Vertical line on upper receiver
This may seem silly to some but my curiosity is killing me. On the left side of all cast and forged uppers ( that I have seen )there is an embossment that coincides with the recess were the cam pin is when the BCG is closed. On that embossment on the outside of the receiver there is a .250 vertical line. Does anyone know the purpose or meaning of this line. I cant seem to find an answer with the search function. And like I said its just bugging the dog crap out of me. Everything else on this gun has function and meaning....except this little line. I'm getting close to losing sleep on this one. I sometimes will fixate and obsess over something like this. Right now it's just fixation. Please help me !
Thanks in advance.
Vince