Custom weapon model trouble

Did you make it in 2 groups, gunname_base and gunname_barrel?

And the swivel point must be at the origin, move both parts together until the pivot point is at 0,0,0.

Then export the gun as Number of groups = 2, and group quantity = 1 for both groups.

Then last of all the hardpoint on the ship must have min and max angles more than 0.

What down? Like a weapon that goes through your ship with it’s barrel? Or you mean to make it rotate in 180° up (so it will be upside down)?

Yes, just rotate the ship hardpoint in HardCMP X=180°. To be sure, rotate 25° first and you will see if you got the right axis.