In Avengers: Age of Ultron, when the Hulk crumples the HulkBuster's hand, where is Tony Stark's hand?
..or is Iron man not actually in the HulkBuster?
Where is the Tony Starks hand?
Clearly it's still inside his original armour
As you can see from the above image, the HulkBuster "armour" wraps around the standard IM suits and is considerably larger than the original armour suit size.
Essentially, the whole of Tony is inside the HulkBuster torso. It's likely his actual arms don't even reach the shoulder joint of the HN armour.