Barrel dimensions - estimates & rules of thumb?

[Naphtali]

What are reasonably accurate estimates for dimensions for 1-1/4 inch O.D. 30-inch swamped octagon, and also tapered octagon barrels with bore diameters .69-caliber for Plains rifle reproduction?

What would be dimensions for those barrel profiles that should keep the total weight of a maple stocked Plains rifle reproduction at nine pounds ± four ounces?

 

[Zonie]

For some recommended dimensions you might look at the Hessian Jaeger barrel in this link
http://www.trackofthewolf.com/List/Item.aspx/650/1

An old Track of the Wolf catalog says it weighs around 3.8 pounds.

Their tapered barrel selection looks like this
http://www.trackofthewolf.com/List/Item.aspx/651/1

None if them are 1.25 inches at the breech so your proposed barrel will be heavier.

As for the total weight, that's impossible to say.
The density of the wood, the size of the stock, the weight of the butt plate, trigger guard, sights, ramrod, barrel underlug (if used) present too many different combinations to give one answer to.