In my original which I sent in to ETO, there were 2 sound files, gun_8x303_browning.wav and gun_x8x303_browning.wav. They are identical, in fact, but one is for external sound, and the other internal.
My "read-me" says:
Drop both wav files into CFS3/sounds(folder)
Drop AvHistory_gb_gun_8x303cal.xdp into CFS3/guns folder
Find the following lines in CFS3 root/sounds.xml:
<c303>
<no_damage>
<sound file="xgun_303_browning.wav" FileInt="gun_303_browning.wav" Stereo="Yes"/>
</no_damage>
</c303>
Paste this immediately after:
<c8x303>
<no_damage>
<sound file="gun_x8x303_browning.wav" FileInt="gun_8x303_browning.wav" Stereo="Yes"/>
</no_damage>
</c8x303>
And before:
<c792>
<no_damage>
<sound file="xgun_792mm_mg81.wav" FileInt="gun_792mm_mg81.wav" Stereo="Yes"/>
</no_damage>
</c792>
The result looks like this:
<c303>
<no_damage>
<sound file="xgun_303_browning.wav" FileInt="gun_303_browning.wav" Stereo="Yes"/>
</no_damage>
</c303>
<c8x303>
<no_damage>
<sound file="gun_x8x303_browning.wav" FileInt="gun_8x303_browning.wav" Stereo="Yes"/>
</no_damage>
</c8x303>
<c792>
<no_damage>
<sound file="xgun_792mm_mg81.wav" FileInt="gun_792mm_mg81.wav" Stereo="Yes"/>
</no_damage>
</c792>
Finally, drop the xdp file into the ETO Spitfire folder. For any aircraft you wish to use this sound for, simply
substitute "AvHistory_gb_gun_8x303cal" for whatever the entry was in the original xdp file. Delete the bdp file afterwards.
If you check Rob's instructions, you should find all the bits. If it still doesn't work, send me a PM with your e-mail, and I'll send you the package.