Lets say we have a Dragon born with Volume=v (v=xyz), Mass=m. It's Density would be d=m/v. We also know that it kick ass with a Force=F, where F=m*a, being a the acceleration of it's arms while punching.
If our DB double it's size in every dimension, it means that it's Volume is: V'=2x2y2z > V'=8(xyz) > V'=8V.
If we assume it's density keeps constant, then it means it gains some mass.
D=m/v, but now D=m'/v' so
m/v=m'/v' , mv=m/(8v) , m8v/v=m' , m'=8m
If we assume that it will punch with the same acceleration as always, F=m*a
F'=m'a, F'=8ma F'=8(m*a) F'=8F
So, changing from medium to large would imply changing 8 times the strength. If this keeps up for every step, then we are talking about one extra change to get to huge, and then one to get to gargantuan . So 8^3 times the force. And if we assume a linear relation between force and damage, 8^3 times the damage...
I think if you're just Huge and you're grappling a Gargantuan dragon, you're going to look like a dog humping his leg. Which may be what OP wants to do, but still...
But you only deal 2d4 extra damage. I think, if you can grow your hands to the size of horses, you should deal just a bit more damage.
Doubling the size in each dimension should at least double the damage
My (very briefly) Gargantuan Wild Shaped Dire Wolf salivates at this thought.
Math time!!!!
Lets say we have a Dragon born with Volume=v (v=xyz), Mass=m. It's Density would be d=m/v. We also know that it kick ass with a Force=F, where F=m*a, being a the acceleration of it's arms while punching.
If our DB double it's size in every dimension, it means that it's Volume is: V'=2x2y2z > V'=8(xyz) > V'=8V.
If we assume it's density keeps constant, then it means it gains some mass.
D=m/v, but now D=m'/v' so
m/v=m'/v' , mv=m/(8v) , m8v/v=m' , m'=8m
If we assume that it will punch with the same acceleration as always, F=m*a
F'=m'a, F'=8ma F'=8(m*a) F'=8F
So, changing from medium to large would imply changing 8 times the strength. If this keeps up for every step, then we are talking about one extra change to get to huge, and then one to get to gargantuan . So 8^3 times the force. And if we assume a linear relation between force and damage, 8^3 times the damage...
Yeah... A few extra d4s seems.... Meh
I was thinking it was a grapple thing, but Huge is already big enough to grapple anything.
I think if you're just Huge and you're grappling a Gargantuan dragon, you're going to look like a dog humping his leg. Which may be what OP wants to do, but still...