A few weekends ago, my wife had a Romeo 3 Max lose zero, and mess up her match. With ammo so tight, we haven’t done as much zero verification shooting with our match guns. My wife ordered this inexpensive boresighter from Amazon, and has been using it to confirm zero on her CO Legions, and so far it seems to be working. Today, I needed to zero a newly installed optic on a CORE, and she used the boresighter to get the zero close before we left home. Here is a link:
https://www.amazon.com/MidTen-Sight-.../dp/B07GGWJSJ6
These are my first shots at 20 yards, using only the zero from the boresighter.