I ordered keymod with heavy barrel , because they have none in stock for a few wks, I can still make a few changes, they are going to install a CRT stock and adapter and give me a credit for the OEM stock. I've looked at page , where you can build your own rifle and it appeared you can choose rifling , maybe it's for the m - model only. Oh and I've ordered an S&J linear comp. here's my thoughts on the SU16.. If Ivan get a new barrel and receiver for$400, I'll have the tactical stock conversion kit + Red lion aluminum forend , which is a $450 value. So new barrel receiver and stock and forend, I should get $800 for it .cost me 400 to make $400. Or sell it as is for what?