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I was in a low light class last night; the first I've done with the AUG.  I kept seeing a small red flash in the corner of my eye with each shot.  It looked like it was coming from the ejection port.  
I asked people if they saw it, and none did.  However, with the angles involved with where we stood as the shooter worked through the scenarios, that area would have been blocked from view most of the time.  

It was there, whether anyone else saw it or not.  It is possible it was a reflection off my glasses and/or red dot lens and was coming from somewhere other than the port.
Anyone else ever see this?  

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Gas port flash.

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I finally thought about that, but of course I never noticed it again after that point.
It seemed farther back, but maybe it wasn't.

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Flash from the ejection port isn't uncommon with semi-auto rifles, depending on the ammo.  Most likely just the ejection port flash though.  HK416's have a Venturi on their gas dump port that mitigates most of the flash.  The AUG just has a hole sticking out of the side of the piston chamber.  That's why it's also a harder rifle to suppress well.