Here I created back side of a gun using revolve with 180 degrees, and then created two planar surfaces

Group the base parts as one

Group upper parts

Then create the gun tube

Go to modify/snap align objects/align to move one object to another.

Group the tube to itself and use modify/center pivot. The tube and the group now have the same pivot.

Then select tube and move it up. Groups, pivot stays in place.

Select the group. Then go to duplicate option box, and make 5 copies at 60 degrees. You can make instances.

Create rings around the tubes.

Group moving part of the gun. This part will aim up and down.

Create locator. And align it to gun.