'Stretch' marks are likely just scratches. Brass that has stretched an inordinate amount will show a bright ring around the case just in front of the extraction groove. A light wire with about 1/8 inch bent to form a hook will allow you to feel if a 'groove' was formed on the inside of the case from it's stretching. It's likely OK as the springfields are very strong. Mausers are prone to impringting when a blue pill is fired but not the springfield. Still with any military rifle it's a good idea to get them checked. Most any good smith can run that check in just a few minutes..