These kits or packages are are add on kits you can purchase for most guns that simply upgraded the gun you currently to a sniper level gun. I can change it easily coming from a pistol grip to a straight grip and this can help me to drill into places which can be hard attain. http://aikdubai.com/__media__/js/netsoltrademark.php?d=random-ids.com%2F__media__%2Fjs%2Fnetsoltrademark.php%3Fd%3DForum.pinoo.com.tr%252Fprofile.php%253Fid%253D1020339