I have some Easton Carbon Raider, 55/75's, and some 65/80's. There are no other markings on the arrows.

Are 55/75's the same as 340's?

Are 65/80' the same as 300's?

I am trying to use Stu Miller Dynamic spine calculator.

Thanks,

On the arrows I have worked with the 55/75 is basically a 400.  I would say the 65/80 is about a 340 or maybe a little less.  A 300 is about a 75/95.  That may vary one arrow to the next, but that has been how the GT and Beman arrows I shoot compare for me.

Thanks

You can verify for sure, by calling Easton directly.