So I am building a new gun and want to buy a real MagPul Industries ACS-L collapsible stock. I have done a lot of research on the net and from what I have gathered, the majority of airsoft guns accept Mil-Spec stocks. Here is even a guy who bought a Mil-Spec CTR for his AEG. Here is a photo displaying the difference between Mil-Spec and Commercial Buffer tubes. And here is my buffer tube on my 416(approximately 6.7" in length) So as of right now I plan on buying a RS MagPul ACS-L collapsible stock. Does anyone have anymore information on this topic or has access to a RS collapsible stock and a airsoft gun to do a test fit?