I started my interest in BR cartridges some years ago when I came into a large number of new 7BR cases. Sometime around 1999 I built a 6.5BR upper for my AR15 using a 7.62x39 bolt and long hours turning down cartridge rims on my 7BR cases. This rifle performed very well even out to 1000yds with 140gr JLKs.
For magazines my brother and I modified standard AR magazines to work. The modifications were straightforward and reliable once we got it figured out. Of course this wasn't an ideal solution since there was just enough material left around the chamber to be safe but without the standard large margin of error one would like.
I shot this rifle at Camp Perry in 2001 and 2002. It performed quite well.
In 2001 I stopped by the Olympic Arms booth at Camp Perry where they were showing off their new WSSM uppers for the AR15 platform. It immediately struck me that if they can make a bolt for WSSM it should be simple to just put in the smaller .473 bolt face. I discussed it with them and they expressed interest. However, it was the fall of 2003 before they committed to a small run of bolts and 2004 before I took delivery. The initial batch of bolts went mostly to USAF shooting team members.
I didn't get my upper built right away and it was the spring of 2006 before I had the upper assembled. I chose 6BR this time around. My original magazines did not work with the new larger bolt. So I set about modifying standard AR magazines again. This required quite a bit more experimentation but I finally got it to work by switching to a center feed dual stack configuration like a large capacity pistol magazine.
Once it was working I took it to Camp Perry in 2006 where it performed fantastically. Not one to leave well enough alone I built a second upper in 6BRX the next winter and shot it at Camp Perry in 2007 where the system again worked very well. This same BRX was again successfully used at Camp Perry in 2008.
In 2006 I set out with a partner to build and sell these uppers using a production version of my magazine. This partnership fell apart in the fall of 2007. I then set out to find my own magazine builder and market these myself.