i have had the same issue twice from ndt. very aggravating. it was not the movement. i made a scraper out of a triangluar file and cut the ring down to allow the movement to drop in. the second time i chucked up a round diamond stone in a jewellers drill press and carefully with small cuts got the ring cut down and then scraped it. the scraper is just very hard steel and hollow ground on a wheel minding heat build up not to loose the temper