There is currently a .30 cal throating reamer on flea-bay. In looking it over appears the end of the reamer is supported by the bore diameter surface and would be unsupported by a bore several thousandths larger (say a Marlin 336 microgroove). Am I understanding this correctly? I'd considered bidding as I have several .30-30s I'd like to lengthen the throats in, but I don't want to damage the throats with an undersized reamer.