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Building/Modifying Pneumatic guns

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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New Member
Jun 19, 2020
Hey Guys,
I'm new on DB and new to pneumatic spearguns, so please forgive my ignorance if you think I should know.
Is there anyone who is trying to design and construct a better pneumatic gun among you? I mean from what I've seen, aside from all the experimental guns years ago, the main design that emerged is the standard that we see today. Every brand seems to just have the same thing. I realize it's not as easy to build or modify a pneumatic as it is a band gun but I was curious if any of you were involved in that?
I saw a gun that did not use a piston but rather the shaft was so snug to the barrel that steel on steel acted as the seal and propelled the shaft. Granted once the shaft left a portion of the compressed air was gone too which is probably why they now use a piston. Am I correct? However, even with a piston, why do we have 11mm and 13mm ID tube with 7-8mm shafts? Why not snug it up to be metal on metal like they did before on some guns? If I was to guess, one possibility is that if your shaft bent then the friction would go up a ton. But you would need to fix a bent shaft anyhow.
The other thing that I see in reading these forums is the issue of hard loading at higher BAR. Or loading loading the shaft of a cocked gun. Can't we design a different/better trigger system that won't release when jammed by the shaft? All the trigger systems are the same for these guns, isn't it time we broke out of the mold.
Isn't it typical of a newbie to write something like this?? haha Ya but I'm a designer and would work on my own gun but I travel a lot and don't have the equipment set up to work on stuff nor am I usually in countries that have access to good materials like stainless steel and Delrin. Anyhow, I thought I'd see if any of you were into development and maybe I could share some of my current ideas that could upgrade the system if someone else was tinkering.
Using the search function would save going over old ground as these topics have been thrashed out here over many years. Guns don't use spears that are a very close fit in the inner barrel as the smallest bit of grit will jam them. Hydropneumatic guns have the smallest clearances where say an 8 mm shaft will run in a 9 mm barrel, but the pressure has to be high as only a small cross-section faces the air pressure inside the gun. With some hydropneumatic guns you can do a dummy shot with no spear to clean them out as water is strongly ejected from the gun. As they are likely to corrode internally if you do not keep on top of the maintenance they have pretty much disappeared.
“Loading the shaft of a cocked gun”.
For context. The world has seen over two decades of firearms & weapons regulations, pneumatic guns have dodged the legislation in many countries simply because they are still “muscle powered”. Please be very careful that any “new”? development especially in regards to mechanically cocking a gun doesn’t result in further restrictions under prohibited weapons legislation & regulation.
We have seen posts removed from here because those posting them are innocently unaware that they are breaking firearms & weapons regulations & this may explain why there hasn’t been a great deal of will to invest in this area, your reward could be an unexpected gaol sentence.
Thanks Pete and Sharkey for your response. Sharkey, I will say that any new development in any field risks future regulation of some sort. We have seen that probably longer than two decades. But to not advance technologically due to fear of being regulated seems odd to me. Anyhow, there are safe ways of doing things and stupid ways of doing things. I see where you are coming from and I receive the caution and that reason you gave really could be why there hasn't been much effort in this direction. Well I've just started on the path of checking these pneumatics out first hand. I just ordered my first gun Predathor Vuoto 100. Should get here in 3 weeks.
Mate that first sentence in my last post was a quote from you. That basically refers to an illegal type of speargun which is loaded & cocked mechanically & then the spear is inserted.
Do this in Australia & you face a mandatory sentence of five years. Mandatory means that is what the judge must sentence you too as minimum.
Imo you have already made a mistake by posting that sentence & you should understand why people are cautious before making further comments or proceeding with “developments”.
We have already been through the era of super powerful guns. The carbon dioxide expellable gas guns were very powerful and needed no muzzle loading effort, but were eventually banned everywhere. They could be fired on land and in the water and in the wrong hands were very dangerous. The cartridge powered gun had many forms, the most well-known would be the SMG from Tapmatic Corporation. These too were banned as being firearms. Once you go to muscle power loading that places a practical limit as if you use a multi-band gun with say six or ten bands it takes too long to load it. Pneumatic guns can be powerful by using pumping systems, but the loading time becomes excessive and unless you are after one shot into a monster are not very practical for general spearfishing. The one shot monster slayers were the hydropumped hydropneumatic guns, but they are not very practical for general spearfishing as are usually sinkers. When spearfishing first started there were many scuba spearfishermen and the heavy guns were not such a problem for them. Unfortunately they bumped off all the giant cods and groupers by cornering them in their lairs and blazing away with their super powerful guns, many were selling the meat and so authorities put a stop to that.
SMG brochure.jpg
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Another aspect of super powerful guns is if you catch your hands in the shooting line, such as holding the line loops, the gun can easily rip your fingers off. This has happened a few times with carbon dioxide guns as most of them had a rubbish line system with line wraps stuffed under a passive line finger at the rear which tended to let the line go when you did not want it to.
Ya I read some about those S.M.G.s. I saw a four spear Johnson once that looked nice. Being American means they are still legal back home. But just like band guns where you have to buy bands, you have to purchase the cartridges. That's what drove me to pneumatics because I feel that if properly maintained you don't have to spend as much. The power seems plenty reachable its just that reaching that power with loadability is tricky. I was considering a third chamber...but I won't go into that here. Thanks for the explanations.
Russians have pretty much explored pneumatic guns thanks to a gunsmith tradition before decent guns were made by State factories as they were continually looking for new ideas that would justify the high prices for their custom made guns. The Spanish and Italians were more concerned with production guns, but the latter tried the most adventurous designs such as water surcompressor guns. When the floating after discharge era arrived the only gun that tried yet another idea was the "Mirage" with its unique pump down system that only they produced. The problem with the 40 bar Mirage is that in order to cram everything in the gun and still keep it a floater they squeezed up the airflow passages in the rear of the gun. This had the effect of throttling the gun so that its performance was below what it should have been, plus the all-important three position power controller tended to spring a leak. A better Mirage was possible, but Mares reissued it without changing the rear handle which is where the problems lay. This has all been explored here:

The only reason the hydropumped hydropneumatic guns snuck through the regulations was that they can only operate underwater because the hydropump has to be submerged and the entire inner circuit has to be completely flooded. Like hydraulic lines in vehicle’s brakes any air bubbles and the gun does work properly and produces a weak shot as the air bubble gets squeezed and you shoot off that rather than the air in the high pressure reservoir.
Another reason you don't see that much tinkering or DIY is, of course, that it's much harder to build your own pneumatic gun than it would to make experiments with a wood gun. You need some metal working skills, a lathe, ideally a mill, too. A few are doing it and I think thanks to the internet making it easier to sell worldwide even for an independent builder it is now possible we will see a bit more of this. We have UBL, Tomba (muzzles) and a guy in Italy whose name escapes me.
But overall, pushing the envelope has been left to the big companies and they are conservative and don't see the need to spend R&D money when the oldies still sell.
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