As some of you may know I'm buying the BE SL9 as a sort of project gun, blood, sweat and gearboxes really makes airsoft fun for me. I am however looking for a little help. I have so far only been able to find one web page that sells the fore-mentioned JG/Echo1 G36c gearbox (they don't have it in stock until march), I was wondering if this gearbox matches with the M4 variants or is just hard to find? and maybe a little help finding one would be greatly appreciated.