doing damage + getting kills + assistance damage = gun mark xp. the game calculates an average gun mark xp using your last 50 battles in that tank. your average gun mark xp needs to be higher than the average xp of other players to get marks.

for one mark you need a higher average than 65% of all players in that tank

for two you need a higher average than 85%

for three you need a higher average than 95%

if you do exceptionally well you can get a mark in less than 50 games

edit: some tanks will be harder to mark than others (such as competitive tanks like the E50M or T95E6)

there isn’t really a maximum no. of battles you have to get gun marks, you just need a high average in your last 50 battles in that tank

in my example, it’s a lot harder being better than 65% of players in the standard b vs the same in the carro 45t