File Upload directory permissions

I am uploading files with the paperclip plugin. I have a /public/photos
directory which is a symlink to
/home/username/public_html/ I have
entered the following command, in an attempt to set the permissions on
that directory:
sudo chmod -R 2750

However, when I upload a new photo, the permissions on the folder
holding the files, and the files themselves, are all 777.

Am I doing something wrong with setting the permissions with that
directory, or is this something with paperclip?