I had a great range session this afternoon to wring out my new Colt 6920. The cabine had a few mods done by ADCO who does great work. The buis are standard M4 Matech flip ups and they were surprisingly accurate. I shot Winchester 55 grn Q3131 Winchester 62 grn M-855 Federal 55 grn XM-193 All functioned well with the best groups going to the Federal XM-193, my Colt loves this stuff. I mounted my ACOG TA-11 which fits perfectly over the Matech BUIS with Trijicons TA-51 mount. The ACOG is the perfect optic for this carbine and makes accurate shooting boringly easy. Any forum members who have ACOGs know just what I'm talking about. What really impressed me though were the Matech BUIS. I always thought these were just that, strickly back up sights should your optic fail. But these are really great iron sights and I could use them all day long even with my 65 year old eyes. I've owned several ARs over the decades and this Colt is one of the best.