You are correct, that is perfectly normal. The upper and lower are held together by two pins, and there will be some space between... enough for light to pass through just as you are seeing with your rifle.Disregard, after doing research I discovered that this is normal.
Next time I will research before posting prematurely.
I was about to suggest the same but I use blue painters tape. I put two layers on and trimmed it with an x-acto knife (actually, a scalpel but they are hard to find) and now it's crazy solid.Install an Accu-wedge or put electrical tape along the mating surfaces to snug it up.
Hold your rifle up to the light... I guarantee that you will see light between the upper and the lower. These rifles are held together by two pins and they are not hand fitted.I agree with ditto1958. One of the reasons I bought the AR-556 was because there was no slop. I can see it on a gun that has been fired a lot but not on a new one.
If you get the light, the area where the two pieces come together, and your eyes all in alignment, you will see quite a bit of light come through. And when you take a photo with bright light coming towards the camera, you will tend to get some over exposure.I went and checked mine after this post, I did find a hint of light poking through but nothing like to OP has. I feel mine is pretty tight, going to do some shooting in a week or so with a couple friends, one has an M&P 15 NOE Magpul Spec series, the other a CMMG lower, BCM Upper, I'll be examining these closer.
Tolerance can go that way as well... How many rounds do you have through it? My S&W was tight where I had to use a punch to remove the rear pin. It loosened up enough that I can push it out with my finger after a few hundred rounds.Mine is very tight ???
Ditto, there is no way that there is no light passing in-between your upper and lower. You just are not looking at it right... And it isn't as big of a gap as it looks in the OPs pic. I can't even get a piece of paper through mine, but I can see light, and I can see through it. Mine also lock up tight and do not have movement.1. Mine is tight, with no light showing through. Other AR-556's I've handled in stores have been the same.