Check me on this logic path. If it Closes on: GO gauge -if it closes, it is safe NO-GO- it is not a new rifle, but not necessarily "unsafe" Field- if it closes, it is not safe. If above is correct, and I want to minimize buying parts, and I want to check sharing BCG between ARs, I could just buy one- either the Go or Field gauge. Why need more than one? Why is one better than the other? Why need a set?