Here is a list of the designs behind the things in UZF.
Most of the 5.7 mm guns were inspired by FN guns (e.g. FN Minimi, Five-seveN...) The idea is that Medeiga Tech produces 5.7 mm as standard ammunition, i.e. "economical ammo" (or "throw away rounds" as the UDC calls them). The Medeiga 4 is actually inspired by Vincent Valentine's gun "Cerberus" from Final Fantasy VII and is chambered for 5.7 mm specifically because it's more abundant.
The BR7 was inspired by the FN P90 (primarily), M4 and AK47.
The sniper rifles aren't inspired by anything specific. Their calibers are chosen to fill their positions. Serene's more of a support rifle (note clip size and it's semi auto). The Sincere is basically a "anti-everything" rifle (designed to destroy whatever you're shooting at). The Medeiga 4's purpose is for combat sniping (i.e. aiming quickly and shooting). Although the Medeiga 4 is the least accurate sniper rifle (due to terminal ballistics from the rounds used) it's the most effective because it trades accuracy for firing rate, which typically increases hit rate (this is the principle that lead to the machine gun becoming the primary tool of war). The 5.7 mm "throw away" ammo facilitates this. It also deals more damage per trigger pull since it's firing 4 rounds simultaneously.
The shotgun was inspired by the Saiga-12. Not many options here to make it more interesting.
The MC5 takes inspiration from the MP5 and MAC-10 but is chambered for "throw away" rounds. Its purpose is to spray bullets at the target (obviously).
The Medeiga 6 takes inspiration from the Mateba Model 6 Unica.
Notice that any deviation from the 5.7 mm rounds show a clearly more powerful round chosen for specific properties (some calibers are used for hunting, others sniping, etc).
The damage system uses line intersection calculations to determine how much damage a weapon does against a target. Geometry besides line intersection can be used as well (e.g. vector projection). We should be sure to encapsulate this feature so that we can figure out the geometric calculations later, which will probably be faster than line intersect calculations (since it may not require branching). For now, line intersection calculations are easier.
If a bullet hits within 25% width from the target's center, then body armor protection kicks in (how much depends on the body armor). We could say 50% damage to start with.
The damage a bullet deals depends on how close to the center of the target it hits. At the center it deals 100%. At the edge of the target it deals 50%. Damage scales linearly. Example: At 25% width from the target's center, damage is 75%.
Radial blast damage drops by distance squared. Only units that are within the blast radius are affected by this. Blast radius is defined as the square root of the damage. This means that it must deal at least 1 damage to the unit (or it doesn't count). Example: A grenade that does 400 damage means any units that are 20 (pixels) away from the blast will be ignored, while damage will be calculated for those within the blast radius.
Directional blast damage will require more complex calculations. It can be achieved by defining an elipse and rotating target coordinates before checking them but maybe there is a more efficient way of doing it.
Any targets that are lit on fire will continue to take residual damage. Residual damage is directly proportional to how much of the target was flamed. If 30% of the target's width was flamed, then the target takes 30% of the flame's damage per second as residual.
Melee weapons deal maximum damage at all times.
The algorithms used when calculating various things try to balance realism and speed (CPU). Although speed weighs more than realism, we hope to be able to put a lot of detail (realism) into the game with minimal CPU cost. Since the game's 2D this should be easier than doing the same with 3D (which would be more time consuming, both by development and CPU). Also, since it's 2D, expectations (for realism) will typically be less by the average player which gives us (developers) more flexibility in our schedule.
Although realism is desired, what counts more is anything that makes the game over the top (i.e. "awesome"). Logic will be broken (at times) if it may make the game more interesting (in a good way).