Heatsink on a pistol mag?

[Yuri]

I've been thinking about this and it seems that a variable volume gas reservoir would pretty much defeat the entire purpose of having a gas gun in the first place.

 

The evaporation of the propellant happens inside the magazine. The liquid propellant will stay at the bottom of the magazine at all times and will not come out of the reservoir unless you hold your gun upside down or something. The amount of liquid gas in a bottle or a magazine depends on how full it is. The gas to liquid ratio in a full, commercially sold can of propane should be something like 20% gas and 80% liquid. It seems to me that this sould also be the ratio that exist inside a full magazine, as long as the mag was filled upside down. Even though a magazine filled right side up will initially have the same pressure as one filled correclty, it will only be good for a few shots since there is no liquid gas to evaporate and thus 'top off' the pressure.

 

Let's say that we have a magazine where the bottom of the gas reservoir is a movable piston. Now if every time we fire the gun we move the piston up before the liquid gas has a change to evaporate and reach equilibrium on it's own, there will be no phase change from liquid to gas and we have indeed solved cooldown. However this is hardly ideal, since as the piston moves up, and as the volume taken up by the liquid gas stays constant, we will hit a point where the liquid gas reaches the top of the gas reservoir. This is effectively the same thing as firing the gun upside down and we all know how well that works. Also the piston is doing all the work and we could replace the gas with air. So we end up with what is effectively a springer.

[Punkypink]

Well, my idea for a variable volume reservoir also takes into account the need to maintaining the propellent in a partial liquid and partial gaseous stat.

 

Its really not conceptually difficult to imagine a variable volume reservoir that varies enough to maintain the propellent in mostly liquid state, but doesn't vary to the point that ALL the propellent stays in liquid state. The piston is of course restricted so that at a certain volume of propellent left, it no longer gets smaller, and the rest of it just converts itself into a gaseous state, thus there will NOT be a point where the propellent reaches the valve at a liquid state. How come its so hard to understand? Am I getting something wrong here?

[Yuri]

Am I getting something wrong here?

 

Not really. It's just that if you have a full mag of gas and you wan't to use it all, that liquid has to evaporate. So the cooling has to happen. What you can do with the variable setup is to control when it happens, but you can't take it away altogether.

[Punkypink]

Not really. It's just that if you have a full mag of gas and you wan't to use it all, that liquid has to evaporate. So the cooling has to happen. What you can do with the variable setup is to control when it happens, but you can't take it away altogether.

Yea thats my point. Have a system that allows for some evaporation but reduces the cooldown effect. I'm sure MOST if not all of you would rather the cool-down happen slower and later right?

[Stealthbomber]

FWIW, I'm not sure the variable-volume thingummy is practical.

 

To begin with, you don't get something for nothing.

You have to assume that the gas pressure inside the mag starts off high enough to pressurise your variable-volume thingummy.

For the sake of argument let's assume this to be a cylinder with a spring-loaded piston inside it.

The gas vapour inside the gun pressurises the cylinder and compresses the spring behind the piston.

Shooting the gun makes the mag cold so the gas doesn't vapourise to the same pressure again.

This allows the spring to push the piston up slightly and restores the pressure to the original level.

Further shots drop the temperature more and, as a result, the spring can push the piston further and further up each time to restore the pressure to the original level.

 

This WOULD work but would probably require a cylinder of equal size to the actual mag.

And you're going to struggle to fit that inside a pistol.

 

Now, you could simplify the system slightly by having a bladder of some sort inside the mag permanently pressurised to, say, 4 bar.

When the gas pressure is 4 bar or higher it'll compress the bladder but, once the pressure drops below 4 bar, the bladder can expand and restore the pressure to 4 bar.

Course, to continually do this in a meaningful way the bladder would probably need to take up at least 50% of the volume of the mag.

Would you rather have 70 shots with 30fps difference or 20 shots with 5fps difference?

 

Incidentally, this reminds me, a while back people were bunging rubber balls inside mags with the aim of helping with this.

As long as the ball is made of something that can absorb heat it will help in two ways.

It'll reduce the amount of gas in the mag and, thus, reduce the amount of energy required to heat the gas after every shot and it'll also help transfer heat into the gas.

For maximum effect I guess you could fill the mag with diamonds.

Obviously this sort of thing requires that the empty mag is left to return to ambient temperature before being reused in order to remain effective.

 

Regarding passive heat sinks, the ambient temperature wouldn't be a huge deal.

It's not really about the ambient temperature. It's about the differential in temperature between the air and the gas inside the mag.

Firing half a dozen shots can easily lower the gas temperature to below freezing.

The problem is that the flat walls of the mag clearly don't gather, conduct and induce enough heat into the gas inside the mag.

A heat sink, particularly an internal one, would allow more ambient heat to conduct through the mag and into the gas and allow it to heat up again more quickly.

Unless the temperature outside was below about -30 you'd always get some useful heat transfer.

 

Personally, I reckon the only viable improvement would be made by cramming something inside the mag.

Maybe filling the mag with wire wool would be the way to go?

That'd creat a large surface area inside the mag and allow the heat transfer to happen far more efficiently.

[Punkypink]

To be fair, the one big draw back I could think of was that it would make the magazines very propellent specific, since the amount of variation in volume would be finely adjusted to a certain type of propellent used.

 

Other drawback being that it would make magazines a lot more expensive.