HRC on Bowie Knife Spine?? (spine ...tempered/drawed)

[PeterTheWolf]

What would be the ideal HRC on the spine of a Bowie/Machete made out of 5160 steel?
Given that the edge is 57-59 HRC and spine at about .160"-.187" thick and soft-draw for temper.
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[Ratman79]

An educated guess--- about 47RC