Ok, a couple of years ago, I purchased a Mega upper from another member who had accidently squeezed it while removing the barrel...  apparently he didn't have an action clamp so he was using blocks of wood to clamp it in a vise.... I've inserteed a BCG, and it is snug near the back of the ejection port, would it be safe to use this for a build, or is it nothing more than an inexpensive paper weight?

Thanks, Dan

I assume this guy clamped the receiver side to side instead of top to bottom?   If that's the case, I'd try spreading the receiver at the snug spot to see if you can move the sides enough to allow the BCG to move freely.  It might work, and if it doesn't, you're no worse off than with it too tight.