I just had a thought, and needed to put it down on paper (or electonically).

I reloaded some .30-06 the other night by neck sizing only (the first time I have done such a thing). I got to thinking today.

Is there a velocity difference between neck-sized and FL sized brass with identical loads?

Here is my theory behind this (not sure if it is valid or not, so feel free to correct me if I am wrong).
-When a round is fired it is "fireformed" to that chamber, so a certain amount of the pressure, or "energy" is used to change the dimensions of the case. This is for a FL sized case of course.
-When neck sized cases are used, they fit closer to the exact chamber dimensions of that peticular rifle, so upon firing, less "energy" is used in changing the dimensions of the case, there-fore allowing more "energy" to be used to push the bullet down the bore at a higher velocity.

So I ask -
Is this theory bunk, or does it have a valid point?

Now, I am sure even if it is valid, the benefits of a higher velocity would be quite minimal, probably within the extreme spread of the load, given the climatic conditions are exactly the same (ie: temp, humidity, elevation, etc.).

So, what do you all think?