Dear Ralph,
Depends of rifling shape the real diameter may a little differ due do different tools using for rifling. A little difference may take place also due to measurement method. For example. When I made slugging by soft lead and push it trough the whole barrel length - I had got 11.03 mm (0.434). When I used another method for slugging the result was a little, but different. I have used the rimm of brass of 38 Sp. (rimm diameter was 11.10 mm). I have pushed it into the barrel for about 10 inches, but then pushed it back. The result was the 11.05 mm (0.435). The lead is soft, but the brass is hard.

We have to take in account my shape of rifling. My maximal diameter not corresponds to the grove diameter in classical typical rifling. My rifling is octagonal, but classical is round.

I used handmade jacketed SP bullets. It was very good for moose.

I made experiments with .44 cal (0.429) jacketed handgun bullets (Sierra). I think that it’s diameter is a little small for me.

I will try to find the 425 Westley Richards bullets (.435 dia) and to decrease a little it’s diameter. I suppose that the best diameter of jacketed bullet for me will be – 0.4325-0.4335 (somewhere very close to 11 mm), but for the lead bullet it will be about 0.433-0.437 (11.0 - 11.1 mm)

Also I suppose, if Your barrel is 0.43300 diameter (as assumption). The best jacketed diameter for You will be somewhere between 0.4325 and 0.4329.

Here You will find an interesting article about using of led bullets in Marlins. The table about diameters of bullets in the end of second link is especially interesting.

http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/17
http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/19
http://www.beartoothbullets.com/tech_notes/archive_tech_notes.htm/28