No.
Would doing one arm barbell bench presses be easier than doing one arm dumbell chest presses if they were both the same weight. Since the barbell is much longer maybe theres more balance so its easier with it.

No.
Try it and see which one feels lighter.
definately not. i dont know anyone that does 1 handed BB presses but i do know it will take an incredible amount of hand and grip strength not to mention the ability to stabalize it and thats before you actually have to press it.
i do one arms w/db on med ball or smith machine one arms i neva hear dof omeone doing it just barbell not smith tho
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