7MM and twist rate
Berger's website says that 180's require a 9 twist and 168 require a 10 twist, yet I know several shooters that shoot very accurately a 1000 yards with the 168's. Is speed the issue? I understand Berger's position is that a 9 twist barrel will not stabilize a 168 bullet and accuracy will be hurt. Have others that shoot a 7MM find that 168's can't be shot accurately from a 9 twist?
You need to edit your post. You have it backwards. Any twist that will stabilize an 180 grain Berger will also stabilize the 168 grain. Not the other way around.
I shoot both Bergers but I have an 8.5 twist, just to be sure. Especially when shooting at sea level.
Frank I shoot a 9 twist with 162&168 bullets. Look how Pyers was shooting with 168 bergers with a 8.5 twist. See you in april.
The 168 Bergers shoot tighter in my 284 than I could ever get the 180s to. This is with 3 different barrels, 2x 9" and 1x 8" twist.
That is what I have also observed but I'm challenging Berger's recommendations from their website. They very clearly state their twist recommendations and anecdotally their ballistician has stated that a 9 twist will not stabilize a 168 bullet.
When Berger says that you need a 1:10 twist to stabilize the .284 168 grain bullet they mean that you need a minimum of 1:10 twist to stabilize them. A 1:9 twist is a faster twist than the 1:10 so it will also stabilize the 168s. A 1:14 twist (slower) will not stabilize the 168s and a 1:12 probably will not stabilize the 168s.
You can believe these guys If you go to the 'Twist Rate?' thread in General Discussion and scroll down to a post by pbike, he attached a spreadsheet, bulletstabilitycalc.xls, that will compute the minimum required twist for the optimum stability factor (between 1.4 and 2.0 seems best). I believe this is the Don Miller Twist Formula. Prominent shooter and ballistics expert Brian Litz works for Berger, so you can believe what Berger says. To generalize: the longer the bullet the tighter the twist, which is inches per revolution. If you don't have sufficient twist it won't matter what you do, it aint gonna shoot. nhk
Originally Posted by oneflyer
i've shot 100gr to 180's in a 9 twist thay all shot real good ! matter of fact i shot 130 MK sierra and 110 TNT at 1000 yards this past weekend made hits on a steel p-dog and g-hog .
Originally Posted by oneflyer
and on paper at 100 yards both bullets 5 shot groups eat a hole !
Spencer HV barrel 9 twist in 7mm08.
Twist rate example
Now that I've had my morning coffee
I shoot a .224 diameter 55 grain bullet, .812" long, in a 1:9 twist barrel, that gives me a stability factor of 1.77 (unadjusted for velocity or environment).
Ideally you want the stability factor to be between 1.4 to 2.0. In this example I could shoot that bullet in a 1:10.125 twist barrel (stability factor 1.4) to a 1:8.5 barrel (stability factor 1.99), but the minimum twist would be 1:10.125. I can shoot it in a faster twist though, which I do at 1:9. Most .223 Remigton factory rifles are 1:7, 1:8, 1:9 or 1:12; but if I chose a 1:12 twist I'd have a stability factor of 1.0 which is too low (slow). I could shoot the bullet in the other 3 twists, although 1:7 stabilizes (2.93) the bullet, the best choices would be 1:9 and 1:8 (1.77-2.25).
Bottom line: You want the minimum OR faster. nhk
Last edited by nhkuehl; 03-13-2010 at 11:02 AM.
Of course that's as plain as the nose on my face.
Originally Posted by nhkuehl
oneflyer, my dad said add more powder to the case, that will do it.
one flyer you need to get out of the basement more . I know what you need a nice long drive to De. next week . 9 twist worked for me at 600yds.
More powder is sage advice--I'll do it!
See ya soon Scotty!!!!