Let Posts be stored in another table

Use save_post action hook as shown below but write custom insert/update queries to save information in a different table.

add_action('save_post', 'save_product_data');
function save_product_data($post_id) {
//verify nonce and all other code...
$title = $_POST['post_title'];    //example variable
$wpdb->query(
$wpdb->prepare(
" INSERT into wp_product_instore ( post_id, meta_key, meta_value ) values ( $post_id, 'post_title', $title )" ));
//likewise you save all other variables for the post.
}

PS: This code hasn’t been test run. Please modify to your need.