Winter comes, and then it goes, yet MK23 members remain out on the field throughout it much to the disbelief of other players around them. Every year the discussion arrises between new players and old on how to maintain usability of their MK23's during the colder climates when temperatures drop below the dreaded zero. The answer, much like a good cheese, lies in the smell. PROPYLENE GAS (C3H6), otherwise known as MAPP or MAP/Pro is an industrial burning gas much like propane (which is evident in it's chemical formula (C3H8), and has for some years, been used by savvy players during the colder months to power their GBB weapons. Players often first discover the use of MAPP gas on a field when the distinguishable stench of the added scent fills the air as a player charges their magazine from the most commonly used yellow bottle. But what makes people endure the stench and use MAPP over any other alternative, especially propane you ask? Performance.
MAPP gas has one of the highest liquid pressures available to the average airsofter over any other propellant on the market, and it can provide that higher pressure at the same temperatures as propane, allowing it to provide more pressure at lower temperatures than propane. The bottle itself shares the same thread type that commonly used Propane adapters can be used with it, which makes it a very quick swap out from your normal propane bottle.
To really see the difference, you need to look at some of the figures comparing Propane and MAPP: PROPANE: Vapor Pressure: 120 psi @ 70ºF (21ºC) http://www.advancedspecialtygases.com/Propane.html
PROPYLENE (MAPP) :
Vapor Pressure: 133 psi @ 70ºF (21ºC)
As you can see, there's an increase of 13 PSI between the two gases, which on average has reported to increase FPS in gas weapons by as much as 35 FPS compared to Propane in some magazines. 35 FPS is nothing to be sniffed at (especially with that smell), and in subzero temperatures when gas has the hardest time expanding, it can be the difference of effectively propelling your MK23 rounds. To further understand it's applicability in airsoft usage, the community has discussed the subject in quite indepth detail in previous years and is definitely worth reading in the following posts: http://freedomairsoft.forumotion.com/t24-gas-information http://www.gasguns.info/forum/viewtopic.php?f=50&t=6000&hilit=mapp+recoil
The main question as a MK23 owner that you might be wondering, is whether using this gas has any negatives over Propane? The answer is a little grey. During winter usage, the higher pressure should not effect the magazine seals as the colder temperature will ensure that the pressure never reaches its full potential of 133 psi (as this is measured at 70 F degrees), however in warmer temperatures, the seals will be subject to the higher pressure and may result in potential leaking. One thing to note is that the Pressure Relief Valve must be secured in any TM magazine before using Propane or MAPP gas. Check out the guides section via the main site overview for details about that modification.
MAPP bottles can be purchased around the world from hardware stores that typically also stock propane, from a price point between 10 - 20 dollars per liter. Propane Adapters (such as this one here) can be bought from around 15 to 25 dollars. If you are having trouble with getting BB's out of the barrel in cold weather, you should definitely give MAPP gas a go.