I saw a vid on Youtube about it, it pointed out that you can in a way test your connection to the host by firing a few shots and comparing that to how fast the bullet counter is refreshed. Obviously it's not something accurate, but i tested it and noticed that in real laggy matches there could be up to a one second delay with the bullet count dropping when shooting single shots in a slow pace. So basically you could get a rough estimate on how bad your connection will be by shooting a few rounds at the beginning.
I saw that video as well and have done this in many matches and it doesn't work for me. My shots register immediately but the match may still lag like crazy.
This is due to where the lag is in the connection, upload or download. They cause different forms of lag
Sometimes I'll turn around and run backwards and shoot my own team mates at the beginning of a match. we end up shooting each other. Of course we can't kill each other in core. just something I'll randomly do.