Bramble,

The hammerless double rifle by A. Grey for one...P.O Ackley In his writings as well...In fact He has blown more guns than anyone on the planet in the interest of internal ballistic science.
Several handloading manuals , I'll have to review my collection to cite the titles.

Talk about powder ? I'm talking medium burning powders i.e. RL 15 vs slower powders i.e. H4831 OR H 1000 Where duration of pressure and its effects are concerned.

Hey, bullseye will work ! why do ya think Fast burning/pistol powder is used in shotgun shells ???
Pressure spike is one reason..although you won't get the velocity one needs in order to generate enough power to kill anything larger than a goose..

Although I have not blown my shotgun/DR conversion, I can tell ya that it/ they (ALL GUNS) sure as "hell" kick alot harder (DYNO tested W/lead sled type of cradle) when using slow burning powder compared to the relatively tame recoil when using, say.. RL 15.
And frankly, It almost feels like the gun is going to come apart under the heavy recoil
generated when using slower powders.

Tom