Cook shrimp in a pot of boiling salted water until cooked through, about 2 minutes. Drain; rinse with cold water until cool. Pat dry and chop into bite-size pieces.
Whisk together celery, scallions, mayonnaise, dill, lemon juice, horseradish, vinegar, and paprika; season with salt and pepper. Fold in shrimp.
Meanwhile, heat broiler. Toast buns on rimmed baking sheet until golden brown, about 3 minutes. Spread butter on each toasted bun and fill with shrimp salad.
Recipe adapted from: www.bonappetit.com