a replaceable cutter shell mounted over said rolling cutter shell, said replaceable cutter shell having an annular tapered inner surface that mates with said annular external surface of said rolling cutter shell, said annular tapered inner surface having {HEAD ~ a slope} at {TAIL ~ an angle} within the range of substantially 2° to substantially 40°; and 
a replaceable cutter shell mounted over said rolling cutter shell , said replaceable cutter shell having an annular tapered inner surface that mates with said annular external surface of said rolling cutter shell , said annular tapered inner surface having { HEAD ~ a slope } at { TAIL ~ an angle } within the range of substantially 2 ° to substantially 40 ° ; and
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