I'm just curious to know if this is normal.  After shooting this weekend, approx 80 rds, I noticed a lot of play between the receiver and the stock that I had not seen before.  I know this can adversely affect accuracy, but is it just endemic to the design and nothing to be concerned about?

A little bit of play won't be that big a deal to accuracy.  If it was between the barrel and receiver, that would be a different story.

I don't buy that at all. That's why precision rifles are bedded to the stock. Any movement between the stock and action will reduce accuracy as the POI will shift from the POA the moment the round is fired.

That's why I said "not that big of a deal."  I didn't say zero effect.  I just don't think the average shooter is going to notice a difference.  If you're shooting huge distances as Camp Perry it would be a different story.

Does your stock have a rounded receiver cross bolt?

AUG's are not precision rifles. MSAR trying to cater to the precision drum beaters is half the reason
I want out of the MSAR. I wanted a 24 LMG and it will never happen with MSAR because of "harmonics"
That stock play don't mean anything other than a easier to push take down button. If you look down the receiver
end of a tight new MSAR stock you will see flash from the stock manufacturing process. Wether it was
left there intentionally for the tight fit or not I don't care. I smoothed mine out on my latest STG because
The bolt carrier roller rides there. Still accurate for it's intended role. These are not bench rest rifles.
Sorry for the rant but MSAR has bigger real problems to worry about.

After I shot mine a bit, I built up the surfaces at the front of the stock with J-B Weld, then filed to fit. Everything fits nice and tight but isn't hard to disassemble. Have shot it several times since and it seems to be remaining consistent.

Thanks.  Its a Gen4 with the square lock.