The reason why some US rifles converted to T spec have UKmade 5 groove barrels could be down to the fact that the original spec was that the rifles should conform exactly to the spec laid down. And that spec was drawn up while the norm was the original, early spec. - 5 grooves, split foresight block band etc etc. So original spec it had to be. But later common sense prevailed and as we now know, plenty of two groovers and solid block foresight block bands passed through the doors.