Welcome back.
Your scene contains too many things so that it is hard to isolate individual problem, also not clear what you call 'master control' - there is no nodes named that way.
I took the machine gun from your previous post (with my fix for belt aiming) and assumed that the master control is mg_control circle (MC). I ScaleConstrained root to the MC and disabled SegmentScaleCompensate for entire root hierarchy - this helped to get rid of gun twisting while scaling MC.
Then, added MC-ScaleConstraints to every belt_rig joint AND belt_curve_rig group - this ensured that motionpath scales with MC and every bullet maintains its relative size.

There was somewhat irrelevant chain of constrained locators for aiming (yaw+pitch) the gun, which I reduced to a single locator/node, like gun_control circle; up_objects were parented to their relevant parent node, like MC. To sum things up, as much as I tested, scaling (translating and rotating too) MC works correctly.
See if you can apply this to your full scene.
,,,_°(O__O)°_,,,
Maya2019.1 @ Windows10 & GeForce GTX1080Ti
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