Pete,
Hold your horses and do some checking on barrel weights and calibres.
This from Dunlap;
"The “C” model barrel is 1/16 of an inch larger across the flats; therefore, increasing
the weight by approximately 1/2 a pound over the same caliber “B” model barrel"
That means half a pound heavier in Same calibre, between B and C profiles,
The difference between a B in .50 and a "C" in .54 is going to be Less.
I know what you wrote earlier about the barrel weights, but some of those are wrong, because when they write "4.2 Lbs, they mean 4 lb 2 ounces.
If they were Right in what you posted above, I am sure they mean 3 lb 11 ounces and 4 lb three ounces, so we still come back to half a pound difference at Very most, as Dunlap says.
I'd look at the weights a Lot closer before I decided if I were you.
I have one I made for my son, 38" Haines barrel in C weight, and I wouldn't want it any lighter for anything.