Warning: I was about to scrap a hammer head until I tried a 220 grit flap disc on the eye
Picked up a beat up 3 lb cross peen at a flea market in Reno for $8 and the eye was so chewed up the handle wobbled no matter how much I wedged it. I almost tossed the head in the scrap bucket but figured I'd try dressing the inside of the eye with a 220 grit flap disc on a die grinder first. Took about 15 minutes and I got it squared up enough that a fresh hickory handle seats tight with just one metal wedge. Anyone else ever brought back an eye that far gone, or is there a better trick I'm missing?