Use one of the following entries with the "mpcheat changeclass" code.

ak (AK47) 
ak74su (AK74SU) 
ar (SAW) 
at4 (American rocket launcher) 
b (M870 shotgun) 
d (SOPMOD M4A1). This is exactly the same as class "sf" with one exception, class 
D comes with three mines, which you can get by entering the bind 6 grenademine 
console command and pressing 6 (or any bound key of your choice). 
g (M16A2 with grenade launcher) 
gp (AK47 with grenade launcher) 
m4a1 (M4A1) 
m4m (same as sf but with different grenades) 
d (SOPMOD M4A1) 
m9 (M9 pistol) 
mos (Mosin-Nagant sniper rifle) 
pso (AK74SU with a scope) 
r (M16A2) 
rct (no weapons or grenades) 
rpg (Rocket propelled grenade) 
rpk (OpFor machine gun) 
s (M82 sniper) 
s24 (M24 sniper) 
s82 (M82 sniper) 
sf (M-4 silenced) 
spr (Special Purpose Rifle) 
svd (Dragonov sniper rifle) 
v (VSS Vintorez)