Originally Posted by billyspey
Grand is closer to 3/4 heavier and GPX is 1/2 heavy. That is the way my shop tell,s me. I use the grand as a bass bug line on a sage XP in a 691 and a 790 XP
Your shop is pretty close, but here is what the RIO website says about the Grand line, verbatim.
"The RIO Grand is a full line size heavier
than the industry standard, and features more weight distributed towards the front of the line to easily load faster action fly rods."
Basically you are over-lining a rod when you buy a newGrand line matching the rod's weight.