Gun Master is a fun game mode but there will always be players that advance faster than others and rounds do not last very long.
Frustration levels get high when you cannot get a kill with a certain weapon for so long and players are known for leaving when they keep getting killed/cannot get kills/demoted to their last weapon when killed by a knife.
I am all up for testing it on the event server when possible but as a main server/takeover from Metro, I feel that that specific gamemode is not one that will help keep the server as active and as full as we need it to be, but with trial runs and correct settings then it may be possible.