Longevity, Accuracy Tips for the AR15

[customcutter]

It's threads like this one that makes the price of admission worth being here. Thanks guys for all the advise.

Lacking an Upper Rec. Lapping Tool what is a good way measure or visually inspect to verify if the Receiver's face is true?

I agree it's worth twice the price of admission.

FYI, I did see one thread on AR accuracy where the builder used a surface plate and machinist square to check the top of the upper for squareness to the face of the threads. I really don't consider that an accurate way of measurement, what about the other 359* of the circle? Only way I can think of would be to use the lapping tool and lap it in.