(Numbers below from memory, please forgive me if I'm not right on the money)

I don't understand how a 30-06 will barely make 2400fps with a 220gr bullet and a 35 Whelen will put out a 250gr at 2500fps or more.

How is this possible? Are these wildcats chambered so that the bullet is just barely held in the case? I've noticed this with other conversions as well (like 308Win and 358Win). Can anyone straighten me out on this?

Its called bore expansion, meaning that it has a larger bullet base (piston) for the pressure to act upon for roughly equal bullet weights. This is enhanced since the equal weight in the larger bore will also be of shorter length and have less surface bearing on the bore, hence less friction. All dependent on equal pressures.

There's more surface area for the powder to push on. Look at the same bullet weight in a 25-06 and 30-06 or 243 and 308Win, you'll see the same thing happining with the 30cal being faster in that case.

The same thing happens in reverse after the bullet leaves the muzzle, the larger diameter bullet having more air resistance.

Force=pressure X area . F=PA
Force = mass X acceleration. F=ma
If the pressures are the same in two calibers than that with the largest cross sectional area yields the larger force.
If than two masses are the same the larger force produces the greater acceleration.

A larger acceleration over the same barrel length yields a higher velosity.

And all this time I thought my schooling was wasted.