I am pretty certain that there are no 3rd party options other than keymod vs mlok and maybe length on factory seekins rails. You kinda have to be on board with the Seekins rail/receiver. That being said, I have had the ar15 sized upper that is pretty much the same as the SP10 for years now and it is a great rail for precision/dmr type guns even if I have the keymod version. The machining and finish are up with the best I own, LMT, Virtus, HK.