I'm no engineer, and I hesitate to get into this debate, but I find it difficult to believe that a bolt action is not inherently stronger than a hinged double rifle action.

Whether you are talking about breech pressure or "backthrust" (which obviously doesn't exist in the absence of breech pressure), I think the focus would be on the mechanics that maintain the face of the breech securely tight against the end of the barrel, so that the whole mechanism stays closed.

On a bolt gun the major part to accomplish the task is the receiver ring. Typically the end of the barrel threads into the receiver ring - an extremely strong connection. The bolt closes from the rear by rotating its locking lugs into the locking lug recesses of the ring. All these parts are massive and operate in direct line with the bore to directly contain the "backthrust". There is no torque. It is a very strong mechanism.

On the other hand, the receiver of a hinged action rotates on the hinge to close the end of the barrels. The fasteners are on the lumps (Purdey) located forward of the end of the barrel and lateral to the line of the bore. There may or may not be a third fastener, of various designs. There is great debate whether the third fastener does much of anything. With the "backthrust", strong torque is applied to the action. This torque applies force to the bolts and lumps, and it has the advantage of leverage derived from the length of the bars. The weak point is in the apex of the "L" where the standing breech meets the bars. That's why some actions are "bolstered" or reinforced. As an aside, I will tell you that I know a man who has a drilling, the action of which cracked in this very location, on both sides.

Intuitively I can't imagine that this hinged mechanism is as strong as the bolt mechanism. In support of that statement I point out that the falling block action is very similar to the bolt action in that it contains the breech directly in line with the bore by way of lugs in the receiver directly behind the bore. The only mechanical difference (as to lockup principles) I see is that the block slides into place rather than rotate into place. I'm no expert on artillery, but the field pieces I have seen appeared to operate on the same principles as a falling block. Why not hinge those actions?

Obviously, action size is part of the strength equation. I have no doubt a hinged action can be made to contain the .50 BMG. I doubt you or I could lift it.

Extraction is not an issue of strength. Some bolt guns are designed for great extraction, i.e. Mauser 98; some are poorly designed for extraction, i.e. Remington 788, Weatherby Mk. V.

I'm sure I am sitting here with my foot in my mouth, and as I pull it out I apologize for my uninformed opinion.

Best to all,
Curl