So this seemed to generate lots of controversy. To those who wondered or offered various comments...
We sent the OP a return shipping label and received the rifle back. With about three quick whacks by hand, the rifle opened up. It was certainly tighter than most, but it was apart within seconds of having it out of the box. While it would have become easier to open over time and use, or maybe with some oil to help it along when new, we replaced the upper receiver with one that was less snug of a fit, and returned the rifle today.
Take away, the STAG-10 upper to lower fit is usually tighter than an AR15s. If your rifle is tight out of the box, remember, it went together by hand, and it will come apart by hand. You won't break it by giving it a good solid wrap. As the rifle is used and the anodizing smooths out, it will become less tight.
Also, before sending the rifle back the OP was contacted by AEI as well as the service manager at Stag Arms. Purchasing a factory rifle imported by the Arms East through your favourite local gun shop gets you full support, including shipping, from Arms East and Stag Arms, should you need it, for life.
We hope all is smooth from here in and the OP is happy with the rifle going forward.