In Escape from Tarkov the handling of weapons can be trained through active use. In short, the more you use a certain weapon, the more skilled you become with it.
Depending on the weapon, reaching level 2 or level 3 will provide new reload animations. Level 3 grants the ability to reload while aiming down sights for all weapons.
Variants of a weapon family share the same mastery. You can see which guns are connected and how much EXP each level requires below.
Assault rifles/LMGs
Required EXP for level 2: 1500
Required EXP for level 3: 3000
Kalashnikov AK-101 5.56x45 assault rifle
Kalashnikov AK-102 5.56x45 assault rifle
Kalashnikov AK-103 7.62x39 assault rifle
Kalashnikov AK-104 7.62x39 assault rifle
Kalashnikov AK-105 5.45x39 assault rifle
Kalashnikov AK-74 5.45x39 assault rifle
Kalashnikov AK-74M 5.45x39 assault rifle
Kalashnikov AK-74N 5.45x39 assault rifle
Kalashnikov AKS-74 5.45x39 assault rifle
Kalashnikov AKS-74N 5.45x39 assault rifle
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Kalashnikov AKM 7.62x39 assault rifle
Kalashnikov AKMN 7.62x39 assault rifle
Kalashnikov AKMS 7.62x39 assault rifle
Kalashnikov AKMSN 7.62x39 assault rifle
Molot Arms VPO-209 .366 TKM carbine
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Kalashnikov AKS-74U 5.45x39 assault rifle
Kalashnikov AKS-74UB 5.45x39 assault rifle
Required EXP for level 2: 1000
Required EXP for level 3: 3000
ADAR 2-15 5.56x45 carbine
Colt M4A1 5.56x45 assault rifle
HK 416A5 5.56x45 assault rifle
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Desert Tech MDR 5.56x45 assault rifle
Assault carbines
Required EXP for level 2: 1000
Required EXP for level 3: 3000
AS VAL 9x39 special assault rifle
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Molot Arms Simonov OP-SKS 7.62x39 carbine
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Submachine guns
Required EXP for level 2: 1000
Required EXP for level 3: 3000
HK MP5 9x19 submachine gun (Navy 3 Round Burst)
Required EXP for level 2: 1000
Required EXP for level 3: 3000
HK MP7A1 4.6x30 submachine gun
Required EXP for level 2: 1000
Required EXP for level 3: 3000
B&T MP9 9x19 submachine gun
Required EXP for level 2: 1000
Required EXP for level 3: 3000
PP-19-01 "Vityaz" 9x19 submachine gun
Required EXP for level 2: 1000
Required EXP for level 3: 3000
PP-91-01 "Kedr-B" 9x18PM submachine gun
Shotguns
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Designated marksman rifles
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Required EXP for level 2: 1000
Required EXP for level 3: 3000
VSS Vintorez 9x39 special sniper rifle
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Sniper rifles
Required EXP for level 2: 500
Required EXP for level 3: 2000
Required EXP for level 2: 500
Required EXP for level 3: 2000
Required EXP for level 2: 500
Required EXP for level 3: 2000
Mosin 7.62x54R bolt-action rifle (Infantry)
Required EXP for level 2: 500
Required EXP for level 3: 2000
Required EXP for level 2: 500
Required EXP for level 3: 2000
Required EXP for level 2: 500
Required EXP for level 3: 2000
Pistols
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Stechkin APS 9x18PM machine pistol
Required EXP for level 2: 1000
Required EXP for level 3: 3000
Glock 17 9x19 pistol
Required EXP for level 2: 500
Required EXP for level 3: 1500
Colt M1911A1 .45 ACP pistol
Required EXP for level 2: 500
Required EXP for level 3: 2000
Makarov PM 9x18PM pistol
Required EXP for level 2: 500
Required EXP for level 3: 2000
TT-33 7.62x25 TT pistol