I checked several and averaged the dimensions. The specific measurement you show was 2.915". But if he is starting with a full round barrel blank with the chamber and bore centered, a 3" blank won't cut it.
The barrel locking lug on top finishes about 1.309" from the centerline of the bore to the top. But the bottom pivot lug measures about 1.606" from centerline to the bottom flat. Add to that the fact that the lower lug is 1.06" wide, making the maximum dimension from the centerline to the extreme corners about 1.668". So a round barrel blank with centered bore would have to be at least 3.336" diameter, or better yet rounded up to 3.375".
I'm sure originals were made from forgings for strength and to reduce waste. But the cost of a forging die vs. a pile of chips in a modern CNC should make the decision to go with 3 3/8" blanks pretty easy.