.45 caliber in a derringer? It CAN be managed if you want to do so. Elizabeth Saunders of ADC recommends 6 rounds max at a session and she is correct. There are too many "old wives' tales" that influence us unduly. "The .22 rimfire mag in a handgun will deafen you even with ear protection" is another. Enjoy our hobby wisely and responsibly and leave these old saws at the door to the range.