S size. Certain you may need some force, but this is due to the fact that the fast regulate buckle is held in position by friction. This may be the weak point to another person but I have found this to become of no problems for me, the sling has https://smith-wesson-m-p-15-22-ma63074.articlesblogger.com/57127044/everything-about-magpul-pmag-d-60-ar-m4