I'm running an AEG with a CQB outer barrel and a custom barrel extension (roughly 2 inches) bringing me to about a 340mm - 350mm inner barrel length (roughly give or take)
I was going to cut down a Madbull Python but after reading this post looks like im better off with something steel - but again after some of these posts, not to cut it at all!

(dont have the crowning tools)
Doesn't look like anything 340mm - 350mm exists premade on the market today however this Prometheus looks to be as close as i can get - however its made specifically for the Masada..it doesn't look any different? Not sure if its compatible with fitment.
http://redwolfairsoft.com/redwolf/ai..._11_5_inch.htm