I was pretty sure I had this right...
This is where the sounds appear to be located in q4base:
pak010.pk4\sound\weapons\machinegun
I made a pak013.pk4 archive by copying another one from the game directory, and modifying its contents with WinRAR to fit these:
pak014.pk4\sound\weapons\machinegun\fire0.ogg
pak014.pk4\sound\weapons\machinegun\fire1.ogg
For the new .ogg files I used renamed copies of clipin.ogg and clipout.ogg. I'll probably use something cooler later.
I downloaded a machine gun mod someone else had made and the included instructions:
This mod doesn't work either. It has to be something else I am missing?Extract the pak013.pk4 file to your Quake4\q4base directory.
If you already have a pak13.pk4, rename this machine gun sound effects pak file to pak014.pk4. If you already have a pak014.pk4 file, rename this machine gun sound effects pak file to pak015.pk4 and so on if there's another sequential pk4 file.
More simply put, this machine gun sound effects pak file needs to be the last pak file number in your q4base directory.
Load Quake 4 and the new Machine Gun sounds should work right away!