# pneumatic guns?



## ucf_motorcycle (Jul 12, 2008)

Anyone use one? They look like they would be very fast and easy to reload. I just wonder why they are not more popular. 

I was looking at the Mares Sten but I am heesitant as I have never tried one or know anyone who uses a pneumatic.


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## Firefishvideo (Jul 1, 2010)

ucf_motorcycle said:


> Anyone use one? They look like they would be very fast and easy to reload. I just wonder why they are not more popular.
> 
> I was looking at the Mares Sten but I am heesitant as I have never tried one or know anyone who uses a pneumatic.


 Would be nice for shallow water/small fish.....flounder,sheephead,ect. They don't have the power of the larger-band powered guns, and since they rely on air power....they are handicaped when used at the deeper depths that we have in this area.
Its hard to improve on the rubber band driven design without giving up reliability,power,and simplicity.


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## ucf_motorcycle (Jul 12, 2008)

Are you saying when you get deeper the air volume will be compressed so it won't be as powerful? I didn't think of that I guess if that is true it would not be a good choice for here.


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## Firefishvideo (Jul 1, 2010)

ucf_motorcycle said:


> Are you saying when you get deeper the air volume will be compressed so it won't be as powerful? I didn't think of that I guess if that is true it would not be a good choice for here.


 Exactly right. As you go deeper, the water pressure increases, but the pressure in the gun remains the same....so it will shoot with less force.
Besides....if you ever intend on taking some of the monster red snapper around here, you will want the power and shaft size of a 48'' rubber powered gun.:thumbsup:


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## markhsaltz (Aug 2, 2010)

Actually the pneumatics are more popular over seas. They have more work records than bands..The longer ones are more of a pain to cock as the shaft must be compressed into the gun from the muzzle. hence the length of the gun doubles at the start of the reload..very tricky for us short armed dives...As far as loss of power I'm not so sure.. It has been a long time since I used the big ones.. I don't remember that being a problem, no more than the loss of power from the bands losing power because they too are being compressed so a it now becomes a thinner band..The nice thing is different strokes for different folks. I will end this with, usually go with what the locals are using..There is a reason they are using this...


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## Firefishvideo (Jul 1, 2010)

Sorry Mark....I do dissagree.....air is compressable at depth.....rubber not. I believe that rubber bands retain the same amount of energy independent of ambient pressure. There is no significant gas volume in the bands....so there is nothing to compress. A change in viscosity of the surrounding liquid would have an effect, but that does not happen to water because it also cannot be compressed.
Sorry if I mis-understood your point......and I have been known to be wrong once in a blue moon......Do you have some knowledge of rubber compressing under pressure? ....I know neoprene does....but that because its full of air pockets.
The way I understand it is that the air powered gun has to use its pressurized air to push a piston ......as you descend an additional 14.7lbs of pressure resists that piston for every 33ft you descend. ...so when I am spearing snapper at 120' I would have 60psi of pressure pressing IN on the piston. The gun is pressurized to 300psi..so I have LOST nearly a quarter of the force exerted on my spear. its probably worst than that, because of the loss of usable volume due to the compression.....the volume of gas you started with at the surface would be effectively be reduced to 1/5th the original volume!!!
----To simplify....air...good in shallow water (overseas)....bands....good in deeper water (Pensacola).


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## Firefishvideo (Jul 1, 2010)

Dang it!....I was wrong.....partially.....i just realized that the math on the volume reduction does not work because the volume did not start at ambient pressure. Since it started at 300psi....its volume would not be affected until the outside pressure reached 300 psi.
....You do still loose 1/4 of your power due to increased abient pressure though.
....also, these guns might be more popular in other countries because it is illegal to spearfish on SCUBA.....which means you will only be hunting on a single breath of air.


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## markhsaltz (Aug 2, 2010)

Great to debate..I too have to disagree. and I'LL be the first to admit i am an idiot about all this science stuff. My understanding is that air in a rigid container DOES NOT compress. The reason a tank of air is shortened by the ambient pressure is because it is OUR LUNGS that need 2x 's the air at 2 atm, 3x's at 3 atm , etc. I know you to be a highly intelligent and experienced diver. I apologize if I am wrong and in no way mean to call you out on this..Just adding food for thought...Hope I get to dive with you one day... BTW, I used to shoot some really big fish off the LA oil rigs in the 70's and used both pneumatics and band guns..I never really prefered one over the other. I still am amazed at the use of mono here when rigging guns since most dive wrecks which has the same line cutting abilities as an oil rig...But I do know that there is a reason locals rig a certain way..any thoughts on what would be a good in expensive scooter to buy. I haven't really used any since the 70's when I used the big farrallons...


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## sealark (Sep 27, 2007)

I have used pneumatic guns on and off since they came out first one was a US divers back in the 60s. They are more powerful than rubber guns and do loose a very small amount of power with depth but it isn't noticeable. The big thing like stated is cocking them I can't do it at all at my age any more. Another bad thing is the maintenance. O-rings are a bitch to change and go bad often. A good rubber gun would be my suggestion the price would be comparable to a pneumatic and last years with just rubber replacements and general maintenance.


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## Firefishvideo (Jul 1, 2010)

Hi Sealark! What was the biggest fish you ever took with a pneumatic gun vs. rubber powered? I'm sure Sealark has tested more gear that I ever will. I would pay close attention to his advice on the maintenance issues. You can easily maintain a rubber powered gun yourself.....maybe not as easy to rebuild a air powered one.

-Mark- I would agree with the sealed container volume....except that it is attached to a valve and piston......which effectively opens the container every time you pull the trigger. O-rings seal it from water intrusion, but with the valve open and the piston exposed to exterior pressure....it is no longer a pressure proof system.
Even a scuba tank is not immune to this. If you take the lungs out of the equation.... and take the tank/reg to a significant depth....it will cease to supply air when the exterior pressure approaches the interior pressure. If your your reg does not compensate for the pressure increase.....you will also feel it slow down its delivery of air long before the equilibrium point is reached.


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## WhackUmStackUm (Jan 31, 2010)

I like sealark's feedback. Good practical advice.

Here is my two cents on the science stuff:

It seems to me that whether bands are compressed or not at depth would have little effect on their strength. It is my understanding that the energy stored in the bands comes from stretching the molecular bonds of the rubber. These bonds would remain under tension even at depth. I have speared fish at 250' and the bands seems to be just as effective. Whether the diver was effective at that depth is another discussion. 

The effective power in a pneumatic gun at a particular depth is related to the difference in pressure on the driving piston inside the gun and out. As depth increases the pressure difference decreases, reducing the effective power. As sealark mentioned, the effect would be slight at recreational diving depths. A 300 psi gun would only lose approximately 1/8th of it's effective psi at 83', and 1/4 of it's effective psi at 165'.

It might be fun to build an automatic or semi-automatic pneumatic gun that fires inexpensive darts and is plumbed into a scuba tank and balanced 300 psi regulator.


Whack 'um


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## sealark (Sep 27, 2007)

Firefishvideo said:


> Hi Sealark! What was the biggest fish you ever took with a pneumatic gun vs. rubber powered? .


300 lb Jewfish back in the 60s when there were no regulations.


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## Firefishvideo (Jul 1, 2010)

sealark said:


> 300 lb Jewfish back in the 60s when there were no regulations.


 :notworthy:


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## markhsaltz (Aug 2, 2010)

Acyually NO AIR escapes the tube..It is sealed UNLESS there is a leak. I agree bands are easier to fix yourself..More diversified in that if you need more power change the size or power of the bands..My pnuematics have lasted over 10 years w/out any problems.. I did have one leak and I couldn't fix it.. I sent it back to Cressi and they couldn't fix it..However, 3 years later I did befriend their main repairman. When I told him about my gun..He promptly sent me a brand spanking new one..BTW, I need to meet you so I can pick your brains about white balancing U/W video. I just got a new (used) LMI Mako digital . Time to get seriuos about shooting U/W video..


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## markhsaltz (Aug 2, 2010)

My biggest was 400 plus Lb'er. back in the 70's when we didn't know any better..It is my understanding that MOST rubber has some air in it..Wetsuit material is injected with nitrogen for insulation..This info comes from a friend who designs tires for Goodyear in Alabama..also, anything that is stretched for any length of time looses some memory hence loss of power..But, I really don't care..hahaha..time to talk about shooting pics/video..


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