First let me agree that the shoulder/ taper of the case has no effect on the bolt thrust. One detail needs to be discussed; In a dry chamber the friction between the pressurized and expanded cartridge head will hold the case forward (if that is where it winds up) until around 40,000 psi or so. The head is not stressed beyond it's elastic limit and contracts after the pressure drops. This observation is supported by several facts:
<br> In a chamber with headspace the primer firing (not the firing pin) will drive the case fully forward. When the cartridge fires the neck/shoulder will stay there. If the pressure is low the primer will push back against the bolt head and remain protruded.
<br> If you increase the pressure, or oil the case the case will lengthen to fill the chamber.
<br> Now comes the part that I think is right but haven't proven to myself yet. It would seem that if the case has enough pressure to break the static friction and move back it will exert the same force oiled or not. I have been playing with heavy loads in a 35 Remington that has a little headspace, and can span this pressure range. For an indicator I have been using a pressure sensitive film.
<br> Much has to be done to reduce the variables, but I do believe that much of what we read, including Ackley shooting the 94 Winchester without the locking lugs, is horse apples.
<br>Good Luck!
