Peak pressure does not bare on the breach face as Heym sr20 suggests.
You may find the rifle cases bare less in the breech due to higher presser causing the case to stick to the chamber better than a shot gun hull!
If this was not true how come a light spring can hold a bolt shut on semi automatic rifles of blow back design?
Agree with what you say that the cartridge case does grip the chamber walls and thus you don’t get the full force of the cartridge coming back, but break action rifles still need to be made strong enough in the action to withstand the additional forces imparted by a rifle cartridge. They will usually have a third bite, a dolls head or cross / kirsten type bolt to provide additional strength.
As for comments on blow back designs of semi / full auto - they are pretty much all rimfire or pistol calibre. Things like the sten or sterling smg fire from an open bolt so that you have forward momentum of a heavy bolt to hold the case in the chamber till pressures lower. Others such as the MP5 use a roller mechanism to delay the opening.
Most pistols have a barrel / slide that recoil together that unlocks the barrel, the slide then goes rearwards to eject and picks up next round on way forward.
Semi or full auto using full power high velocity cartridges with pressures of 50,000 psi using some form of locking bolt. This has various forms. Early ones where toggle type mechanisms - vikers hubs etc, later tipping bolt as in the FN FAL / SLR or the rotating bolts as M1 Garand or the AR type and many other modern weapons. These are unlocked either by a recoiling mechanism (early machine guns or via a gas type system - both of which effectively unlock the bolt as you would on a bolt action or straight pull rifle.
A full power rifle cartridge needs a good locking mechanism to contain the pressures. The brass would let go if you didn’t have such mechanisms in place.
Back to double rifles, vast majority are built on rimmed cartridges- 450/400, 470 NE etc are these all operate at much lower pressures - 40,000 psi or less sorts of levels. Still substantially higher than a double shotgun but less than full pressure bolt action cartridges.
Those that are built in the smaller bores - 303, 7x57R etc are built strong.
