What is the difference between the Colt 6920 compared to the Colt 6721 other than the 6721 has a heavy barrel and a 1x9 twist?
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What is the difference between the Colt 6920 compared to the Colt 6721 other than the 6721 has a heavy barrel and a 1x9 twist?
That's the basic difference. With the appropriate bullets, the 6721 will be more accurate than the 6920.
http://www.box.net/shared/static/6po0sh394g.jpg
http://www.box.net/shared/static/8yz2obnogj.jpg
barrel profile, twist ratio and rollmarks
The previous posters nailed it (twist, HBAR).
I've owned both. Still have the 6920 and would buy another in a heartbeat.
Didn't care for the extra weight of the 6721. Not one bit.
Is there an advantage to an HBAR vs an m4 profile in a 16 inch rifle?
Accuracy. The pic below shows a comparison between a Colt 16" HBAR and a Colt 16" M4 (government profile) barrel. Three 10-shot groups were fired from each barrel at a distance of 100 yards. The 10-shot groups were over-layed on each other using RSI Shooting Lab and the mean radii were calculated for the 30-shot composite groups.
http://www.box.net/shared/static/d4f59k22os.jpg