I know you've already responded,but I hope you don't mind me adding a note.
When I was 25 and a first time mom, I was hoping to keep toy guns out of my house, after all guns are dangerous. When my oldest boy was about the age of your boy he picked up a spoon at the breakfast table and created his first gun. Now I have 4 boys and yes,an arsenal of toy guns, from wooden to water, toy swords and shields, even light sabers. Instead of banning them, we have learned about being protectors and knights that would defend their family's honor. We talk about how never to engage an unarmed person and never to point a weapon at self or another person...we do target practice mainly, at nonliving targets ( although marshmallow shooters are fun if everyone is joining in.) We are constantly learning good ways to handle difficult situations through negotiation/words/kindness and peaceful conflict resolution...
toy guns are just something to play with, and pretend bravery with, not to perpetuate evil with (that's for bad guys and my guys don't like bad guys)
My six year old likes little army guys and makes up strategic battles with sound effects.
You have to know they are the gentlest boys around, and other boys like to play with them. They know that if someone is not having fun then the game is over...usually everyone involved is rolling on the ground laughing silly when they finish. To be honest they didn't do a lot of this this summer, the war games with pretend swords peaked at about the age seven.
My oldest does desire to serve in the military one day (he's eight) and I praise him for his desire to do something noble, to protect his country. I pray that our country will never need his bravery...my mother hen instinct desires nothing more than to keep him safe...but it also means that I can't deny him part of his innate masculinity. Being a hero is part of this. As a woman (and civilizing force on society :) I can encourage him to learn the correct way of handling these issues through play. Oh, I almost forgot to add...my boys are musical too...they played the violin for a couple of years and are now doing piano lessons...they prefer sports...but do the music for mom :)
Good luck as you decide how you want to handle this...What does Dad think?