From my understanding I think this is what you want. I had a mag 60 with explosive secondary and bullet primary fire on left and right mouse click lol its a killer weapon but its been awhile though since i was focused on it xD.

This would be a script function you need to do a script, search for this through the scripts to understand.

if((self.Owner().Buttons() & BC_ALTFIRE) != 0)

Its actually applied to the ridingGun.txt in scripts folder that will help to understand some I believe look for ALTFIRE in that document.

Looks like a nice update there I updated this post too with new info and new download.

https://turoksanctum.com/f-e-a-r-weapon-sounds-for-turok-2/

Moved this to Turok modding. Though I kind of want to have a separate place for vanilla mods. But there won't be enough. And I wanted to keep this in the original place but it may be overlooked by not being in mods.

Good job there nice update.

 

Finally got around to making a video of this one.