For one, don't buy from evike.
http://lmgtfy.com/?q=evike+horror+storiesFor two, I'm pretty sure the CQR has a 300mm inner barrel (unless you measured it, it's very possible that I'm wrong). They don't make inner and outer barrels to every length specification, just for M733, M4 Carbine, M14, etc. so it would be difficult to find one that came out to exactly 423mm. Like whoever said it said, it doesn't make a huge difference in accuracy. Unless it's a precision inner barrel like this one:
http://www.airsoftgi.com/product_info.p ... ts_id=7299 I'm not saying this one is the best, I don't have any Madbull products in my gun.
What I'd do and am planning to do with my GR15 is get an M733 outer barrel and a Madbull Gemtech Blackside so that there is a bit of room between the end of the inner barrel and the end of the barrel extension (it's a standard M4 length barrel which is 363mm). For you it would be a 363mm inner barrel and a barrel extension.
Barrel extension:
http://www.airsoftgi.com/product_info.p ... ts_id=2357(one of many) Inner barrel:
http://www.airsoftgi.com/product_info.p ... ts_id=1233(like I said, I don't have any Madbull products on/in my gun, but I've heard reasonably good things about them)
I think KWA guns have threads underneath the orange tips (someone correct me if I'm wrong) but if they don't then you'd need an outer barrel with threads:
http://www.airsoftgi.com/product_info.p ... ts_id=7918 (need I say it again?) They have them cheaper and more expensive, depends on budget, personal preference, etc.
I'm no gearwhore. I prefer "Connoisseur of Fine Tactical Garments".
See me? No? Good.
According to society, I'm too retarded to have life.
"I don't think he knows we're here..." *POP POP POP* *HIT!*
What's gonna work? DUCT TAPE!
$tealth