Simple plugin that requires users to be logged-in to see any posts from a "projects" custom post type.

projects-restriction.php

<?php 
/**
 * Plugin Name: Project Access Control
 * Description: When a post of post type "project" is displayed and the current user is not logged-in, they are redirected to the login form.
 * Version: 1
 * Author: nikolov.tmw
 * Author URI: http://paiyakdev.com/
 * License: GPL2
 */
/*
	Copyright 2013 Nikola Nikolov (email: nikolov.tmw@gmail.com)
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License, version 2, as 
    published by the Free Software Foundation.
 
    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.
 
    You should have received a copy of the GNU General Public License
    along with this program; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/
 
 function proj_restr_check_auth() {
 	// If we're viewing a "project" and the current user is not logged in
 	if ( 'project' == get_post_type() && ! is_user_logged_in() ) {
 		// Redirect the user to the login page.
 		// They will come back to the current page on successful login
 		auth_redirect();
 	}
 }
 add_action( 'template_redirect', 'proj_restr_check_auth' );