Hey Dale... I put the slug between two files of equal depth... medium or coarse., usually medium. Roll back and forth a few times with the top file.. rolls the bullet between the two files. I’ve done this on several of my slugs that weren’t shooting just quite right. Tightened up my groups. I try to give a bullet a fair shake, shooting fast, slow, sized,lubed and unlubed. Last resort, I knurl them. If non of the above work, I figure it’s the wrong design for my particular twist rate. Sometimes, like you’re 24 grain .22 and 33 and 45 grain .25 swagged, it’s just drop in accurate in my guns.
Haven’t heard back from mike but hope to.