Don't know if they are still making them, but I have an Armalite
.243 AR 10 that is extremely accurate. Soon it will be approaching the 1000 round mark and I fret what I will do when the accuracy deteriorates. A couple of years ago I purchased a 6x6.8 for my AR 15in the hopes it would replace my .243 when I finally shot it out. In my case the accuracy of the .243 is consistently far superior to that of my 6x6.8.