107 Sierra a real shooter
Almost everyone in my group shoots it. I'm the maligned Hybrid shooter, but I know they can hear the steel ringing even though they appear not to...
When the Berger 105 first came out Berger said the minimum twist was a 1:8 twist and after a couple of years they changed it to a 1:7 twist. I called Berger and talked to Brian Litz the Berger Bullets Ballistician and asked him about this change. He said some further testing resulted in the 105 Hybrid twist rate change and also the Berger Twist Rate Calculator was changed to reflect this. After the calculator change my stability went from the Comfortable Stability area into the top of the Marginal Stability area with the BC being compromised by 2% and it showed a new minimum twist rate of 1:7.75. Brian said not to worry that I should not have a problem with the twist rate of 1:8 and that appears to be what I have found. I am not sure what the elevation is where you shoot but at 1000 feet elevation, 80 degrees and bullet speed of 2800 FPS a twist rate of 1:8 is optimized, I shoot at sea level. With all the variables that apply you really need to use the Berger Twist Rate Calculator to check the twist rate needed. The published Twist Rate on the bullet box or advertisements cover a generic situation and not necessarily yours.
Here is the link to the Berger Twist Rate Caculator.
http://www.bergerbullets.com/twist-rate-calculator/
I also looked at a newer box of Sierra 107 HPBT MatchKings and they also say 1:7 twist only. I believe that was also a change from 1:8 a few years ago.
Good observations. Guessing many do not realize how altitude affects ballistics, even though they might plug in the variable