bought an m4 upper a few months back.

been working on it for refinishing. had a couple small gouges in the aluminum on the left side and tons of tiny nicks. this would be in the area that the bolt travels through, closer to the rear than the front.

i filled the surface imperfections with JB weld and leveled the surface and 0000 stell wool, using very fine sandpaper so as not to take off much aluminum.

should i have safety concersn here?

This is the inside of the upper receiver where the bolt CARRIER cycles rearward and forward when fired? Can you determine from the shape of the gouges/dings if they are from rearward or forward movement of the bolt carrier? Big question is: Who made the upper and with whose parts (ASA or Hesse)? The short answer is: NO, the parts should cycle without tearing each other up. The standard answer is also to take it back to the source and demand that it be fixed/replaced/refunded.

the receiver is a colt. i bought it knowing it was beat up, so no issue with the seller.

the gouges are not very deep and are on the outside of the receiver, but along the side where underneath the carrier moves. probably caused by dropping it onto something hard.

sorry if i wasn;t clear at first.  

As long as you don't detect the outside dent making any change to the inside surface, it's only cosmetic. Besides, it adds character and appears to others that you have thousands of rounds of experience. No functional problem at all. Shoot and enjoy.

that's the answer i was hoping for.

[:D]

i started to suspect it after seeing other posts about cutting holes for side charging handles.

thanks for checking back and providing the info.