OK

Using the link you've given, which is I think the current law, S5(2) seems to say that the expanding missiles (or bullets, to normal folk) described in S5(1A)(g) are prohibited ammunition.

If they are prohibited ammunition, they are ammunition, and need to be recorded as such.

I think the Guidance refers to "expanding ammunition or the missile for any such ammunition" together not because they're treated separately, but rather to remind us that they are treated the same!

S5 bullets count towards the holding allowance because they are themselves ammuntion. I can't see how they could be ammunition in the holding allowance, yet not on transfer.

They are either ammunition, or they are not: and the Act seems to say that they are.