Our break barrel rifle sling has mounting hardware for the rear sling post on the gun and strap & buckle for the forward sling loop.
Loosen the sling post hardware by unscrewing the security screw. Push the knob so the gate opens. Swing the gate so the hardware can be inserted into the post. Swing the gate back into position and tighten the security screw.
Now run the tag end of the strap through the forward end and back through the buckle. Adjust to fit.