Fact or Fiction

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets. No home made BB or airsoft guns should ever be used in a match where you shoot other people... they are too powerful.

Postby fullmetaljacket » Wed Jan 24, 2007 11:11 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">I guess this Gamo rifle is not a pre-charged pneumatic rifle like we tend to think of them here, but doesn't it ultimately fire the projectile with compressed air? Is there some sort of spring loaded "thingy" flicking it out the end of the barrel. I guess I don't know how spring piston airguns actually work.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

click on this little <a href="http://www.arld1.com/pistonpelletdynamics.html">flash animation</a>, it explains exactly the inner workings of airguns like the Gamo.
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Postby BigBang » Thu Jan 25, 2007 12:29 pm

Ah, I think I've got it. The compression takes place AFTER the trigger is pulled, and the increase in temperature can potentially ignite some of the lubricant in the cylinder via the Diesel effect.

Interesting! You've taught me something!

But, would Gamo use flammable lubricant purposefully to exploit the Diesel effect? Seems like that would cause the gun to be damaged, or at least wear out more quickly than expected.

Something seems funky if Gamo is relying on compressed air alone.
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Postby fullmetaljacket » Thu Jan 25, 2007 3:10 pm

It's not just el gamo, all spring pistons rely on lubricant detonation for power to some extent, the critical element is that it's just the tiny amount of vapor caught in front of the piston seal which detonates.

One way of aiding this effect is putting a drop of diesel fuel in the skirt of the pellet before loading, you'll get almighty bangs and an increase in velocity, but it's a very good way of ruining your piston seal, as well as potentially distorting or even blowing open the compression chamber.

Interestingly however here was a rifle that actually made use of this effect by deliberately injecting ether into the chamber, the <a href="http://www.pyramydair.com/blog/2006/05/weihrauch-barakuda-el54-ether.html">Wehrauch Barakuda</a>.
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Postby SPG » Thu Jan 25, 2007 4:44 pm

Don't forget as well that we're talking about air being compressedin milliseconds. Even without any dieseling going on inside the rifle there's a terrific amount of heat generated.

It's always been said on here that one way to get pressurised airto exceed the speed of sound would be to heat it, and one efficient way to heat air quickly is to compress it from normal atmospheric pressure to 2-3k psi in 7 or so milliseconds.

That's how these spring guns get their impressive results, not through forced dieseling.

The Airforce Talon is a different kettle of fish though. As an owner I can confirm that with the right pellets I can get chroni readings over the speed of sound. I presume that this is a measure of lightness of pellet and extreme high pressure air, but I wonder too if the valve design with its tiny ports creates friction in the air as it passes through, and this in turn creates heat, which then gives us our very hot (and supersonic) air.
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Postby fullmetaljacket » Thu Jan 25, 2007 11:27 pm

<blockquote id="quote"><font size="1" face="tahoma,verdana,arial" id="quote">quote:<hr height="1" noshade id="quote">That's how these spring guns get their impressive results, not through forced dieseling.<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

Don't dismiss the importance of "forced dieselling" - A certain Dr. Gerald Cardew, a known UK authority on the science behind airguns, describes in his book "Airguns from trigger to target" a series of experiments with springers fired in an oxygen-free environment and found the power to be significantly lower without lubricant detonation.

The Airforce Talon (gunpower stealth/storm in your case presumably ;)) has one of the most efficient valve designs on the market as far as PCPs go, which accounts for its remarkable performance. Regarding PCPs and supersonic velocities, I had started a <a href="http://www.airgunbbs.com/forums/showthread.php?t=35263&page=22&highlight=supersonic">thread</a> in a UK airgun forum which ultimately resulted in Ben Taylor (the Ben in <a href="http://www.theoben.co.uk/customer/home.php">Theoben</a>) losing <a href="http://www.airgunbbs.com/forums/showthread.php?t=70658&page=15&highlight=supersonic">a 100 quid bet</a> when it was proved that supersonic PCPs were more than possible. If you look through the threads there are pages upon pages of different theories as to why this is possible.
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Postby clide » Fri Jan 26, 2007 1:38 am

How much dead space does the Talon have? I think D_Hall's last theory on supersonic PCP seemed pretty plausible. The rapid compression of dead space creates a little pocket hot air near the projectile to give it enough of a boost to go supersonic. If the Talon has more dead space then other PCPs it would provide some credibility to the theory.
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Postby fullmetaljacket » Fri Jan 26, 2007 2:32 am

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Postby BigBang » Fri Jan 26, 2007 10:52 am

PCP = "Pre-Charged Pneumatic" ????????? (I don't recall the term, sorry).

Really fascinating stuff, guys. Lots more for me to study. Sounds like Gamo's claims may indeed be plausible. I though they were maybe just hyping up their new rifle to boost sales. I'll have to keep this one in mind when my wife finally agrees to let me buy our little boy his first rifle. My first rifle (6 yrs old) was a Sheridan .22 pellet gun my Dad bought from one of my older cousins. I still have it, but it was/is a bear to pump up.

BTW - Hawkeye: Do you own a fire piston? I've poked around the net and haven't really found suitable plans. There are many for sale, but they seem to be pricey.
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Postby fullmetaljacket » Fri Jan 26, 2007 11:46 am

precharged pneumatic - an air rifle that uses a pre-charged reservoir (from a separate pump or diving bottle) to fire multiple shots, as opposted to a single/multi-stroke pneumatic with an on-board pump like the sheridan.

I doubt the Gamo would be very good for a young shooter, it must be hell to cock at those power levels and the recoil (and dismal trigger...) will make it extremely difficult to shoot accurately.

PCPs require ancillary equipment and are generally more expensive, but there's just no comparison - recoil-free, mostly quieter than springers and can go up to much higher power levels without a corresponding strain on the mechansim. My <a href="http://localhost/forums/viewtopic.php?t=15100">Daystate Mk.3</a> will happily shoot pellets 6 times heavier than the Gamo at 900 feet per second, with no recoil and minimal noise, even without a silencer. With the latter fitted, you literally only hear the pellet impact downrange :D
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Postby An Apple Pie » Fri Jan 26, 2007 1:11 pm

Where can you get those tanks that come on the Talon, Condor, etc... Filled?
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