I'm basing this on no particular time so their will be a lot of modern guns. The = will show what the pack a punched version is called.
M249 SAW, holds 100 rounds, high damage, slow reload = M115 chainSAW, 300 rounds, very high damage, mobility of Assault rifle
AK47, 30 round mag, normal reload, medium damage = AK69 hellfire, 50 round mag, normal reload, fire rounds, high damage, gets flamethrower attachment
MP5, 25 round mag, high mobility, quick reload, low damage = MP88 Negotiator, 30 rounds, high damage, very fast mobility, very high bullet penetration
F2000,35 round mag, assault rifle mobility, high damage = F-42000, 50 round mag, very high damage, pistol mobility, red dot sight and grenade launcher
Spas-12- 8 shell tube, high damage pack-a-punch is the same as blops
SIG MG710- 50 round belt, very high damage, low mobility = 1 SICK MFKR, 200 round belt, same damage, same mobility, 12 round underbarrel automatic shotgun (for when you run out of ammo)
Stoner 63, 30 round magazine, medium damage, low mobility = Blaz3d 420, 100 round mag, grenade launcher.
KS-23, 7 round tube, high damage = K155-ME, 12 round tube, fully automatic, reloads 3 rounds at a time.
Grim Reaper, four round rocket launcher, slow reload, very low mobility, can hurt player = N0 ph3ar, 8 rounds, same reload, LMG mobility, player is immune to splash damage.
Uzi, 32 round mag, medium damage, fast reload = U Luzi, 40 round mag, same damage, dual wield, quick reload
AA-12, high damage, low fire rate, automatic (of course) = AA+24, very high damage, faster fire rate, fires slugs instead of buckshot.
Benelli Supernova, 5 shell tube, high damage, pump action = Benelli Nebula, 12 shell tube, semi-automatic, very high damage.
Desert Eagle, 8 round mag, medium reload, low fire rate, medium damage = D3S3RT Hawk, high reload speed, fully automatic, high damage.
Pancor Jackhammer, 24 round mag, fully automatic, slow reload = Paincorpse Rock Drill, 50 round mag, fire rounds, ability to give up mag to use as mine using down on D-pad (damage depends on rounds left in mag.