That is an interesting thought. It is obvious which would have more recoil, but bolt thrust I am not sure is related, I think it (bolt thrust) is more related to pressure, and the case (or rim) diameter....the recoil (I believe) is generated and varries based on the speed of the bullet as it travels down the bore, bullet weight, as well as the muzzle blast, which with more powder, especially unburned powder, creates more muzzleblast.
Another theoretical thought, if you got a ase with the diameter of a Lapua, but made it so short that the total case capacity was that of say a .308 win, and loaded it to say 65,000 psi and shot a .338 caliber 300 grain bullet out of it (would obviously be slow) and then shot the same bullet out of a .338 Lapua at 65,000 psi, would the bolt thrust differ between the two, or remain the same?
Ok. First, Recoil is a chain reaction. It begins at the bolt face and transfers thru the lugs into the abutments to the recoil lug into the stock and to your shoulder.
so a 7 lb gun that makes 120 ft lbs of recoil puts twice the force on the lugs that a 7lb gun that makes 60 ft lbs of recoil. Don't get confused between felt recoil which is dependent on rifle weight. Regardless of that weight, the initial energy transmitted into the lugs remains the same.
E=MC2 The question is how that energy is transmitted
i was attempting to keep it simple. The amount of powder determines the pulse length and available energy. Yes a heavier bullet and a lighter bullet at the same charge weight will result in lower chamber pressure on the lighter bullet and less thrust on the bolt lugs.
Lets go a different direction. A 50 bmg only makes 53,000 lbs pressure. Is there any doubt a 50 would Push the lugs on a .710 bolt right into the abutments and then shear them off? Its the available energy, the resistance to that energy, the area that energy is spread over and the structure resisting that energy that create the opportunity for set back.
now you could put 43 grains of H4350 in a 308 case and then put a 500 grain bullet on top of it and probably blow your gun up because chamber pressure would be 100k or so.
i think the point Kirby might be making is the available surface area on the lugs are such that when absorbing the energy of a 338LM launching a 300 grain bullet at 3000 fps will cause the lug to indent the abutment and (set back) before you might see dangerous pressure signs on the case. This could be a cumulative effect that happens after repeated below max pressure firings in a LM.
With most cartridges with the case lock up to the chamber wall, the rearward force of the case against the bolt are insufficient to dent the abutments before the brass shows pressure signs. I think Kirby might be saying that in the LM that might not be true. At some point some round will exceed or tempt the engineered limits of an action. How will those limits manifest? What happens when the case is more resistant than the action, as may be the case with the LM case. Personally, I suspect SS actions might yield to this before carbon actions. With the LM You have a huge case base that puts the max limit of pressure on the bolt lug faces to where they overcome the surface integrity of the abutments.
As I started, few people have Kirby's experience with max rounds in really big gun in almost all available actions. Id just take his opinions to heart.
