Claymore uses high explosives and will take out a whole squad in line formation, whereas a blunderbuss uses low power black powder (like fireworks) and effective against one or two men at most in a single shot, with little barrel length to contain the expanding gasses.

A pistol grade vest would protect you from blunderbuss shots, where even a rifle level plate vest would simply aid a claymore in completely dissecting your body at the joints and midsection.