MeowersI can't say exactly whether or not are mine considered 'double-engineered', but I got them from Sirius I think, if I remember correctly, and then applied the capacity upgrade
You actually don’t even apply any upgrade to them. They are a pre-engineered module which comes with an additional heatsink charge compared to the standard ammo capacity blueprint (which like what, only gives you one extra?), by throwing some materials at a tech broker on one of the Sirius ships.
I did expect it would probably just be one of those but it’s not like Frontier like to make things clear in their wording.