I would think if you want to build a model it would pay you to purchase a set of plans for either gun. The D&E is a 1/3 scale model of the 1874 Colt. In addition they have the plans for a very nice field carriage as well as the tripod. The RGG is also a very nice design and is more robust with the cocking switch safety and a much better ejector setup. Either set of plans is only $50.00.

the dimensions of the following are for the D&E 1/3 scale design so X 3 should give you a rough idea of the size of a full size gun:

Barrel length: 12 3/16 plus a .5 thread end. Overall total 12 11/16

Barrel diameter: The barrels are tapered with a 3/8 x 2” hex on the front. It tapers from .414 just behind the hex to .465 at the start of the thread.

Gun body (breech casing?) outer diameter: 2.375”

Gun body (breech casing?) length: Overall length is 4.512” which includes the .200 x32tpi on the end.

Nor sure just how much help the above will be but it will give you a relative size.