You have to unpack its WeaponsFramework - Main.BA2 with Archive2 or Cathedral Assets Optimizer, then delete that same BA2 and the extracted Meshes folder, and install any of its patches for Tactical Reload and/or See Through Scopes if you use these mods. If you still get the same crash...
To check if Buffout 4 is actually working, you can inspect xSE Plugin Preloader.log inside your Fallout 4 install folder or f4se.log inside Documents\My Games\Fallout4\F4SE folder after running the game at least once. You should see a message that Buffout 4 and other DLL mods loaded ...