Give us some details on the parts used as many are not interchangeable between platforms. Take some close up pics of the bolt locked back, inside the ejection port with loaded mag installed, inside the upper looking at feed ramps, upper and lower fit up etc. the more and detailed the photos the better. What’s going on with the front pin in that pic? Is is fully inserted? Looks off but maybe because of the angle. Have you ever built an ar before? Is it doing this cycling with the charging handle only or does it also do it releasing the bolt from the locked back position with the bolt release? Are you sure the mag was fully seated? What caliber?