Weapons:

Complete the indicated task to unlock the corresponding weapon bonuses.

Bolt Action Rifles
Springfield: Reach level 4.
Sniper Scope: Already available (increases accuracy and range).
Bayonet: Complete Marksman Challenge 1 (increases melee attack range).
Rifle Grenade: Complete Marksman Challenge 2 (grenade launcher attachment, replaces Perk 1 slot).
Arisaka: Reach level 4.
Sniper Scope: Complete Marksman Challenge 1 (increases accuracy and range).
Bayonet: Complete Marksman Challenge 2 (increases melee attack range).
Rifle Grenade: Complete Marksman Challenge 3 (grenade launcher attachment, replaces Perk 1 slot).
Mosin-Nagant: Reach level 21.
Sniper Scope: Complete Marksman Challenge 1 (increases accuracy and range).
Bayonet: Complete Marksman Challenge 2 (increases melee attack range).
Rifle Grenade: Complete Marksman Challenge 3 (grenade launcher attachment, replaces Perk 1 slot).
Kar98k: Reach level 41.
Sniper Scope: Complete Marksman Challenge 1 (increases accuracy and range).
Bayonet: Complete Marksman Challenge 2 (increases melee attack range).
Rifle Grenade: Complete Marksman Challenge 3 (grenade launcher attachment, replaces Perk 1 slot).
PTRS-41: Reach level 57.

Rifles
SVT-40: Reach level 4.
Flash Hider: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Telescopic Sight: Complete Marksman Challenge 3 (enhanced telescopic sight).
Gewehr 43: Reach level 7.
Suppressor: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Telescopic Sight: Complete Marksman Challenge 3 (enhanced telescopic sight).
Rifle Grenade: Complete Marksman Challenge 4 (grenade launcher attachment, replaces Perk 1 slot).
M1 Garand: Reach level 17.
Flash Hider: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Bayonet: Complete Marksman Challenge 2 (increases melee attack range).
Sniper Scope: Complete Marksman Challenge 3 (increases accuracy and range).
Rifle Grenade: Complete Marksman Challenge 4 (grenade launcher attachment, replaces Perk 1 slot).
STG-44: Reach level 37.
Flash Hider: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Telescopic Sight: Complete Marksman Challenge 3 (enhanced telescopic sight).
M1A1 Carbine Reach level 65.
Flash Hider: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Bayonet: Complete Marksman Challenge 3 (increases melee attack range).

Sub Machine Guns
Thompson: Reach level 4.
Suppressor: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Round Drum: Complete Marksman Challenge 3 (increased ammunition capacity).
MP40: Reach level 10
Suppressor: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Dual Magazine: Complete Marksman Challenge 3 (increased ammunition capacity).
Type 100: Reach level 25.
Suppressor: Complete Marksman Challenge 1 (invisible on radar when firing, reduced muzzle flash, but shorter range).
Aperture Sight: Complete Marksman Challenge 2 (precision sight).
Box Magazine: Complete Marksman Challenge 3 (increases ammunition capacity).
Ppsh: Reach level 41.
Aperture Sight: Complete Marksman Challenge 1 (precision sight).
Round Drum: Complete Marksman Challenge 2 (increased ammunition capacity).

Shotguns
M1897 Trench Gun: Reach level 4.
Grip: Complete Marksman Challenge 1 (vertical foregrip to reduce recoil, replaces Perk slot 1).
Bayonet: Complete Marksman Challenge 2 (increases melee attack range).
Double Barreled Shotgun: Reach level 29.
Grip: Complete Marksman Challenge 1 (vertical foregrip to reduce recoil, replaces Perk slot 1).
Sawed-Off Shotgun: Increases weapon spread, but reduces accuracy.

Machine Guns
Type 99: Reach level 4.
Bipod: Complete Marksman Challenge 1 (reduces motion for more accuracy).
Bayonet: Complete Marksman Challenge 2 (increases melee attack range).
BAR: Reach level 4.
Bipod: Complete Marksman Challenge 1 (reduces motion for more accuracy).
DP-28: Reach level 13.
Bipod: Complete Marksman Challenge 1 (reduces motion for more accuracy).
MG 42: Reach level 33.
Bipod: Complete Marksman Challenge 1 (reduces motion for more accuracy).
FG 42: Reach level 45.
Bipod: Complete Marksman Challenge 1 (reduces motion for more accuracy).
Telescopic Sight: Complete Marksman Challenge 2 (enhanced telescopic sight).
Browning M1919: Reach level 61.
Bipod: Complete Marksman Challenge 1 (reduces motion for more accuracy).

Pistols
Colt M1911: Reach level 4.
Nambu: Reach level 4.
Walther P38: Reach level 4.
Tokrev TT-33: Reach level 21.
.357 Magnum: Reach level 49.

Primary Grenades
Frag: Reach level 4.
N 74 ST: Reach level 4.
Molotov Cocktail: Reach level 10

Special Grenades
Smoke: Reach level 4.
Tabun Gas: Reach level 4.
Signal Flare: Reach level 4.