I disagree. I use 95% lead 5% antimony and don’t get loose hooks ever no matter if I pour with cold or hot hooks. I think soft pure lead is the corporate. People tend to pull the jighead out the mold by the hook which will cause the loosening or have molds like Do-It that have too thick sprue and are hard to get off the head which can cause the loosening if not careful. Print a lure and Jacobs mold have excellent sprues with little lead at the head. You can twist the sprue off cleanly unlike do-it molds. I quit using Do-it molds and pure lead along time ago and loose hooks are no longer a thing. One way to stop loosening if you are using soft lead is stick the spout of the pot directly in the gate of each cavity. This allows lead to get into the head hot as possible with less cooling as if you poured the lead across the top of the mold which I see many do.