I have seen a Cutts blow apart. The guy was shooting handloads with plastic shotcups. I saw a lot of them with plastic hanging out of the sleeve with the old W-W Mark 5 shot collars ears ago. The one that blew, split maybe two or three slots from the muzzle end. I could speculate forever, but I don't really KNOW what caused it. I do know they were designed for the pre-shot collar/cup ammo. A Poly has the slots at the end so it would appear to be lower risk, and I have never heard of the end of one blowing off. I have seen them split a collar.