Red Dot lost zero.

[tad1]

The gun was dirty vs super clean, the gun was held/rested differently while shooting.  The base/screws were a touch loose. Big temp difference from original sighting in. Variation between ammo of the same or different lots.  Choke tube is loose. Gun/ sight was bumped, jostled, vibrated.... 6" is not huge variance at 40 yards, I imagine the effective killing pattern is at least 20".  I would do what others recommend and shoot some birdshot again start at 20 yards move to 40 , then to tss and see what's up.  It seems a bit early to have Burris testing the site after you've shot only one shell at 40.... Yes, optics can fail, Dad just had a bad vortex riflescope replaced.  And I do agree with you, I hate to not feel confident in my equipment.  Keep us posted
    JT

[paboxcall]

My FF3 is mounted to the receiver, so when I disassemble to clean, I have a small Sharpie mark on the barrel lug that indexes with a small Sharpie dot on the tube. This way I know that barrel is torqued to the same amount each time I put it back together. Just eliminates another of those variables.

[Wigsplitter]

Always check the zero !! Every year!! Rifle or shotgun!! I can't understand why people don't do this every year other than maybe ammo cost BUT I'll gladly give $10 to know - gobblers are to hard to come by for me to throw a hope and a prayer at him!!

[RutnNStrutn]

I had the same thing happen on a Tru Glo green dot sight. It cost me one NC gobbler and almost a second one.
On the recommendation of a friend I swapped to Trijicon dual illumination RMR green dots, and haven't looked back. RMR stands for "rugged miniature reflex" and that's very fitting. In 8 years of using them on 2 scatterguns, they have NEVER lost their zero.