Would be a great upper receiver for a lightweight build but was machined wrong - TRYBE Defense AR-15 Ultra Lightweight Magnite Stripped Upper Receiver

I had no issue with optics planet it was the manufacturer tribe defense that let a bad part go through their QC and ship to their customer. The receiver has a 3/8 inch gap where the receiver butts up to the lower by the buffer tube I have sent three emails to try defense telling them that I would like to exchange if it's just this one that was machine wrong but if it's made that way then I will have to return because it hasn't fit on three different lowers I have paired with it I have not got a response back from tribe probably going to just send back to optics planet and get a CMMG I explained to tribe I was trying to build an AR-15 with as many tribe defense parts as I could I have the one to eight LPVO that I love the magnite charging handle the tribe handguard and the tribe low mass bolt carrier and wanted to use the tribe go fast lightweight upper receiver but I am almost positive this one receiver was machine wrong but I cannot get tribe to send me an overall length measurement of the upper receiver so I can measure and double check before I send mine back to exchange for another one and have the same issue