Probably built_x64/panda3d/bullet.pyd and built_x64/bin/libpandabullet.dll. Note however that you can run Panda straight from the built directory if you don’t want to reinstall Panda every time. Just use the copy of Python in built_x64/python/python.exe to run your programs and it will use the copy of Panda straight from the built directory, no installation needed.