The pressure issue with double rifles has nothing to do with the strength of the action and never did. A 12 gauge will put as much or more back thrust on the action as most rifle cartridges. I've seen two examples of double rifles blown up. Both went out through the side of the barrel without damage to the action.

The reason pressure was an issue is extraction. The double simply does not have the mechanical advantage a bolt does on extraction. You don't want sticky cases in a sticky situation. The biggest improvement here since the advent of smokeless powder has been in the cases them selves, not the rifles. The original problem was at it's worst with nitro for BP loads in the old thin BP cases and in BP chambers that were a bit pitted.

Modern steel is an improvement on the old, but the old was quite up to the job.