BBMG Propane Air Rig Build

[nicksam112]

Hell everyone

Seeing as I couldn't find much information or plans about using propane as an air source for a BBMG, I decided to go ahead and build one myself and test it out. If something similar to this has been posted before I apologize, but hopefully I can provide some new information.

Propane is perfect in the sense that at reasonable temperatures from 60-90 degrees it maintains a pressure of 100-150 psi, (exact pressure-temperature here http://virtualmark.net/wx/pressure.htm) which was the pressure I was aiming for since it's easy to control and regulate. Propane tanks are also really cheap.

However, like all good things, it has it's downsides. Mainly that it expands relatively slowly and that that is, of course, flammable. However given that it's commonly used for airsoft, I felt that it was safe enough as long as I didn't fire it around any BBQ's. As for the expansion issue, I used a smallish expansion chamber which was suitable for shooting in 3-5 second bursts.

Here is an imgur album of the build with some additional details on it's construction: http://imgur.com/a/88Y7A

Overall it cost around $40, but that includes the $10 I had to pay for the 1/4" NPT tap and die.

I feel this is a much cheaper and more accessible air source than CO2, especially if used in moderate temperatures. However, under 40 or above 90 degrees Fahrenheit it becomes nearly useless and or potentially dangerous. PVC pipe is not meant to be used at pressures much higher than 140 PSI as far as I am aware so above 90 degrees the expansion chamber could potentially burst harming you or others.

Hopefully this information proves useful to others, and please be careful. High pressure and flammable gas is not a combination to be taken lightly. :bom:

Feel free to ask questions, I'll try to answer them to the best of my abilities!

[fenrir]

Propane is cheap, but air is free. If you are only using pressures below 150psi, you might as well just stick to a backpack air supply or something like that.

[noname]

The problem with a backpack full of air is that it won't liquefy unless it's a nice chilly 77K outside.
This isn't the case for propane, which will continue to evaporate in the tank as it is being extracted.

If only propane didn't smell like butt...

[nicksam112]

The problem with a backpack full of air is that it won't liquefy unless it's a nice chilly 77K outside.
This isn't the case for propane, which will continue to evaporate in the tank as it is being extracted.

If only propane didn't smell like butt...

Yup, air tanks are nice but they don't last long. Propane tanks contain a surprising amount allowing you to keep going and going and going.

Yea, but hey it's way cheaper than CO2 so I can't complain

[cammyd32]

Nice job on the build,
I've always wanted to use propane as a source of power, as the amount of shots you get for such a small moderately low pressure chamber, it really does seem appealing in comparison to expensive co2 or dangerous HPA.

I'm sure you have probably considered this already but, you might want to be careful to avoid longer bursts of fire, as the rapid expansion from to cylinder might be enough to lower temperature in your expansion tank enough to make the PVC dangerously brittle, or alternately freeze the reg up good.

[nicksam112]

Nice job on the build,
I've always wanted to use propane as a source of power, as the amount of shots you get for such a small moderately low pressure chamber, it really does seem appealing in comparison to expensive co2 or dangerous HPA.

I'm sure you have probably considered this already but, you might want to be careful to avoid longer bursts of fire, as the rapid expansion from to cylinder might be enough to lower temperature in your expansion tank enough to make the PVC dangerously brittle, or alternately freeze the reg up good.

Thank you! It does seem to be an ignored alternative, hopefully some more people will look into using it

Oh yea, fortunately though the pressure usually drops significantly before temperature really becomes a concern. Honestly the PVC expansion chamber is the wink link, if I could get my hands on schedule 80 PVC (with twice the pressure rating!) then I'd be one happy camper.

[Boomer58cal]

Nice job on the build,
I've always wanted to use propane as a source of power, as the amount of shots you get for such a small moderately low pressure chamber, it really does seem appealing in comparison to expensive co2 or dangerous HPA.

I'm sure you have probably considered this already but, you might want to be careful to avoid longer bursts of fire, as the rapid expansion from to cylinder might be enough to lower temperature in your expansion tank enough to make the PVC dangerously brittle, or alternately freeze the reg up good.

Thank you! It does seem to be an ignored alternative, hopefully some more people will look into using it

Oh yea, fortunately though the pressure usually drops significantly before temperature really becomes a concern. Honestly the PVC expansion chamber is the wink link, if I could get my hands on schedule 80 PVC (with twice the pressure rating!) then I'd be one happy camper.

Great idea! I just posted my first bbmg in the showcase section. When I get a chance later this week I'll try running it off one of my propane meters and see how it works. I need to pick up another chronograph. I'm interested to see the difference in velocity between compressed air and propane. I also happen to have a few feet of 2' sch 80 laying around, so maybe I will use it on a dedicated propane build.

[jackssmirkingrevenge]

The problem with a backpack full of air is that it won't liquefy unless it's a nice chilly 77K outside.

If only propane didn't smell like butt...

It doesn't, but if it didn't, more people would die in gas explosions.

[nicksam112]

Great idea! I just posted my first bbmg in the showcase section. When I get a chance later this week I'll try running it off one of my propane meters and see how it works. I need to pick up another chronograph. I'm interested to see the difference in velocity between compressed air and propane. I also happen to have a few feet of 2' sch 80 laying around, so maybe I will use it on a dedicated propane build.

Let me know how it goes!
The more results the better

It doesn't, but if it didn't, more people would die in gas explosions.

We have enough Darwin Award contenders is this world as it is, so the smell is a small sacrifice

However any thoughts to the rig as a whole? Maybe the lower cost for a reliable air supply could spark some more interest in BBMG projects. I remember my main problem was always finding a feasible and cheap air supply, dropping 100 bucks just to get started with CO2 never seemed especially appealing...

[NeoSpud]

We have enough Darwin Award contenders is this world as it is, so the smell is a small sacrifice

However any thoughts to the rig as a whole? Maybe the lower cost for a reliable air supply could spark some more interest in BBMG projects. I remember my main problem was always finding a feasible and cheap air supply, dropping 100 bucks just to get started with CO2 never seemed especially appealing...

I've personally tried running a BBMG off of propane, as well as computer duster, with very poor effects. I know that CO2 is a tough initial sell but once you have the regulator then it's a piece of cake. A 5lb tank refill is 10 bucks, which is totally acceptable when you consider the price of airsoft BBS, right? I recycled my BBs but otherwise I'd be shooting 50k a day if I was running my gun lightly! In other words, if you're going to be shooting airsoft BBs from a BBMG, then the air consumption rate is not a problem if BBs are your limiting factor!

Don't hesitate to email if you have a question; I'm hardly ever around but if I get an email notification I always answer it!

[jackssmirkingrevenge]

Monsieur Plow?! What brings you out of the woodwork