Yeah I see your point, TP. You wouldn't expect the Spikes lower to be out of spec, they sell a ton of them and I've never heard of a problem in that area. But then Magpul knows their stuff too. Still, I'd suspect the problem to be plastic instead of metal, though.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
You'll remember the quality of a gun long after you forget how much you paid for it.
US Army 1966-69, VFW Life Member, Retired Geek