I was browsing thru ShotgunNews magazine....
I noticed that all the sellers have tons of 1:9 twists for sale, and an occasional 1:8 for varminters and "sniper/target" rifles.....but very few 1:7 twists were available.

Also, I noticed that everybody's offering chrome-lining for the 1:9's now.

Just thought it odd that 1:9's are still so available and that the "mil-spec" 1:7 was so elusive.

Ya'll did a group buy and bought'em all so the rest of us couldn't shoot anything over 70grains , didn'tcha????

here

1:9 shoots a wider range of commonly available bullet weights, and is thus more popular. Your average AR buyer is not concerned with the twist rate being the same as uncle sam's.