He was the leading first-class wicket-taker every year from 1962 to 1965, and although limited-overs cricket showed his bowling could be hit, Shackleton remained very economical up until his retirement from first-class cricket at the end of 1968 – still among the top ten wicket-takers in the country. He played a few limited-overs games in 1969 and 1970, and played for Dorset for a number of years after this, showing he still retained his skill in the 1973 Gillette Cup. As of 2007, he has the seventh-highest tally of first-class wickets, behind Rhodes, Tich Freeman, Charlie Parker, Jack Hearne, Tom Goddard and Alec Kennedy. Shackleton has the most first-class wickets of any player who played his whole career after the World War II. He was also economical, with 35% of his overs being maidens, and conceding an average of only two runs per over.