There were 7.62 caseless magazines UI pictures in the alpha and beta, maybe these were planned and then scrapped again. Possibly we're going to see a 7.62 caseless rifle with the campaign?

But, +1 on this. It'd always be nice to have more guns, plus, Nato right now has no direct competitor to the ABR. A belt fed MG would be nice too. But we -need- animations for those.

The MXM used 7.62 in the early alpha, but it was changed.
/didn't vote

@InstaGoat

Do you mean there aren't any animations for the Mk200 and the Zafir?

Well 6.5 is almost same as 7.62 in case of damage.But looks lighter.
I think it will matter if default ammo will be 5.56/7.62 like.
But anyway wote up.Current arsenal is very weak to me.ArmA2 had moar weapons AFAIK.

7.62x51 has almost 50% more energy at 1000 meters, so damage does actually differ. Due to that, it's still much better cartridge for a marksman rifle. Source: http://www.shootersforum.com/rifles-rifle-cartridges/8865-6-5-grendel-vs-6-8-spc-7-62-nato-5-56-nato.html

(I'm assuming the bullet is of "Grendel" type, because the rifles caliber is described is 6.5×39mm caseless)

@DarkWanderer.
In game this isn't work.5.56 have 8 points of damage,6.5 - 10,7.62 - 12 :)
Well,at least in config.And also any of them have almost same ballistic.
And also 6.5 in game isn't grendel.This is fictional caseless ammo.

@samogon:
These values work only at reference velocity. The game has simulation of ballistics, meaning the damage will be scaled with distance and velocity drop.
As for Grendel, I've already said this is an approximation. But this approximation is better than just naive "Well 6.5 is almost same as 7.62".

"Almost" is a bad word here. 5.56 and 7.62 are also "almost" the same. The devil is in the details.

Closing - too unlikely to be added