What star level do you have it on?

Its is rank 2, And yes I am aware of the low dmg per shot(ignoring the full mag) of the gun through out the ranks of the gun, as follows:

1. 158 per shot / 15,800 per mag

2. 336 per shot  / 33,600 per mag

3. 424 per shot / 42,400 per mag

4. 533 per shot / 53,300 per mag

5. 665 per shot / 66,500 per mag

6. 827 per shot / 82,700 per mag

7. 959 per shot / 95,900 per mag

granted the double dmg chance gives the weapon a bit of power, its still gonna be measly, you would have to dump a bunch of ammunition to even do a scrach.

Also if you are wondering the max rpm 600 

When compared to the Minigun, it blown out of proportion. When I think of heavy duty I think of lots of ammunitio, and major damage. The only way I could find this damage acceptable would be if this had a faster rpm, because with the chain gun, I see it as a short gun fight weapon, its not meant to last 30 seconds fighting a mech. I see it as a way to dish ok damage really quickly allowing mechs to do dmg and hide behind cover.

Well this is the 8 energy version. The damage and shots seem comparable with carbine. 

While this is true, the whole magazine would have to be used to deal that damage

How long does the mag take to unload in carbine and chain gun?

5-6s for carbines and 9-10s for chain gun

Bro, I admit it. The Chain Gun's avialable version are weaker, though I did expect them to be better than Carbines, which they didnt even come close to. I mean overall, if we compare Chain Gun 12 (Coming Possibly in the near future) and Carbine 12, I would favour the Carbines.

mmmm disagree, i kill 1 or 2 mechs with a mag, but, the trick is to mount it in a mech with shield

Tbh I feel it would be cool if it had (with a bigger mag perhaps) a really high max fire rate

I agree, even with the damage buff, I think that the chain guns max fire rate could be doubled, without the use of a stupid legendary implant that well never get unless we dish out 100 dollars or "get lucky"