On this video I try playing three Trevor's missions (Mr. Philips, Trevor Philips Industries and Crystal Maze) with muskets and marksman pistol only, while the enemies also only have muskets.

Here's the code I made for this: https://github.com/EnforcerZhukov/GTAV-GlobalWeaponsModifiers/blob/master/MusketWeaponsForAllPeds.cs

Watch more videos from the series "GTA V but...", where I play main missions with mods that make them more fun or interesting: https://www.youtube.com/playlist?list=PLeA0hbZK4VaoH_OdcHre87T_3ZYgXmc-k