Marksman (Challenges)

Call of Duty 4: Modern Warfare Challenges
Marksman's Challenges are weapons challenges that unlock the Red Dot Sight, Silencer, ACOG Scope, and Foregrip (for LMGs and Shotguns) attachments. They require X amount of kills to unlock these attachments. The first challenge for Assault Rifles and SMGs requires 25 kills, which unlocks the Red Dot Sight. The second challenge requires 75 kills, and unlocks the Silencer. The third and final challenge requires 150 kills, and unlocks the ACOG Scope. Shotguns and Sniper Rifles have different attachments and kills required compared to Assault Rifles, LMGs, and SMGs. LMGs unlock Red Dot Sights after 25 kills, Foregrip after 75 kills, and ACOG after 150 kills,but basically it's the same process. Shotguns unlock the Red Dot Sight after 25 kills, and Foregrip after 50 kills. Sniper Rifles just unlock the ACOG Scope after 100 kills. These, along with Expert Challenges are required to unlock Golden weapons. Note that the MP44 is the only gun that does NOT have a Marksman Challenge, it only has an Expert Challenge, which is still required for the Golden AK-47.

Items unlocked after 25 kills (Awards 50 XP, Marksman I)
 * Assault and SMGs - Red Dot Sight
 * LMGs - Red Dot Sight
 * Shotguns - Red Dot Sight

Items unlocked after 50 kills (Awards 500 XP, Marksman II)
 * Shotguns - Foregrip

Items unlocked after 75 kills (Awards 500 XP, Marksman II)
 * Assault and SMGs -Silencer
 * LMGs - Foregrip

Items unlocked after 100 kills (Awards 500 XP, Marksman I, only Marksman challenge for sniper rifles)
 * Sniper Rifles - ACOG scope

Items unlocked after 150 kills (Awards 1000 XP for completing Marksman III)
 * Assault and SMGs - ACOG scope
 * LMGs - ACOG scope

Call of Duty: World at War Challenges
The Marksman Challenges in Call of Duty: World at War have only the slightest differences compared to Call of Duty 4. For example, the Marksman I challenge can be completed with 25 kills with the weapon you have used to complete the challenge, this would unlock things such as an Aperture Sight or a Round Drum. Every weapon in World at War has unlockables for it except the PTRS-41. Though there is a Killer challenge called "Pistol Marksman," there are no unlockable attachments for pistols.

The unlockables for WaW weapons are the following:

Assault rifles

 * 25 kills: Suppressor and 100 XP
 * 75 kills: Aperture sight and 500 XP (Bayonet for M1 Garand)
 * 100 kills: Telescopic sight and 750 XP (Rifle Grenade for M1 Garand)
 * 150 kills: Rifle Grenade and 1000 XP (Double magazine for M1A1, Sniper scope for M1 Garand, no challenge for SVT-40, no challenge for StG 44)

Sub Machine Guns

 * 25 kills: Suppressor and 100 XP (not for PPsh-41)
 * 75 kills: Aperture sight and 500 XP
 * 150 kills: Double Magazines and 1000 XP

Machine Guns

 * 25 kills: Bipod and 100 XP
 * 75 kills: Bayonet (only for Type 99), Telescopic Sight (only for FG-42) and 500 XP for these two weapons

Shotguns

 * 25 kills: Bayonet (M1897 Trench Gun), Grip (Double-barrelled shotgun) and 100 XP
 * 50 kills: Grip (M1897 Trench Gun), Sawed off (Double-barrelled shotgun) and 500 XP

Bolt action rifles

 * 25 kills: Sniper scope and 100 XP (no unlockable for Springfield)
 * 75 kills: Bayonet and 500 XP
 * 150 kills: Rifle grenade and 1000 XP
 * Please note that the PTRS-41 does not have marksman challenges.

Assault rifles

 * 10 kills: M203
 * 25 kills: Red Dot Sight
 * 75 kills: Silencer
 * 150 kills: ACOG Scope
 * 300 kills: FMJ


 * Additional attachments


 * Masterkey Shotgun - 20 kills with the Grenade Launcher
 * Holographic Sight - 60 kills while looking through the Red Dot Sight
 * Heartbeat Sensor - 15 kills with the Silencer attachted
 * Thermal Scope - 20 kills while looking through the ACOG Scope
 * Extended Magazines - 40 bullet penetration kills with FMJ attached

Submachine guns

 * 10 kills: Rapid Fire
 * 25 kills: Red Dot Sight
 * 75 kills: Silencer
 * 150 kills: ACOG Scope
 * 300 kills: FMJ


 * Additional attachments


 * Akimbo - 20 kills with Rapid Fire attached
 * Holographic Sight - 60 kills while looking through the Red Dot Sight
 * Thermal Scope - 20 kills while looking through the ACOG Scope
 * Extended Magazines - 40 bullet penetration kills with FMJ attached

Light Machine Guns

 * 10 kills: Grip
 * 25 kills: Red Dot Sight
 * 75 kills: Silencer
 * 150 kills: ACOG Scope
 * 300 kills: FMJ


 * Additional attachments


 * Holographic Sight - 60 kills while looking through the Red Dot Sight
 * Heartbeat Sensor - 15 kills with the Silencer attachted
 * Thermal Scope - 20 kills while looking through the ACOG Scope
 * Extended Magazines - 40 bullet penetration kills with FMJ attached

Sniper rifles

 * 10 kills: Silencer
 * 25 kills: ACOG Scope
 * 75 kills: FMJ


 * Additional attachments


 * Heartbeat Sensor - 15 kills with the Silencer attached
 * Thermal Scope - 20 kills while looking through the ACOG Scope
 * Extended Magazines - 40 bullet penetration kills with FMJ attached

Machine Pistols

 * 10 kills: Red Dot Sight
 * 25 kills: Silencer
 * 50 kills: FMJ
 * 75 kills: Akimbo
 * 100 kills: Holographic Sight
 * 150 kills: Extended Magazines

Shotguns
For all except Ranger and 1887:
 * 10 kills: Red Dot Sight
 * 25 kills: Silencer
 * 75 kills: Grip
 * 150 kills: FMJ
 * 150 kills: Holographic Sight
 * 400 kills: Extended Magazines

For Ranger and 1887:
 * 10 kills: Akimbo
 * 50 kills: FMJ

Handguns

 * 10 kills: FMJ
 * 50 kills: Akimbo
 * 75 kills: Tactical Knife

.44 Magnum and Desert Eagle only

 * 100 kills: Tactical Knife

M9 and USP Only

 * 25 kills: Silencer
 * 150 kills: Extended Magazines