Systema mechbox to g&p metal body
 

After upgrading the mechbox, I never thought I would have problems fitting it into a g&p metal body.

First, I have to shave the rear part of the lower receiver where there is a rubber padding so the rear body pin hole of the lower receiver would align on the mechbox hole. I had to dremel the mechbox hole as the body pin wouldn't fit and have it flushed to the lower receiver.

Second, the small pin just above the trigger wouldn't insert. The issue is the mechbox needs to sit a bit lower on the lower receiver. I had shaven the bottom part of it (where the trigger comes out) for 3 times and still the holes won't align.

Anyone has this similar issue or who had successfully installed one?

TIA.:D

interesting. the systema gb is almost surely of perfect tm dimensions.

also, make sure to insert all pins before you put on the pistol grip.

Yup, that's what I did. I never thought that I would be having these issues. If I knew it beforehand, I wouldn't have gamble, but I'm already on it...
The pin is a bit offset upwards when half-way inserted.

Used to have a similar problem with a gun I assembled, I made it through by shaving and trying each time.

i have to take this opportunity to plug my favourite receivers. magpul aluminum receivers have always been problem free for me.

Did you only have to shave the gearbox?

installed several systema boxes into G&P bodies, haven't had a problem yet.

I modified the lower receiver and left the systema GB untouched, if it ain't from passing a little sandpaper in the pin holes to slighty oversize them, mostly making them smoother...

Well, I think me and audi_bhoy were unlucky ones in having fitting issues.
Good to know that Amos had done a number of these combo and never had an issue.

I'm not 100% sure though that it was aG&P body, but when I got it the auto wasn't working properly, as the selector plate wouldn't reach the full auto position, that's in part why I had to use the dremel here and there.

I'll try to disassemble the mechbox and remove the selector plate...close the mechbox and install in the metal body. I think this could be an issue, selector plate prevents the mechbox to fully seat on the metal body. If it is, then then half - circle (concave) portion of the selector plate might need shaving...

could be that your trigger assembly screw is tightened too much and applying pressure to the selector plate making it very difficult to move.

You mean the tiny screw that holds the trigger mechanism to the gearbox? If so, then OP just make sure it is not protruding out the gearbox. File off excess if it is.

I had removed the switch plate and tried to fit again and same results. The cut-off lever is good and not protruding outside the gearbox. I'll shave again some area on the mechbox now that the trigger is removed. Hope this gets it done.

...and finally, issue resolved. Thanks for all your help guys.... Merry Christmas ASC!
Will post pics later how the mechbox looks then...