Well I'm set on getting a SP M40A1 from Jackwarz on this site, however i would prefer a spring cylinder while he only has gas. Thankfully my buddy can probably let me have on of his spring cylinders if i trade him a gas one however i would like to have options if this doesn't pan out. I tried searching online for a spring cylinder even checking at smaller Asian sites such as KIC (which are in Japense/Chinise/etc) with no luck. BUT i did find this site http://www.planetairsoft.net/archives/archive-03-nov.htm which has this interesting bit of info: Also coming soon from PDC, is their gas cylinder kit for the Sun Project M40A1 and APS. These cylinders allow your M40 or APS to be converted to gas powered. Now i know that you can use APS-2 springs but does anyone know if you can use cylinders as well? I'll try anyway eventually but it would be nice to get confirmation.