.468 Bore vs .472 Bore Horns.
There is a very logical explanation as to why American horns are .468 and European horns are .472. It has nothing to do with playing style or sound color and more to do with nominal tooling. In the US, .468 is equal to 15/32 of an inch and .472 happens to be 12mm. When buying or designing tooling, keeping sizes to dimensions that are readily available (cutter sizes, stock sizes, etc.) helps keep the cost maneagable.
This may not be such a concern these days, tooling and machining costs have come way down and tools can be made or had at a multitude of different sizes. When a new horn is being designed these days, it may make a difference in cost to tool up at an odd size (but not much.) This is evidenced by the handful of smaller bore .460 horns that are appearing. What is important to remember though is that horn design is driven more by tradition and evolution than by engineering. While its true that makers today have a wider range of options than our predecessors, there is still quite a bit of gravity pulling us to the bore sizes and shapes that are “tried, true, and widely accepted.” Here in the US, that means 15/32 or .46875.
Does a .468 horn play differently than one at .472? It’s possible, but extremely unlikely that a .004 difference can outweigh the multitude of other design decisions that go into a horn. Since bore size would only apply to the straight sections of tube (around 6 ft), we are talking a total volume difference of under 1/4 cubic inch (.2124 cubic inches for 6 ft of tube). Considering that the bore of a horn is only actually as designed until one blows a chunk of peanut butter into it, this may not be the most important consideration when looking for a horn.