To use the military sling as a shooting accuracy aid on a break action firearm is inviting accuracy problems. You are putting a side deflection on the barrel/forearm that can cause accuracy to go south in a hurry. By nature they are not as solid as the one piece stock designs. When all the variables in each individual application is considered, a carrying strap is more useful. I don't remember the proper setup as my M1 days were in the early 60's, but I soon gave up the idea for its use on a sporting rifle application. Just my thoughts, FWIW. Sorry I didn't have the answer for your post.
