You need the components
And you need for them a couple of reasons - the components are consumed (they disappear and the ammunition is actually used in the attack) and the action requirement is also stated in the spell description.
Material Components in Spellcasting (PHB, 203)
A character can use a component pouch or a spellcasting focus [rangers do not have access to a focus] (found in chapter 5) in place of the components specified for a spell.
If a spell states that a material component is consumed by the spell, the caster must provide this component...
Conjure Volley (PHB, 226)
You fire a piece of nonmagical ammunition from a ranged weapon into the air...in a volley from above and this disappear.
Conjure Barrage (PHB 225)
You throw a nonmagical weapon or fire a piece of nonmagical ammunition into the air to create a cone of identical weapons that shoot forward and then disappear.
Both of these descriptions first require that you DO something with the ammunition (not just have it) AND that the ammunition/weapon disappears (and is used and possibly not recovered) after along with it's counterparts.