Look at that man. Look at how he moves. I will admit that the gifs aren’t the best, but until I get my hand on a bootleg copy of WS and a gif-making programme, please bear with me? I can still illustrate my point.
One of the chilling and brilliant differences between Bucky and the Winter Soldier – which is thanks to Sebastian Stan’s acting, so, thank you for that, gorgeous! – is how different their body language is. The Winter Soldier is a machine, a weapon; every movement, every gesture, is precise and for a specific purpose. He walks straight and doesn’t shift his body weight more than necessary. Another gif I considered using was this one

because it also shows that conservation of energy. There is no flailing, no hesitation, not even a moment of “oh shit, this is gonna hurt”. Just a smooth roll and down with the metal hand. This isn’t just training, we’ve seen our heroes do almost the exact same stunt. And they always have a perfect look of “oh shit, I didn’t plan this at all”. Not the Winter Soldier. He just assesses the best way to return to his original plan. Efficient, sparse, cold. A perfect weapon.
And then we have Bucky. Look at that swagger. Look at those shoulders and hips move, his straight back, his cocky everything. He’s a peacock. When Bucky sashays down the street, he wants your attention.
Now, part of this I think is entirely 100% Bucky, but I also think he played it up back home, as a protection mechanism. Because if everyone payed attention to the rakish Bucky Barnes, then no-one would bother little Steve Rogers, right? I’d say I have support in this theory, because even when Bucky is out on the front lines and snipes with the Howlers

he is still miles away from Winter Soldier. Look at that arm twist; it’s full of unnecessary force and movement. That is an expression of anger, because some HYDRA goon dared to try and attack Steve. There is nothing cold about Bucky during the war – in fact, I’d argue that he’s so hot with rage that he burns a still, blue flame.
There is a hell of a difference to feel so much that you achieve a sort of pseudo-calm, and being dead inside. Bucky is the former, the Winter Soldier the latter, and Sebastian Stan gets that across without being in-your-face about it.
(gif sources: rebloggy.com & fanpop.com & forums.superherohype.com & bucky-wintersoldier-barnes)