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 a slope at {HEAD ~ an angle} within {TAIL ~ the range} of substantially 2° to substantially 40°; and 
within
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 a slope at { HEAD ~ an angle } within { TAIL ~ the range } of substantially 2 ° to substantially 40 ° ; and
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