It shoots further at full damage. Has less recoil. Shoots faster. Penetrates better and is lighter so you move faster.

Vanilla Custom
Weapon Pistol G19 (Pistol)
Tier 1 1
Mag Size 15 15
Total Ammo * *
Damage 36 36
Damage/Bullet 36 36
Damage/Mag 540 540
Damage/Sec 205.80 216.00
Total Damage
Rate of Fire 343 360
Cycle Time (ROF/s) 0.1749 0.1667
Vertical Punch 2.000 1.675
Spread/Shot 1.00 0.56
Max Spread 30.00 30.15
Spread Decay 5.00 2.99
Min Crouching Spread 0.50 0.80
Min Standing Spread 1.50 1.01
Min Airborne Spread 3.00 1.81
Max Moving Spread 3.00 3.62
Max Player Speed 250 264
Max Range 2500 5250
Effective Range 2625
Range Modifier 0.750 0.936118
Penetration Layers 2 2
Penetration Power 30 31
Penetration Distance 0 0
Char Penetration Dist 768
Projectiles/Shot 1 1
Weight 10 5

There's barely a difference