Mike, I know you have forgotten more about doubles than I will ever know, but I have read from many sources over the many years I have been shooting, that a doubles bullets will converge at some distance, otherwise how do they get there in the first place? It stands to reason that they will have to go in opposite directions before and after the convergence. Again, this may be ignorance on my part and others, but that has always been my understanding. Not saying you are wrong, just explaining where I come from.Not quite right Sestoppelman.
The barrels should be set to shoot parallel at any distance. If they cross at 50 or 100 they aren't set right or you need to speed up the load until they don't cross. But if they shoot wide they need to be slowed down some.
Many get the terms regulated at and regulated for mixed up. The 'regulated for' is simply the load used. 'Regulated at' is the distance that they were shot at during the regulation. There are videos at youtube that show this being done with Sabatti's so take a look and "guesstimate" the distance.
Greame Wright has covered this in his books quite well.
Did you use any filler in the 4350 loads? I'm not at home now and exactly half a world away (Ukraine) from my loading bench so I can't see how much airspace would be in the cartridges with 4350. Consider 1/2" backer rod or Dacron to fill it up to the base of the seated bullet with just a bit of compression when it full. I use a pencil to pack the Dacron into the cases. Backer rod is easier to use. Just cut to length and insert.