Quote "It is an unexplained phenomenon that slow burning powders can and do cause DR blow ups..
Matters not whether you agree with me but I'm making a case for the 3rd fastner."Un-quote.

Firstly can you please give the details of a single recorded instence of this phenonomum.

Most blowups of any kind can be traced to the use of the use of double charges of fast powders or bore obstructions. Blow ups with reduced loads are a matter of debate, but there is a body of opinion that suggests that the fast powder that occupies a small volume of the case imparts an initial imputus to the projectile. The proectile leaves the case at relitivly low velocity. The ignition of the powder then stalls as its burn rate is dependent on the chamber pressure. The projectile then stalls in the bore and the increased pressure then again increases the burning rate of the powder which is now the meeting the rear of a projectile that has a much greater inertia.
Which is why, for instence, high performance cartridges such as the Wetherbys are cut with chamber reamers that have an elongated throat or freebore. If you seat the projectile against the lands, pressures go through the roof.

Quote "Concider this theory:" end-quote.

I have, and as the tensile strength of correctly annealed cartridge brass is 19,000 psi the load would have to be seriously reduced or plainly incorrect for this to be a factor. I consider your theory to be without either merit or foundation.

Quote "Note: This theory applies to all types of actions obviously, but due to the rather weak design
of the s x s action compared to an O/U or bolt action, will most likely have a greater negative impact on the former." Un-quote

The force on the bolting of any hinge actioned gun is proportional to the distence that that force is applied from the fulcrum and the vector of that force. Therefore the top barrel of a O/U for any given force will exert more "opening" force on the action.
Thus if the force was applied exactly in line with the hinge pin then the vector would zero and the pin would simply be in shear. You could hold such a theoretical action ( although such obviously cannot be made) closed with your thumb or in a single shot action like the Ruger #1 one could hold the breachbloch in position with the finger and thumb. The further that force is perpendicually from the axis of the hinge pin the greater the tendency to force the action open rotationaly around the hinge pin axis.
Which is incidentally why the top barrel of an O/U gives greater muzzle flip than the lower.

Now give over.