Critical Defense was made for smaller barrel guns like 3 inch and under to have good expansion and less recoil and muzzle flash. Were as the Critical Duty was made to penetrate barriers like wood windsheilds or metal like on a car and still expand and penetrate. i use the C duty in my gun its...
I had FTF probs with mine like the bullets were to big and sent it in and they replaced the barrel id just send it in and let Smith fix it. Got it back in under 2 weeks and works like a champ.