I tested the M76 yesterday and it really is a very powerful weapon. In 30' gameplay there was only one opponent which didn't got killed with one shot.
But I have a better idea about preventing ppl from spaming with it. Why make the aim even more move-sensitive. It probably is heavier than other weapons so this should be ok.
Other weapons are good IMO, except the shotgun shots should have more spread.

BTW, is it just me, or are the terrorist's weapons more "enjoyable" to use?

Yes, that's true. But then cqb would need way more complicated damage model than is currently used. And it is questionable how it would work in-game.

I agree Harpoon, if the larger weapons hindered movement more and were slower to bring to target they'd likely be more balanced, but who's to say it would feel good in game...that's where the dev(s) (Coroner) would have to play-test and fine-tune it. In the end it comes down to personal preference. Maybe pistol rounds should have less damage ... idk but with the armor these guys seem to be wearing....

Real life values (with empty magazine and no accessories):

-M76: ~4.2 Kg
-Ak47: ~ 4.3 Kg
-SG 552: ~3.2 Kg
-SCAR: ~3.29 Kg
-REC-7: ~3.5 Kg

Can't find the dry masse of M110 (approx 7.2 Kg with scope/bipod, w/o magazine).

Also real values:
M76: ~ 1135mm
AK-47: ~870mm
SG552 Commando: ~730mm
SCAR-H: 770mm (min)
REC-7: 823-902mm (stock is collapsible)
M110: ~1029mm

The larger guns (M76 and M110) are much longer than any other rifle listed. Thus, they are much more unwieldy and awkward and have a much greater moment that the operator must contend with. Even if there masses are similar.

Having shot both an AK47 and a (civilian) SMD-R (AR-10 derivative, just as the M110, which is ~4.5kg fully loaded and 1000mm) I would not hesitate to say the the AK47 has a much shorter time to target and is quicker overall.

Valid point.

I guess that the weapon in TC:CQB is not AK47 becose it has side rail mount and nobody really used that gun. AKM is more common and has side rail mount. Weight of it is 3,4kg.

If so, it would refer as a AKM...

Could be a Norinco type 56 (chinese copy) which also appear to have a side rail mount ability...
Slightly the same weight as the AK47: ~3.9 - 4.03 kg...

Anyway, since Kalachnikovs were copied to death, it could be anything else...