This has not been fired (new gun), and it looks like the trigger is already well used and the hammer is slamming against the front of the receiver (see marks). Is this normal? Anyone else have marks on front of receiver where hammer hit it? Also it appears by barrel does not fit all the way in to the receiver (see gap), is this normal?

Note: I have a LaRue MBT in mine, but I can see the same mark on the receiver in front of the hammer.  On mine, if the upper receiver is not in place and the hammer is not in the cocked position, a lower part of the hammer rests on the receiver.  When the upper is put back in place, the rear of the bolt pushes the hammer back a small amount and the hammer is no longer resting on the receiver, but on the rear of the bolt.  Have your upper with the bolt carrier group in place and the hammer not cocked.  Pivot the upper back into place and see if the hammer moves back.  If the hammer moves back from the bolt, I do not see how it could be contacting the lower receiver during normal operation.  I bet it only takes 1 or 2 times of inadvertently letting the hammer go forward under hammer spring pressure without a bolt installed to make that mark.

Regarding the gap behind the bbl locking lugs...mine looks just like yours, and I've fired 2054 rounds through mine.

Mine looked the same way when I bought it.  

I took it out and shot it for the first time today. It fired fine with no malfunctions. When I pivot the upper down I can see the hammer moving back a small bit. But the hammer now has a line across it where it is contacting the lower. Not sure how that is happening. So everyone else has a mark on theIr receiver and hammer? I'm just worried something is out of spec and this could cause my receiver to crack...

Here is a better pic. So every MPX is doing this correct?

Mine looked like that when I checked it at the dealer when I bought it new and has not changed after 9k rounds

I am thinking we were one of the lucky ones who had this done at the factory. Not sure why this would happen. Guess they have some goobs installing triggers and a few go flying...

You don't miss much brother.

Just pulled mine apart which ive been running with a sd3g trigger and it looks exactly loke that. Kind of makes me nervous.