HO guidance 2014 Para 2.12 ( component parts for ammunition are not subject to controls) states

"There are two exceptions to this. The first is missiles for ammunition prohibited under section 5 of the 1968 Act, for example, expanding or armour-piercing bullets. Such missiles are themselves defined as ‘ammunition’ and are subject to control accordingly (see Chapter 3). "

So ordinary bullets are not subject to controls but expanding projectiles are, and should be stored accordingly.