The Upgrades:
Path 1:
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MP5/10 ($300 in-game cash):10mm version shoots further and hits harder.
SCAR-H ($750): Special Forces Assault Rifle heavy variant provides crowd control capability to a single well-positioned soldier.
M60 ($1500): Belt fed 7.62 machine gun increases damage and range.
Browning ($3000): Freehand .50 caliber heavy machine gun eviscerates zombies and looks commando doing it.
M41-A Grendel ($14000, must unlock first for 300 SAS dollars.): 12.7mm full auto caseless destructive savagery.
Path 2:
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Stopping power ($250 in-game cash): fast burn propellant hits harder and does more damage
Steady Aim ($250): ported barrels and muzzle brakes increase effective range
Juggernaut ($500): Prototype exoframe nearly doubles direct contact survivability.
Stimpack ($1500): Adrenaline and painkillers effectively make damage disappear over time.