That is very strange you are having so many problems with a stock marui barrel. There should be no problems with the hop unit and the plastic barrel in any way... they are designed to work perfect and i have not heard of one that didn't work or fit. If anything the metal barrels are worse and subject to more problems.
Also, for the lugs, if you are using the plastic barrel you dont need to file EVERYTHING off the lugs... the plastic will wear and eventually sit where it needs to be... THEN it will wear out more and then you replace it with a metal barrel or another plastic one.
As for my fix with the hammer n blowback housing catching:
the hammer has two little teeth on it (near the hammer strut)... top tooth is for half cock position, and the second tooth is for full.
I noticed that my blowback housing would push the hammer far enough down (to the point where it should engage the 'full tooth'. Sometimes it caught it, sometimes it didn't.
Also, i noticed that when it did catch it, there was a substantial gap between the hammer and blowback housing. So, in this situation (this is not the big secret fix to all problems) but what I did was shaved the 2nd tooth (full cock) down. I made it shorter so the hammer didn't have to be pushed down as far when the blowback housing interacted with it.
There is a sweet spot for doing this!!!
Too much filing and you completely screw everything up. Take too much material off that tooth and your hammer will engage the full cock position and be sitting right under the blowback housing and every single time it will get stuck.
Last edited by apilar; February 12th, 2014 at 22:12..