If we look at it from a pure machine design aspect this becomes a bit more clear for a couple of reasons.

If we study how loading occurs once the firing pin has fallen we see a couple of things. Begin by examining how the whole system is loaded once the ignition occurs... the inertia of the firing pin acting on the case for sake of argument is a negligable force.

Once the round "goes off" the you have a radial pressure resulting in a hoop stress of the barrel. at the same time you have a linear force pushing on the bullet, chamber (assumption bottle neck cartridge) and the bolt face (assumption that headspace is correct ). Assuming both the radial stress and the linear occur simultaneously we can deduce that the bolt face is acted upon and barrel channel under chamber first. The whole action flexes to some point due to barrel expansion and the bolt thrust tries to seperate the threads. The bolt thrust being the major line energy transmission thus transfers the "recoil" force to the barreled action and thus to the stock and finally shooter. The recoil is transmited through the bolt, to the bolt lugs which are an integral portion of the receiver. Since the stock is clamped (thru bolted) to the receiver the friction between the two sets off movement of the stock. This gives way to some minute amount of movement between the action screws and recoil lug then loaded against the stock.

Now considering this scenario lets look at some of the geometry within the system. Right off you have a moment in the system which flexes the action. Barrel lifts and naturally causes deflection of the stock downward. The action screws stretch to some extent and the tang is forced against the stock. Exaggerated the action would look like a U. Naturally a shorter moment arm (receiver) would be stiffer and deflect less. Next is the relationship of the bolt to the recoil lugs and bolt face to the actual case. If none of these are square you don't evenly transmit the energy down the C/L of the action. This also results in a bending moment on the receiver. IF both recoil lugs do not have contact (as say many remingtons don;t) and the bolt face is not square to the head of the case the bolt will be loaded in a moment. Now assume both recoil lugs are in contact but still a non square bolt face... the case will put pressure off center and still result in a bending moment , using the bolt as the lever arm.

One thing that a long action has going for it is the length of the bolt and distance between the raceways. For a given clearance a bolt will have a greater angular defection as the supports are moved closer together. Once the sear falls away and the firing pin falls there is nothing but the bolt face relationship to case head and bolt lug to receiver lug relationship holding the bolt in alignment.

In the case of attempting to stiffen a long action, or even a short a one piece scope base is beneficial if securely bedded to the receiver.

Reckon this was a quick and dirty synopsis and there are many more factors to take into account.. but the main point is that a short action will deflect less due to length and stiffness for a given load imposed in the system.

Jamie