Great addition to jp enterprise scs - JP Enterprises SCS System Buffer Retainer Pin & Spring Kit

I use this on my 6.5CM build. It keeps the SCS assembly in place, but can be easily removed if needed. You don't need to worry about your SCS system falling out if your upper is open/detached. You cannot use the standard retaining pin because it will get caught on the SCS weights and will force you to disassemble the buffer tube to get the SCS system out.