Hmmm. I would argue that the stock, especially in the head area is the weak part of the round action/blitz design. So much wood has to be hogged out to accommodate the trigger plate, etc. The "fillets" of the stock are often very thin and prone to damage. The stock design doesn't allow much error for bending either....kind of like a Darne, if the RA stock doesn't fit, best to move on.
The hallmark of the Scottish RA is the strength of the action and its beauty.
Rimmed double rifles have obviously been built and have proven to be very successful on all the listed actions, so that point is moot.
I think (from what I've seen) that the head of the boxlock has more points of contact and broader points of contact with the action than the other two mentioned actions, therefore it would be the stronger head design of the two.
The less parts a gun or machine has the more reliable it will be, the easier it will be to produce, the parts can be built more robustly, etc. There in lies the technical advantage from one type to the next.
Depending on the type and design of SLE, like comparing a Rogers action to a Beesely/Purdey action is like comparing apples to oranges. One is actually pretty simple, the other is a beautifully executed Rube Goldberg that is very difficult to produce and maintain.
Boxlocks are pretty much the same across the board with a few exceptions of course. I think boxlocks beat out both in terms of design, function, reliability, ease of maintenance, manufacture of parts, assembly, strength, etc.
If we are discussing aesthetics and beauty....both the SLE, hammergun, and RA easily beat the BL. :-)
