Single pumping hybrid, "Strong Boy"

[hectmarr]

I am planning to build a low compression hybrid, about 3 or 4X, which uses manual force, using the bolt to compress the mixture. I have thought about using the firing gun, with a previously defined volume, to dose the butane. At the end of the day, it is a cylinder of known volume exactly the same as the one I am currently using to dose in my air pump hybrids.
After testing how much force I can exert through the bolt, using a fish scale up to 40 kg, and I generated 25 kg with a little effort, not terrible. The area of ​​the piston is 4.9 cm2, (2.5 cm in diameter), and with 20 kg I can achieve a pressure of 4 bar, enough to play for a while! The projectile's load, 1/4 "steel bb, is through the mouth of the barrel, and the seal is a screw-regulated o'ring (not seen in the drawing). It is a simple weapon and is only necessary the ammunition and a can of gas to introduce the fuel.
To load the butane, the tank must be pressed to flood the firing barrel with the bolt fully closed, and without placing the ammunition. Next, the bolt handle is retracted back to suck the gas into the combustion chamber at the same time as the air. Then the ammunition is introduced, and it is compressed with the crank, and then by twisting the bolt it is locked and ready to fire. I am seeing the real measures to build it.
It is already understood because it is called "Strong Boy" jajajajaja
 

[jackssmirkingrevenge]

I love the concept! The only thing I would change is reduce the diameter of the piston to allow a higher pressure to be reached with the same force applied to the bolt.

[hectmarr]

I am thinking about the amount of mixture that can be used. I made some numbers and the weapon would have a slightly strange shape, a fairly short barrel and a fairly long body.
You are right that by decreasing the area of ​​the piston the force can decrease for the same pressure, or with the same applied force, obtain more pressure. The problem is that if I decrease the diameter, to be able to load say 80 cm3 of mixture, the weapon must be longer, I mean the compression cylinder. My question is how much is the minimum amount of air - butane mixture, which can be used to achieve a decent shot ...
Of course, I'm not very interested in efficiency, it's just something different to shoot a little, and play.
The length of the firing pipe is conditioned by the amount of gas required in relation to the air, by stoichiometry, depending on the caliber. I can use 3/16 "or 1/4" balls.
I thought about the following.
Compression cylinder 2.5 cm in diameter, area, 4.9 cm2, useful length, (to compress), 16.5 cm.
It would have a mixing volume of approximately 80 cm3
The amount of gas at 5% would be 4cm3 of butane.
A 4.76 caliber barrel, steel bb, must be approximately 23 cm long, to be used as a dispenser.
It would look roughly as in the drawing
In another case, if I decrease the diameter of the piston to 1.8 cm, the area is 2.5 cm2. To obtain 80 cm3 of mixture, the useful length of the compression cylinder is 32cm. As double the length is necessary for the bolt system, the body of the weapon is 62 cm long and a 23 cm firing cannon. I have no problems with this appearance, I just have in mind that it is as comfortable as possible to zoom in.

[jackssmirkingrevenge]

I made some numbers and the weapon would have a slightly strange shape, a fairly short barrel and a fairly long body.

Look at rifle caliber bolt action pistols like the Nosler Model 48, they look pretty sweet.

[hectmarr]

Cute!!
Can you give me your opinion on the approximate minimum quantity of mixture that can be used, for a 4.76 mm caliber, a pipe length of 25 cm, in a 4X hybrid?
The approximate dimensions would be like this, (the measurements are in centimeters)

[jackssmirkingrevenge]

Have you tried modeling it on HGDT?

That's the best way to alter the parameters and see what gives the best power.

[hectmarr]

No ... I have no idea how to use that ... it's complicated for me.
If the caliber is 6.35 mm, the weapon would look more or less like this. The barrel has a length of 12.5 cm, to have, in that caliber, 4 cm3 of volume! I'm laughing alone here

[jackssmirkingrevenge]

No ... I have no idea how to use that ... it's complicated for me.

You're one of the smartest guys on the forum, surely it should not be too hard I'll be happy to answer any questions you might have if you try to use it.

Here is a model with the 0.25" barrel (because we like to make bigger holes )



I went with a 20cm long chamber 2.54cm in diameter, compressed to 5cm. The "ball release" is at 25 bar.

After that, I kept the same parameters but used a 1.9cm diameter chamber, still 20cm long but compressed to 2.5cm. "Ball release" is now at 50 bar.

As you can see, there is a significant increase in power, more than 50%, from using a smaller chamber at higher pressure:

[hectmarr]

okay. I will try to use the program that is very useful, no doubt. I am going to ask you the questions that I need, thanks for offering, and thanks for the simulation data, I am seeing them at this moment, to guide the design, to have measures to be able to build.

[jackssmirkingrevenge]

I am seeing them at this moment, to guide the design, to have measures to be able to build.

The basic conclusion is that much like for pneumatics, a smaller chamber at higher pressure is going to give more power.

[hectmarr]

Another way to do this is as in the drawing.
Locate the small butane tank outside, and use a piece of 6 mm plastic hose to dose the volume of butane, (technique that works very well). In this way, the barrel can be as long as desired.
On the other hand, I will use a rod that stretches to aspirate the butane and the air, but when compressing the mixture, and after locking in the notch, it protrudes little, precisely, at the time of aiming and firing the weapon, everything must be as comfortable as possible. To carry, in the same way, the rod is attached to the barrel and everything is much shorter.
In fact, this design does not provide anything of complexity, but it allows you to build a shorter and unlimited weapon in the barrel length, (which is going to be .25 caliber, because as Jack says, the bigger the hole, the better! )
Otherwise it will have 8X compression that is better, because of the simulation data it showed me. It will take about 25 kg of force, which I can exercise without problems, (yet!)

[Moonbogg]

This idea is awesome for sure. I had a similar idea for a larger cannon using an acme thread with a turning handle to compress the piston. The only thing I didn't like about the idea was the very long chamber, but with a smaller device like yours, it isn't an issue.
Perhaps you may consider incorporating a threaded end cap and a threaded rod with the piston head and a turning handle. I think you could get more compression that way, but the design gets a little more complicated because you have to seal the threads somehow. Even with just pushing the piston in like you have it should work well.
Regarding HGDT, it is very valuable for modeling the cannon and also measures the fueling for you. It's the best thing to happen to this hobby in my opinion. I'm convinced that both of my hybrids turned out as good as they did because of that program. It helps you optimize chamber to barrel ratios for the performance category you are looking for, among many other extremely awesome features.

[hectmarr]

This idea is awesome for sure. I had a similar idea for a larger cannon using an acme thread with a turning handle to compress the piston. The only thing I didn't like about the idea was the very long chamber, but with a smaller device like yours, it isn't an issue.
Perhaps you may consider incorporating a threaded end cap and a threaded rod with the piston head and a turning handle. I think you could get more compression that way, but the design gets a little more complicated because you have to seal the threads somehow. Even with just pushing the piston in like you have it should work well.
Regarding HGDT, it is very valuable for modeling the cannon and also measures the fueling for you. It's the best thing to happen to this hobby in my opinion. I'm convinced that both of my hybrids turned out as good as they did because of that program. It helps you optimize chamber to barrel ratios for the performance category you are looking for, among many other extremely awesome features.

Yes, you told me about that idea of you, of using the force of a screw to compress. It is a disadvantage to compress from a chamber at atmospheric pressure, because of the bulky chamber, especially in a large weapon. As you say, in a small weapon, this does not bother much. This is born of testing if an air pump that I have here was losing air, when I had to change the o'ring and I didn't have the force lever connected yet. To my surprise, applying force directly reached 6 bar, and I thought it could be used directly in this way. The facts gave me the corresponding lesson.
I like to use a threaded rod, I will try to do it. I am looking for 20 mm diameter steel tubes, which are recycled from car shock absorbers. Threads are not an option at the moment, because I don't have a lathe.
Do you know where to download HGDT? I will try to use this very useful tool.

[jackssmirkingrevenge]

You can download HGDT here.

I made a more "fair" comparison using the force you can generate with a single pump using different diameter tubes.

You said that you could generate 20kg of force, so with a 2cm diameter tube that's 6 bar.

If we go down to a 1cm tube, for the same 20kg force on the pump then we achieve 25 bar.

Here are the two situations simulated with a 12.5cm long barrel for 6.35mm steel balls, for each case the "burst disk" or in your case "o-ring release" is optimized to match the chamber pressure on ignition.



As you can see, even though the final chamber volume is much smaller (0.6cc vs 10.4cc) we get a more than 25% increase in power.

It is also interesting to compare barrel pressures for the two scenarios:



The smaller high pressure chamber has a higher peak barrel pressure but also a lower muzzle pressure, meaning that it should also have less noise.

[hectmarr]

Ok, the lesson you give me is very evident. Actually the force I can exert is more than 30 kg, without problems. I have given as normal value, 25 kg, for a little more comfort. I tell you that the CO2 gun that I have, needs 18 kg to be approached, because the hammer spring is compressed to the side of the barrel, and this force adds to that of inserting the pellet .22 into the barrel that is very tight ... Normally I make about 20 or 30 shots in a row and no problem.
I will try to get a compression tube as close to what gives the best performance according to HGDT, but the closest are motorcycle shock absorber tubes, which are made of 1 mm thick steel, and between 1.6 to 2 cm inside diameter. I will work with resin, the covers, and this is why I will not try to exceed the 8 or 9 bar of compression, which is what I have tried and I know that it holds up well.
I already have the two simulators on my pc. What is the difference between both programs? Just to know ...