Metal body installed on m4, now no auto?

[jcheeseright]

Hi,

Just installed a madbull metal receiver on my M4 (marui), and I'm pretty sure there's something funky going on with the selector plate. When the gearbox is out of the gun, I can change between semi and full auto with no issues, the same also with the gearbox just mounted in the lower receiver with both pins installed, however, once I put the upper receiver on and secure it with the front pin selecting auto no longer works. The selector switch goes all the way over, no problems there, and the selector plate is moving (I can see it through a small hole in the receiver), but the trigger pull becomes really heavy after a couple of mm and once you overcome it there's a loud ish click. Occasionally after switching from semi to auto the trigger will pull 'normally' but there's a click halfway through.

Anyone have any ideas?

 

[kungfumonkey]

is there any marks on either the selector plate or any of the internals that are fresh as could be as simple as a clearance issue when the trigger is engaged which could be knocking the selector out of position?

fyi i have no experience just trying to offer a hand

 

[jcheeseright]

No, no extra marks, even bent the lower receiver out a little to make sure the selector plate had plenty of room to move without scraping on the body. I'm super confused by the whole thing, there's stacks of room for it to move, the selector switch is fine too.

 

[jcheeseright]

problem solved, shaved a couple of millimetres off each end of the selector plate and it's all working perfectly now!