This page will help you learn understand the bullet mechanics in Phantom Forces, which are currently more advanced than most other Roblox FPS games at the moment. There are currently 5 types of mechanics that affect where your bullets land after they've been fired.
First and foremost, the game has a thing called "Bullet Drop". It is a value that affects how fast the bullets of a gun fall in altitude due to gravity(along with a velocity decrease) at longer ranges. In simpler terms, it means at longer ranges (etc. 1000 studs) you will need to aim above your actual opponent to be able to land shots(and headshots) on your opponents at long range. In-game, the bullet drop level is 160 SDPS or (Stud Drop Off Per Second Variable). In regular Roblox games, the gravity is 196.2. 196.2 - 160 = 36.2. So there is only a 36.2 Difference in Gravity of Bullet Drop and Normal Roblox Gravity.
Accuracy is the accuracy of your shots, and the term for this in many other games is "Cone Of Fire." Although this is a weapon statistic, not a direct part of the bullet like Bullet Drop is, it is a mechanic that very much affects where your bullet lands. If you have a weapon that has 100% Accuracy, a shot will always go straight down the center of your screen, provided you aren't moving yourself or your weapon. If you have a low Accuracy statistic, the gun will probably land many of its shots to the left or right of your screen's center, rather than the actual center. As you might expect, a rifle like the starter Intervention will be significantly more accurate than a PDW like the P90.
Stability is the stability or recoil of your shots. This could be termed "Controllability." Although, like Accuracy, this is a weapon statistic which doesn't affect the bullet in-flight, it does affect your aim. There are two types of this stat, "Hip Stability" and "Aim Stability." The latter, as you can guess, affects your weapon while you're ADS'ing, and the former should be self-explanatory. This is not merely a measure of recoil per shot, taking into account the ROF of the weapon in question as well as how much the weapon sways when hipfiring/ADSing. The AS VAL, for example, has low recoil per shot, but it fires so fast that the weapon may point itself above your target if you don't pay attention, which is why it doesn't have a very good Aim Stability statistic. Meanwhile, the G36 has a low-ish recoil per shot, but the weapon sways much more hipfiring than ADS'ing. If you have around 75% Stability, you will have low gun rise and sway while firing that weapon for extended periods of time. If you have 0 Stability though, your gun will flail around making it difficult for recoil control and a lower chance of hitting your target.
Velocity is the speed of your bullets, and only becomes really important to your aiming at mid-long ranges. The faster a bullet flies, the less a player will have to "lead" a moving opponent by keeping the mouse target a short distance ahead of the moving target. Normally players will find oneself leading targets on the horizontal axis, although a shooter above his/her targets may need to compensate with vertical distance as well. Although Bullet Velocity is its own variable, it's also a factor in the aforementioned Bullet Drop. If you shoot at a 1000 studs (the Roblox distance unit) and your gun has the velocity of 2500 studs per second, the gun bullet will reach the opponent in about 0.4 seconds, which is why it's necessary to compensate with distance between one's sight reticle and the actual target.
Spread (Shotguns Only)
Unlike normal rifles and the like, shotguns fire pellets. Spread is a mechanism for shotguns where if there's higher spread, the pellets of the shot go further apart, the further away one is from a target. Shotgun spread is the way shotguns like the quick-firing KSG-12 are kept in balance with the usual assault rifles and PDW Class weapons, because each individual pellet of a shotgun doesn't do that much damage on its own. It may be related to the shotgun's Accuracy statistics (cone of fire), but this is unconfirmed. The spread of shotguns decrease when ADS'ing and Hipfiring. Unlike the other bullet mechanism, spread becomes random and unpredictable every time you fire the gun, so you it is possible that you could get a hitmarker in point blank range or a 100 stud insta-kill.