Bullet in the case depth

[Mr Underbridge]

So I was looking at comparing 6.5 cartridges.
I was wondering how the amount of the bearing surface of the bullet inside the case neck affects the accuracy of the bullet?
What are the general rules of thumb? What happens if there is too much or too little?

 

[shoot4fun]

I've been told that it is best to have at least caliber length depth inside the case but no rule written in stone that says there is a minimum depth.
I would think a lot of it has to do with what the purpose of the load is going to be. IE, you wouldn't go hunting with bullets out so far they were jammed hard in the lands or had a risk of them coming out of the case just thru normal handling. On the other hand, I shot a lot of 6PPC rounds with the bullet just barely seated in the neck and had some success.
My preference is not to seat any bullet below the juncture of neck-shoulder if at all possible. My 257 Roberts is one where bullets have to be seated very deep below that point to fit the action/magazine so there are exceptions to every "rule".

 

[watercam]

My .308/155.5 Palma loads only have .100" of bullet shank in the neck. As long as they are straight and you are not feeding from a magazine they shoot fine. If I drop the ammo box I would worry though...

 

[ireload2]

If you examine the entire wide world of metallic cartridge shooting you will find there are a lot of variations and most are related to ensuring reliable assembly and feeding of the ammo.
There is a branch of shooting called Schuetzen in which many of the competitors do not even seat the bullet in the case. The bullet is seated into the barrel breech of a single shot falling block rifle followed by a charged case. These are very accurate cast bullet shooters.

So there is not a one size rule to fit all ammo.
A machine gun needs well fixed bullets to work in belt fed machine guns maneuvering at high G's in an airplane.
A single shot rifle only needs the ammo to stay in one piece in your pockets. If you are a bench rest shooter it does not even need to last in your pockets.
Accuracy is not high on the list of priorities in some applications and in others it is a high priority. You have to make the ammo fit the application.

So I was looking at comparing 6.5 cartridges.
I was wondering how the amount of the bearing surface of the bullet inside the case neck affects the accuracy of the bullet?
What are the general rules of thumb? What happens if there is too much or too little?