The Crosscheck Mechanism is a set of code placed into the game in order to prevent hackers from abusing the clip restriction on weapons and becoming immortal.
Fortoresse displays figures calculated in game to an infinite number of decimal places, and then displays health and clips to the player rounded upwards to zero decimal places. This is the reason why when the shelter perk is equipped and the user takes shots in succession, the damage taken is shown to be a set of zeros and then occasional ones. The reality is that the player is taking a extremely small amount of damage each shot, and the current HP is displayed as a zero decimal figure rounded upwards.
A face value parameter ("What I see" or client value) is the value of the HP, ammo or clips displayed on the window above your character. It is the set of parameters that decides what happens within your own physics engine. In the case of ammo, it decides whether your character is able to fire a bullet, whether valid or nullified.
An underlying parameter ("What you see" or server value) is the value of the HP, ammo or clips as calculated by the server, depending on your character's actions. These values are calculated regardless of modifications placed on the player's character, and count down as if the player has no modifications. These values decide if the player's actions will be registered by the server.
The crosscheck mechanism applies a set of physics to your character that follows what is normal (or what agrees with the server) to the game, regardless of any alterations, whether to maximum ammo, clip restrictions, or HP. The game compares the user's server parameters before registering the validity of an action within game. Even if an ammo hack is applied, if the player is somehow still firing their weapon (i.e. client value of bullets is greater than zero) even though the server value of the clips or ammo is zero, a conflict in physics occurs and the game completely nullifies the weapon (no longer causes damage and no longer is visible to other players). The bullets fired from the gun at this point are known as phantom bullets. The identifying factor within game that reveals a disabled weapon is that firing at the ground will produce a checkered pattern that is impossible to pass through, and is no easier to destroy than if the ground was completely solid.
Sometimes, the crosscheck mechanism can nullify a weapon even if the player is not hacking. This will only happen due to an occasional glitch with picking up dropped clips from the ground, and the number of face value clips increases by two instead of one, while the underlying number of clips increases by one. In this way, the user apparently is able to fire an extra clip of bullets at the enemy, but will not do any damage because their weapon is nullified.
A hacked primary weapon that has a face value greater than zero but an underlying value that is negative or zero will not be re-enabled until the player respawns.
The crosscheck only has a noticeable impact on the primary weaponry, because the underlying values of clips are defined, whereas the underlying values of clips on secondary weaponry is undefined because they cannot run out of ammo. If a hack is applied to secondary weaponry that causes the face value to increase to 9999, then the crosscheck will disable the weapon as there is no reload, causing the underlying value to never reset.
It is possible to break the indestructible blocks in the spawn point by firing phantom bullets into it. The player must develop a phantom clip by gaining 2 extra clips from the Ammunition Perk instead of the usual 1. This will cause the face and underlying values of the clips to differ by one. When the player has reached the last clip, the face value reads the number of bullets remaining in the gun, while the underlying value reads 0, resulting in phantom bullets.
To gain a phantom clip, the player must pick up an Ammunitions Drop just before the weapon finishes reloading. The time space the player has to perform this trick is determined by their ping. The weapon's clips on the client tick down by 1, however the perk adds 1 clip on top of what the client reads before the weapon finishes reloading. So, it reverts the clips back to the original number and adds 1 on top of that, resulting in an additional clip.