Originally Posted by CrippledPidgeon
Your issue is in the full length guide rod. It may not have enough clearance around the plug to allow the rod to rotate enough to clear the bottom barrel lugs. In this case, yes, you'll have to use the GI method of depressing the plug and rotating the bushing to pull the plug out the front.
That explains exactly what it happening. I guess I will have to get much more practiced at assembling it. The spring is 18.5 lbs. I think, so not depressing easily with just a thumb! Plus the plug edge really cuts into your thumb, even leaving a severe imprint on my thumb through leather gloves.