Pour buttermilk into a shallow bowl
In a separate shallow bowl, whisk together flour, bread crumbs, Old Bay seasoning, black pepper, onion powder, garlic powder, and Cajun seasoning
Dip shrimp in buttermilk, then dredge in the flour mixture. Shake off excess flour and place on baking sheet
Place oil in a Dutch oven or heavy pan and heat to 350 degrees F
Fry shrimp a few at a time 2-3 minutes. DO NOT overcook or shrimp will become rubbery. Remove to a paper towel lined baking sheet to drain. Serve immediately