I noticed that some users ( PZ- Mods ) reported sound absence in the AR-15 . I also had this problem and found a simple solution. Follow:
Take corresponding .ogg sound file AR-15 weapon of any weapon mod and insert in Zomboid folder \ mods \ TommyGuns \ media \ sound \
Test ok in SP.
Builds 33.20, Build 34.28, Build 34.28 iwbums.
If you found any issuie please report to mod creator and community.