I asked him to check the protrusion in case it was obviously short. You dont need a gauge for that. Considering he didnt have another bcg at the moment to swap out parts, it is a reasonable thing to check.
Having said that, the advice to find another bcg to change out parts; one at a time, is your best bet.
The tail on that bolt does look funny. Is it angled?
If you cannot come up with another bcg quick let me know and i will hook you up for troubleshooting purposes.

