Propylene: Cold-Weather Gas Solution

Propylene gas is the way I generally get my GBB pistols and rifles to operate with higher round counts and less cool down issues in the colder months of the year – a lesser known secret that I’ve been experimenting with and have only shared locally with “Jester” until now.  Both of us have used and confirmed findings with Propylene and success in (a) my WE M4A1 OB, (b) his old KJ / TK M4A1, and (c) a variety of my gas blow back pistols.

This is a solution I’ve been testing since 2011 as a way of making my GBB’s viable options to shoot with during the winter weather. Since not all GBB systems have CO2 magazines readily available that work with them (without breaking things) or that are actually reliable (most of which are not), a gas that uses a higher pressure seemed like a good idea. I’ve read about Airsoft players (mostly from the UK) using this on and decided to give this a try for myself – the following is a summary of my take on the matter of Propylene in GBBs:

Currently available as MAP/Pro or under other names, these gas-filled tanks are often sold for usage with propane torches, as they can heat, solder and braze at higher temperatures – this does mean that the threaded connection is the same as that found on propane tanks, meaning that Airsoft Innovations Propane Adaptors fit perfectly. As with Propane and Adaptors, Propylene should also be used with silicone oil (the effectiveness of this mixing process is generally questionable at best, but at least its better than no oil at all).

The higher cost of Propylene is not ideal when compared to that of Propane. That being said, some older designs of gas systems, such as those from many of the common TM pistols and all their multitude of clones, just don’t operate to my desired level in cold ambient temperatures. This often results in increased and quickened cooldown effects; though this can be solved by short loading one’s GBB magazines, I do like to load more BB’s and carry less magazines if at all possible (less weight and less things to get lost). Use of Propylene in these less efficient systems generally seems to reduce cool down to be much less noticeable, no matter what the ambient temperature is. Use of Propylene in warmer temperatures also often results in more perceived recoil as the gas pressure is higher.

Propylene exerts a higher pressure of 167 PSI, whereas Propane and Green Gas are at 131 PSI (and for reference, CO2 is 827 PSI) at 20 degrees C (SATP) – these numbers come from research conducted by user “Kullwarrior” on Airsoft Canada (Kullwarrior has been doing experiments of his own with Propylene for quite some time). I find that in (somewhat) controlled experiments I’ve conducted, this can result in anywhere from an 5-50+ FPS increase, depending on a variety of factors in regards to the gun itself. For example, in my upgraded WE OB M4A1 with DIY velocity reducer, hop up upgrade and tight bore barrel, I generally get an increase of 50 FPS as compared to Propane in the same ambient temperature.

Propylene allowed me to use Green Gas magazines for my WE M4 (closed bolt and open bolt systems), as well as a variety GBB pistols from Tokyo Marui and clones (however, KSC System 7 and KWA NS2 guns seemed to have little to no noticeable benefits), rather than having to purchase CO2 magazines which I have generally found to be rather prone to leaks that cannot be fixed. More often than not, I’ve discovered that the higher pressure of gas tends to either blow out magazine seals or blow up loading nozzles… though I’ve had other nasty results including (but not limited to): plastic slides that turned into flying bits of frag near my face, cracked hop up chambers, and frozen/dried out/cracked gaskets causing loss of gas pressure in the system.Do note that I have yet to test Propylene with non-blow back designs, such as the KJ M700 which uses Tanaka’s Pegasus system – but that’s on my list of next purchases and things to test. I’m not sure if much research has been published about this on forums or blogs or whatever by other Propylene users, nor have I looked into this matter, to be honest.

In summary, Propylene is:

  • Good for higher FPS
  • Good for usage in colder temperatures
  • Bad for blowing up GBB loading nozzles
  • Bad for going over approved safe FPS limits

Note: I am in no way responsible for any damage that this may cause to your gun(s). I’ve done the research to educate myself about the many risks that result by using the higher pressure Propylene gas in gas gun systems that were initially designed to operate on HFC134A – not HFC22 or Green Gas (which already pushes the reliability of many GBB and some NBB models to their breaking point) – I strongly suggest that you do the same due diligence before attempting to use MAP gas in any of your own gas guns.


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