KWA posts a video on Facebook showing the modularity of their Ronin kits which are now available at authorised dealers and resellers... "The Ronin 10 SBR, Ronin 18 SPR, and Ronin 15 Carbine kits are all great money-saving options when you need a second gun without the cost of a second rifle, but it doesn't end there. The kits are fully cross compatible with all rear-wired RM4 and VM4s, including the all-new RM4 SR10! One of the most popular choices is a Ronin upper on our VM4A1 or RM4A1 for the ultimate upgrade! The kits are available now at store.kwausa.com."