"Each player starts with the same basic pistol. Every time you kill an enemy with your gun, you're upgraded to the next weapon. Anyone killed with a melee attack is demoted to the previous weapon, so watch your flank. Suicides also set you back to the previous tier, most often occurring when using explosive weapons. The match ends when someone cycles through all twenty weapons. Success in Gun Game requires aggressive tactics and familiarity with each weapon in the rotation. Don't worry about dying - just go for a lot of successive kills. "
The game consists of six players competing in a free-for-all-style game. As players get more kills, the player will receive different weapons. However, melee kills do not advance the killer to a new weapon, but demote players to their previous weapon tier instead. The first person to achieve a kill with all twenty (or 18 in MW3 and Ghosts; 24 in Advanced Warfare) weapon tiers wins. However, if the match ends without anyone getting a kill with all the weapons, the player on the highest weapon tier wins the match. Due to the fact that only 20, 24 or 18 kills are needed to win, and the game is a Free For All, games are usually fairly short.
Direct suicides with a weapon will result in a demotion. By definition, this means being caught in the blast of an explosive weapon's splash damage. Suicides by car bombs or red barrels will also demote the player, but suicide by fall damage will not except in Black Ops II.
Also, getting double kills will not advanced the player by two weapon tiers; only one (except in Call of Duty: Advanced Warfare).
If the player kills someone else by blowing up a car with a launcher, they don't advance to the next tier.
If the player kills someone with a launcher and then kills themselves, they will go back one tier. However, if the enemy damaged the player before they killed themselves, the other player will get an "Assisted Suicide" kill, but will not advance.
Kills from the grave (afterlife kills) will advance the player a tier.
David Vonderhaar, the design director for Treyarch, states that the idea for this game mode came "straight from the community," which was a thread created on their own Community Forums. Gun Game had an overwhelming demand from the majority of the community.
In Ghosts, the first sixteen weapons are randomized within their class, with random attachments. The player can view their current weapon and attachments by selecting Change Class in the menu. However, the assault rifle at thirteen will always have no attachments and the shotgun at fourteen will always have the Slug Rounds attachment in conjunction with a Red Dot Sight.
Gun Game seemed to have been planned to be released as a game mode in Call of Duty: Advanced Warfare, as in one issue of Newsweek Magazine, it was included with a list of game modes in Advanced Warfare; in addition, audio files for the initial start-up exist. Gun Game was later added to the game on February 13th, 2015.
As of an update, Gun Game now uses different weapon variants of different guns instead of the default guns.