I think the movement is almost identical, but chopping is a strike, and pressing is a neutralization.
Your intention should be different during each.
During a strike, it is a quick burst of energy. During a neutralization you're deflecting another weapon, attaching, and adhering.
Good question. Its important to really understand each movement, especially if you wish to train these as qigong. Because remember, the Yi (intention) leads the Qi (energy). Your sense of enemy and your intention need to be focused while you slowly practice, coordinated with your breathing, in order to lead the qi efficiently and correctly.
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