If we take the Striker’s example of 500kg per cubic meter then a space missile at 1/20 of a dTon comes in at around 360kg each which seems a bit more realistic.
A Sidewinder is around 85kg, an AMRAAM about 160kg, and an AGM-88 HARM (which looks like a super buff AMRAAM) is around 360kg.
However, these are long super pointy atmospheric missiles and it’s likely a space missile would forego the aerodynamics instead being optimised for use in vacuum. Doesn’t mean you can’t fire them in atmosphere and while, being unstreamlined, their top speed would be severely curtailed being grav powered they’d likely be quite agile - if you’ve got nothing to shoot them down it’s going to be a bad day.