AR2201,

The way you seem to be using the term backthrust would make it the exact same as bolt thrust in bolt rifles. Thus the force is not specific to DR and as 500 Nitro pointed out is exactly the same as a shotgun built on the same style frame. In fact all cartridges have a "backthrust" as you call it when fired. The largest contributer to the amount of back thrust is probably cartridge design. Generally the more body taper to any case/cartridge the more "backthrust" it will exerpt on firing.

BB