(adsbygoogle = window.adsbygoogle || []).push({}); So how dose ppl do it bcoz custom zombies don't go to leaderboads

Have you and your friend sign on a guest account using a 2nd controller and sign out the guest account when the countdown hits 1 (Game Starting: 4 3 2 1)
For 3 people. Only 1 person needs to do this.

Ok sweet mate

Or, how I've always done it, was just get my party together (say, three of us) then go to public match, assuming we get a fresh lobby, we all ready up and the game starts up with just us. That obviously isnt full proof but I've never had a random join in during the match countdown or anything.

On Public Match. Just press the "ready up" button as fast as possible so that the game would start already. If someone joins, back out then retry.