Thats the thing, using multi grip with full grips doesn’t, you would need to unlock an axis of constraint in order for it to rotate like that with a physical grip. Also it doesn’t “glue” to the motion controllers at all, it would be finding a median between the two controllers, in fact it shouldn’t by default be behaving correctly for you at all without tweaking so it may be not even having a rear grip for you currently (multi grip would have to be on).
For it to function somewhat like that, you would just need to figure out which hand you want to be rotation free and call SetPhysicsHandleSettings and set the axis that you don’t want to be constrained on that hand to off.
With a gun tools script active the weapon orientation component will dictate what direction the constraint is facing, you can use that to make it easier to know which axis’s to turn off. The melee tools grip script does that by figuring out which hand is in the rear and which is in the front and handling constraint limits based on that.
If you wanted a literally accurate version you could also just use a physics prop script on the weapon and you would have to face both hands in the same direction and align them to aim the gun, no free rotation around a hand at all.