Home made PCP airgun

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"SPC-Racing"You wanted some comments, well here they are.

Have you calculated the hoop stress on the pressurized parts and selected the material used accordingly? How about fatigue factors? Or factors of safety? And what about the polymer creep issues mention earlier? What about potential stress risers? Did you recognize and allow for them in the design? If there were a failure, are the materials involved selected and designed to minimize user exposure and risk during a possible failure?



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I suppose I didn't design the gun to last. It's not designed to store pressure for long, as it's single shot. For that reason I didn't think I needed to consider plastic fatigue. I usually just wear gloves, a jack and a paintball mask and hope for the best. I just took pipe that I saw other people use without failure, time and time again, looked at the psi rating at 73 degrees F, decided to keep a maximum of 200 psi below the max working pressure, and take into consideration that cold or hot weather changes the working pressure of the plastic, and use accordingly. Then I put it into a design, cut a 2x4 into the shape of a stock, fit some metal parts around it, came up with a valve spring release, added a Schrader valve rated for 800 psi, and thought it seems simple enough. It's not quality. It's just fun.................simple fun.

Please watch this short video.
Would that really kill someone?
 
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Don't discount any of the safety concerns here whatsoever. You are absolutely playing with lethal energy levels. A danger that you're well acquainted with and I suspect that you have way more experience with it "the danger" than most people ever will.
The one and only definitive value in any calculated guess is failure. There is no other standard. You absolutely must learn and understand the failure point in order to make innovative progress. The only way to do this is to build your product and test it beyond its failure point. Then you've learned something useful in the development process.

One thing that can't possibly be taught in school is intelligence. It's a natural attribute. Anyone that is half way good at being a student can buy an engineering degree. It doesn't make them any more intelligent than they were before they started. It certainly doesn't make them capable of engineering. Not as it relates to ingenuity. You are privileged to have this natural tallent.
 
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"1kshooter"how do we stop this troll ...and if he is not a troll the few not so bright people that are egging him on are actually liable for doing so if he does get hurt ....I think a Mod needs to step in and kill this post! 
just my .2
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Definitely a troll. I really am surprised a mod hasnt done anything yet. I agree a mod needs to end this.
 
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"LDP"
"1kshooter"how do we stop this troll ...and if he is not a troll the few not so bright people that are egging him on are actually liable for doing so if he does get hurt ....I think a Mod needs to step in and kill this post! 
just my .2
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Definitely a troll. I really am surprised a mod hasnt done anything yet. I agree a mod needs to end this.
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I am not a troll. A troll wants trouble. I came here and asked questions about my gun. I provided pictures of my gun. I have been respectful. Trolls try to cause trouble. Please stop the accusing. Sure aren't friendly.
You can't expect someone who's been building and playing with PVC airguns to be immediately acceptant of the idea of stopping a hobby, within 2 days after some people told him it's dangerous. I'm not stubborn I'm just not sure I see the danger and I don't want to give up a hobby of mine just because I joined a forum, asked questions, and people rebuked me.
 
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Just because other people do it, or have done it, doesn't mean that it's a good idea. Judging from that video, if the PVC pipe were to explode while the gun is next to your head, you risk lacerations, embolism, foreign objects in the eye...is it going to kill you with blunt force trauma? Probably not. But I don't want to risk a cut in the jugular vein in your neck right next to where you're holding the gun. 

A steel pipe would be safer, but that's still far from safe. The pressure vessels on PCPs are either carbon fiber wrapped bottles, or machined metal. Definitely not extruded PVC or steel pipe where all the molecules or grains are arranged longitudinally down the length of the pipe. 

Go get a job at McDonalds. Quit after a month and buy yourself a gun.
 
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But why do people think I'm a troll. Tell a guy who loves motorcycles that they're dangerous and he should stop. Then see what he says. He's probably not going to feel compelled to stop after two days of being told that. And if you told him he was trolling you for not stopping, and instead putting up an argument, any onlooker would think that your being ridiculous.

@ztirffritzYes, I may eventually give up my gun. But not because people were mean, told me I was a troll, or called me stupid. Your forum certainly doesn't help people grow in the hobby. Rather attack newcomers. That's my experience this past day.

Also, PCP's hold several thousand psi, not a measly 150-230 psi. Standard steel pipe at home depot has a rated working pressure of 600 psi, and hydraulic tubing from my local hardware store, Skenks hardware has a working pressure of 3456 psi, and a burst pressure of like 18000 psi. Any of those would work.
 
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Guys I think we have done everything we can to try and let this member know just how dangerous this field is that he is playing with. Like my grandmother always told me, there are none as blind as them that can not see! If he can not see now from the responses from people with a lot of knowledge in this field that he is playing with a ticking time bomb, then there is not much else we can say. This is only going to end badly and due partly to his fathers lack of supervision, knowing what his son is doing and not intervening. I hope he continues to use his mind creatively, but in a totally different field, Neil.

PS. your analogies to driving cars and riding motorcycles just shows how immature you are and how little you understand about what is being said on here and why. Maybe you should direct your anger at your father for not caring what you do and not at the caring people on here who are trying to give you some sound advice, which you seem determined to ignore. You need to grow up and act more responsibly and listen to people with a lot more experience of life than you have. 

By the way you talk about using low air pressure that is not that dangerous, I had a friend who decided to ignore the advice we gave him and tried to weld the rim on his truck with the tire still inflated, only about 50psi so what was the danger. The rim exploded and he was killed in a very nasty way, not that there is ever a good way, but the way he died was very painful and ugly. Had he listened to the sound advice he was given he would still be with us today, please think about what you are doing before going any further. 
 
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You still do not get it, you do not have a good understanding of the field you are messing with, the point I was trying to make was that had he listened to people with more experience than he had, he would still be alive today. You have a lot to learn before taking your designs any further, I urge you to do some very good research and learn a lot more than you know now before taking this any further. No we are not teenagers, most people on air gun sites are adults with a lot of experience with air guns, you should listen to those with experience instead of taking it to heart and thinking they are being mean, they are all trying to protect you from the inexperience of youth, Neil.
 
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Would you tell that to the people who made the Girandoni air rifle? The pressure vessel was made of cast iron pressurized to 800 psi with 1500 strokes of a bicycle style pump mechanism? Was that not of the same danger. Someone on the forum showed me a chart of pvc pipe pressure rating. The schedule 40 3/4 inch pipe I'm using has a burst pressure of 1500 psi and working pressure of about 300 psi. Schedule 80 has a burst pressure of nearly 2000 psi. Strength increases as temperature increases according to Charlotte pipe company, but impact strength is less.



However according that same site, the pipe only retains 20% it's strength at 120 degrees F. And 140 degrees F is the maximum operating temperature.
 
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You are still arguing about something you do not understand, never mind things that were made in the past, what you have made is potentially very dangerous to you and anyone close by to you when you use it. Instead of trying to justify what you are doing by adding articles related to something that was much better engineered than yours try listening to the sensible advice you have been given by people with a lot more experience and Knowledge than you have. I am done trying to talk any kind of sense into you, you obviously know all there is too know about this subject so there is not much any of us can do to help you, You said you came here for help, you have been given it, if you decide to ignore it then there is no point in asking for it.I hope this thread does get deleted because it does not reflect well on those of us who take this hobby seriously, Neil.
 
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Maybe your health does not matter to you but it matters to the rest of the air gun community. None of us want to see a youngster get seriously injured because of his lack of experience in a very dangerous area. This is an adult forum and when adults see someone asking for help, they will give it, no matter if it is not the help asked for, if it has do do with safety, advice will always be given freely by the more experienced air gunners because we all want to expand the numbers of people in our community and want them to all be safe. I have come across this type of reaction before and it also came from teens, instead of seeing advice about safety it gets seen as criticism, when you are older and have more experience of life you might see the advice in the spirit it was intended, to keep you safe! I see I am wasting my time trying to help you so i will just wish you good luck and hope you stay safe, Neil.
 
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"usabro"
Tell me what you think, and if it has the same or more power as a .22 LR.
Let me know your thoughts and upgrades!

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usabro

You asked the members of this forum what we thought. And several shooters, builders, engineers, and tuners provided their thoughts. They also answered your question about the relative power of your projectile, and gave you a few ways to calculate your FPE.

It sounds like some people are recommending that you stop using the PVC air tube and upgrade to something that is more robust, and has been certified and tested well beyond your operating pressures. However that is only 1 piece to this complicated and dangerous puzzle, which will lead to many more questions regarding the safety and integrity of the other components.

If you have your heart set on building from scratch you will have to do a lot more research, and ask a lot of questions.

Another alternative would be to save up your pennies and purchase an entry level PCP (some of which can be had for under $200), which you can take apart and tinker with till the cows come home.

If you ask more specific questions you will get more specific answers. If you want peoples thoughts & opinions you will get just that. 
 
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The biggest problem I see is that people, including the original poster, keep thinking that PSI pressurized liquid is the same as PSI pressurized gas. If I build a theoretical infinitely strong pressure vessel that has a piston at the top of the vessel and fill the vessel with liquid I can't really compress the contents much at all, yet the pressure in the vessel will rapidly spike to many thousands of PSI. If I fill the vessel with a gas, the piston can compress it an enormous amount before it gets to many thousands of PSI. Just think about a "66CuFt" SCBA tank. Is it actually 66 cubic feet inside? No. It's about 2 cubic feet. (Someone probably has the actual volume somewhere.) My point is that they can push 66cuft of gas into a space the size of a large shoebox. Without containment that gas desperately wants to return, as quickly as possible, EXPLOSIVELY even, to 66 Cu Ft. How big is 66Cu Ft? It's a little less than the size of the interior of a VW Beetle. Because you can't really compress liquids if the vessel ruptures it squirts out a little bit until it reaches equalibrium. This is precisely why hydraulic oil systems are able to be used to move and lift heavy things. If the oil compressed none of that would be possible. They reach crazy high pressures, but they don't compress much. The PSI ratings on pipes is for liquid, at 73°F. You have a few things working against you in your calculations. 1) Gases expand...quite a bit, as they get warmer. (this is how gas turbine generators are able to work. A heat source heats water until it becomes steam. Steam expands dramatically in volume. This pressurizes the system it is in. The pressure is used to move turbines that generate electricity. 2) PVC gets weaker...quite a bit, as it gets warmer. 3) Compressing a gas causes it to heat up, this heats up the containment vessel too. (See problems 1 and 2 in the context of problem 3?). 

To answer your original question though, Force = Mass * Acceleration

You know the mass of your projectile, you can probably figure out the acceleration if you can get your hands on a chrony. Then you can calculate force. You can find the mass and velocity of .22LR rounds readily on the net.


Edit: I should point out that hydrualic pressure systems aren't harmless either. They can shoot hydraulic fluid out of a pinhole leak at high pressure psi that will cut like a laser. Not explosive though. Sometimes they utilize gas pressure accumulators to maintain pressure and those can explode. That's why they're enclosed inside heavy steel chambers.
 
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