Copy posts from one Custom Post Type to another. (It doesn't handle post attachments for now)

cpt-to-cpt.php

<?php
add_action('admin_init', 'foo_duplicate_posts', 99999);
function foo_duplicate_posts(){

	// Only allow admins to run the script
	if(!current_user_can('manage_options'))
		return;

	// Check if keyword is set
	if(!isset($_GET['duplicate-posts']))
		return;

	// Check if keyword matches
	if($_GET['duplicate-posts'] !== 'magic-password')
		return;

	global $wpdb;

	// Configure post types
	$post_type_1 = 'post_type_one';
	$post_type_2 = 'post_type_two';

	$query = $wpdb->prepare("SELECT * FROM $wpdb->posts WHERE post_type = '%s'", $post_type_1);
	$posts = $wpdb->get_results($query, ARRAY_A);
	
	foreach($posts as $post){

		// Post info is already stored in an array
		// Set the post_type to the new post type
		$post['post_type'] = $post_type_2;
		$source_post_id = $post['ID'];
		unset($post['ID']);		// Remove ID
		unset($post['guid']);	// Remove guid
		
		// Insert new post
		$new_post = wp_insert_post($post);
		// Proceed if new post was created
		if($new_post){
			// Print a success message to the screen
			//show_message("{$post['post_title']} was duplicated from #$post['ID'] to #$new_post");
			show_message($post['post_title'] . " was duplicated from #" . $source_post_id ." to #".$new_post);
			
			// Get source post's post meta
			$post_meta = get_post_custom($source_post_id);

			// Convert all postmeta to new post
			if(is_array($post_meta))
			foreach($post_meta as $k => $v)
				update_post_meta($new_post, $k, $v[0]);
		} else {
			// Print an error message to the screen
			show_message($post['post_title'] . " was not duplicated.");
		}
	}
	// Stop the admin area from loading to get a clean reading of our output messages
	exit;
}
?>

Taken from http://wordpress.stackexchange.com/questions/66862/duplicating-custom-post-type-and-its-posts#answer-66905 and corrected few problems