If like me you have a rifle without sling swivels, and don't wish to alter the gun, here's a simple solution to adding a sling. Cheap too, the paracord cost less than £1.
Step 1: Measure Your Cord
I found that twice the length the rifle was an ideal length of cord to start with. and four times that length for braiding.
Step 2: Forming the Attachment Loops
Double the sling cord, and knot the end.
Pull the circle of cord straight and loop the unknotted end around the barrel, allowing enough cord to pass over the front sight. Tie a knot in the doubled cord.
The same is done at the stock end.
You now have your basic sling.
Step 3: Adding the Braiding
Double the braiding cord and knot to the sling below sight end.
Pull the sling cords straight and loop the left cord under them and the right cord over. Pass the cords through the loops, and pull tight. Repeat ad infinitum until you run out of cord and knot the ends.
There are better tutorials on Instructables on how to braid, I recommend you view them as they use two different colour cords to demonstrate the procedure.
Step 4: The Finished Sling
The sling is easily fitted by forming a double loop on the end and passing over the barrel and stock.
Step 5: What Would I Do Different?
I didn't tension the sling cords, this allowed the braiding to twist, as I weaved it. So I would make a simple frame ( broom handle and 2 nails!) to do this.
I would also add toggles in either wood or leather to hold the cord close to the gun.