Okay, often associated with CSM but sometimes used by Assault Marine, what would be its stats?

My guess:

Astartes Chain Axe:

Damage: 1d10+5 R
Pen: 4
Special: Tearing, Unbalanced
Wt: 16
Req.: 5
Renown: -

Seems decent. I'd raise the req a bit - to 6/7, just because it's not as common as a chainsword.