well, this was made in another Patch a LONG time ago. in the new Patch D12 new weapons came, and the old ones was erased. As a result, many ships you see in the workshop are now unarmed and have no guns. you have to add the MAC cannons yourself.
here is what you do:
- Get the biggest gun you can find (must be smaller than the frontal part ofc)
- Place it on top of the frontal parts, both lower and upper part
- Use the advanced positioning-arrows to place it perfectly inside
PS. if it lights yellow and still won't place itself inside the ship you must place it on top when it doesn't light yellow. Click "Connect part to ship" and the press the gun, click "Modify" and then lower it.
If you have any problem, please notify me ;)

I'm new to this game but how do you shoot the MAC cannons?

Why do not make the Infinity ?

This is unbelievably awesome

<3