For those who are looking for more vanilla friendly and balanced experience, I have another mod scratch-made by me - SupremacyArms (https://www.nexusmods.com/gta4/mods/338).

SupremacyArms is a refined, polished and balanced version of the Realistic Weapon Overhaul mod, offering the same weapons as the vanilla GTA IV, but keeping the RWO's hardcore gameplay. This is ideal for those who love the overall concept of Realistic Weapon Overhaul, but don't want to go too far away from the vanilla IV.

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Realistic Weapon Overhaul is aimed at rebalancing the whole shooting experience so that every single weapon was worth shooting and there were no bad and good weapons. Every weapon now is good in its own way, and the gameplay is WAY harder, so keep that in mind. The mod is made using various other mods so if you want to download them separately, all links and credits are attached.

Changelog:
Damage increased
Bullet spread adjusted (for shotguns only, for bullet spread for other weapons see Recommended mods in the readme file)
Effective range increased
Number of rounds picked up on the street adjusted
Max. number of ammo carried adjusted
Physics force increased (how much peds are kicked when hit)
Clip size adjusted
Shot echo increased
RPG rocket speed increased
*Parameters above are adjusted based on real-life ammo power, caliber, barrel length, mag capacity, ammo weight etc, in some cases I set the parameters based on real life shooting videos from YouTube xD

The only thing that is totally mine is weaponinfo.xml, I made it specifically for the weapons included in the mod:
- Weapon set 1:
Desert Eagle > .44 Automag (.44)
Remington model 1100 (12 gauge)
MP5 > FN P90 (5.7x28)
M4 > MG36 (5.56x45)
Advanced Sniper Rifle > DSR-1 (.308)
RPG
Grenade (unchanged)
- Weapon set 2:
Glock 17 (9x19)
Pump Shotgun > Street Sweeper (Armsel Striker, 12 gauge)
Micro Uzi > IMI Uzi (9x19)
AK (7.62x39)
M40a1 (7.62x51)
RPG
Molotov (unchanged)