if i were building a casting rod  from a blank does it matter if it is a spinning blank or a casting blank  is there a difference   does a casting blank know it will be used for a spinnning rod?

if i were building a casting rod from a blank does it matter if it is a spinning blank or a casting blank is there a difference does a casting blank know it will be used for a spinnning rod?

It does matter, a spinning blank is slightly less powerful than a casting blank.

You take for example a SJR782 vs a MBR782, in theory both are medium power fast action blanks, but the SJR is slightly less powerful than the MBR.

It does not matter as long as the action and power of the blank are suitable to your needs.

I agree the blank doesn't know what it will be. But I do!..

I personally will only build a BC rod on a Casting blank, and same with a Spinning blank (mainly because of tapers).

Just my .02¢

Tight Lines!!!  

Most* spinning blanks are a little lighter (not to be confused with slower) in the mid section.  I've used them to build as cranking or trebeled bait, casting rods for those who don't like slower actions.

I build my own spinning rods on casting blanks. (preference for the way they feel)