In a moment of boredom. (Made sense to me at time of writing).
SAAMI states that for .243 Winchester
Bullet .243 - 0.003 (6.17 - 0.08)
Barrel bore diameter .237 (6.02)
Groove diameter .243 (6.17)
The document defines ‘calibre’ as the diameter of the bore and the diameter of the bullet.
For .243 Winchester at SAAMI standards the bore diameter 6.02, which is less than 6.17, which means that it is classified as a small calibre and lead can be used.
The bullet diameter at SAAMI standards is 6.17 - 0.08, so if manufactured to max tolerance it would be caught in the large calibre however if manufactured within the -0.08 tolerance it would be classified as a small calibre as it is less than 6.17. When I’ve measured 6mm bullets they have generally come in at 6.15.
The ‘and’ in the calibre description is important. Does the ‘and’ mean that the description applies to both the bore and the bullet and have to be taken together or it won’t meet the calibre description or does it mean that the same criteria apply to both with no connection in which case ‘calibre’ has two differing interpretations. The sort of thing barristers make lots of money arguing.
Basically the documents are poorly thought out and worded, no wonder there is so much confusion.