DD,
Something is not to scale in the drawing. I think it is the barrels.
The barrels are 4.5" long.
46 divided by 4.5 = 10.22
The wheel is 3"
3 X 10.22 =30.66"
A 30" wheel is too small for that carriage.
Doing the same thing for the carriage only will give him a 7' long trail on 42" wheels which I feel would be alright for a 46" barrel.
Zulu
Is the drawing 90 degrees to point of view? Does it look right?
What is the length of the trail in the drawing, multiply that by the scale multiplier? That would be the correct scale length to go with a 46 inch barrel.
In your example the scale factor is 10.22. So if as you say the wheels measure 3 inch in the drawing they should be 30.6" wheel. If 7' trail is the scale length product of multiplying the drawing length by 10.22 (8.1 inches or so,) then that is also correct to fit a 46" barrel.
I have no idea where you came up with 42". The bigger those wheels are the smaller that barrel is going to look.
Those drawing in round shot are pretty good drawings. Heavier, longer barrels will have proportionately smaller appearing wheels.