I have a KWA g36c. Granted it doesn't come with a k-rail and scope the internals are absolutely bomb proof. It's basically pre-upgraded. All you need is a tightass barrel and you're good to rock. The k-rail scope is pretty crappy, but if you really want one you can get it from rsov.com for 40US plus ship or from huang 60CAD plus ship or the new ares dual optics k-rail from rsov 90US plus ship. I personaly like the C-rail better and mount a bushnell holosight with eotech 4x fts magnifier.