did that with a whole lot less power than you're trying to use.

Ask yourself if those are risks you're prepared to take.
Based on what I've seen of your posts on the forum, I'm really not sure you're fully aware of all the hazards that can exist with a project like this, nor how to spot and avoid them.

I'd advise starting with a less ambitious project, then come back to this when you're ready for it. I know, you wander in, see all these shiny projects and want to follow suit, but I started spudding years ago, and I've still got to double back to my ambitious early projects.

"A 300 pound slingshot isn't going to record 6 times the energy of a 50 pound slingshot."
On what evidence/theory do you base this statement?

A greater proportion of the total energy is absorbed as heat and kinetic energy in the elastic as draw strength and velocity increase.

It's just like if I pressurize my cannons to twice the pressure, I don't get back twice the kinetic energy.

Why is 1,200 fps so important?

The specific number isn't important. But I'm illustrating there are areas in which either form of power can best the other.

While slingshots might have a slight edge on energy, springers can wipe the floor with them on velocity and accuracy.

What I'm trying to say is that it's fairly pointless throwing up "Can ANY X do Y?" challenges, because it's easily parried and countered.

[jeepkahn]

i just take a 1.5" length of wooden dowel, Drilla .5" deep by .375" hole into the center of it, then take 18" of 1/4" pipe wrap and slide onto a nockless arrow, insert the base of the arrow into the wooden sabot, insert into decimater, and launch at over 1000fps.... Thats an arrowgun!!!

[jackssmirkingrevenge]

Thats an arrowgun!!!

showoff

[THUNDERLORD]

...Should I pull it to 50 or settle on 35 for rubber life?...

My suggestion, go for power (like Jeorg suggested)...that way you'd sell more replacement bands.

...The next factor is load. If the air compression load does not slow the piston, adding addition rubbers is also wasteful....

I don't see how more bands is wasteful?
For example, you probably won't ever be able to get 3000 psi very easily.
Besides, with more bands a larger shorter piston could be compressed to higher pressure/volume.

...Perhaps using a larger chamber is the correct path....

Like was suggested before, IMO a (much) larger diameter with the rubber band at nearly 2/3rds maximum when at rest.

...Also, the more I think about it, the more I convince myself that a restriction in size from chamber to barrel is necessary for the air to compress....

I suggest you check out the PVC pneumatic pogo stick threads (no time to find link ) to get an idea how much force/ volume is needed to generate that volume air at still low pressure (for high velocity app.).
Seems like a large diameter larger volume cylinder with much shorter stroke (since it will build and exhaust faster) would be best best...as was also suggested before.

...That is how the Airowgun is designed, a large chamber, a small return line, and then the barrel....

The "return line" has been referred to as a "convoluted transfer tube" in the past here IIRC.
IMO the cylinder is waaayy too long (understandably so it will act similarly to a normal arrow pull).
Unnecessary and not fully optimized IMO.

...Suggestions?

BoyntonStu

Well, you asked for them.
BTW, I don't understand all the debate about "springers" Vs. your concept idea, since it is a "springer" concept with a different spring (rubber band/tubing instead metal coil)...
Still daydreaming of combustion pressure against piston rather than metal coil spring pressure myself. (A combustion springer(?)) 8)

Thats an arrowgun!!!

showoff

(edit):although that version sounds impressive,
Try a plastic foam wadding and break-away sabot up front and 30+ arrows at similar velocity...
Or invert the idea and use pressure (from IDK, Propane, to cock the bowstring with a magazine fed crossbow...would be : 8) xD!!!
Gotta rest few and get back to work again...noticed I'm getting cut lately...TMI but heavy work builds a good shooting platform. 8)

[inonickname]

Is a crossbow as accurate as your homemade gun?

Think crossbow and please forget slingshot.

BoyntonStu

Has anyone noticed how one sided and perfect he is? Like the HHO rubbish he came up with.

I'd say the accuracy is very comparable, however seen as my gun would have both MORE velocity and MORE muzzle energy there will be less projectile drop over range (ignoring whatever projectile factors).

Yes, with a sear, trigger and stock you will potentially have more accuracy than a slingshot. However, you will have similar recoil issues to springers, except on a much larger scale.

If you do build this, feel free to come over here and compare.

I have no doubts that potential is definitely there, but it's not going to be record setting.