I think more has been read into the term than was originally intended, and the industry itself has relished that.

Thus 'best work' has morphed to 'best gun'.

The order sheet would say 'best', and since this originally started in London, with orders for sidelock guns, the idea spread that it only applied to these types.

Much ado about nothing.

"The price of good shotgunnery is constant practice" - Fred Kimble