Hello Glen,
Tins change quite often, which is probably the reason wrecked of us collect them.
Whilst the front of the tin always says 4.5mm, it is the sticker on the back that shows the content size.
They are also available in 4.49mm.
I have noticed that some of my 4.5mm R10s fall through my pellet box and get lodged.
Not quite seen a pattern to explain this though.
I would more than likely say is the tolerance of the tray, rather than the pellets being so far out, but possibly a combination of both?
Kind regards,
Phil