Originally posted by MrDraco
View Post
Howa mini-action in grendel to be released in mid-2016
Collapse
X
-
I read on another thread here on the forum that the twist rate on the prototypes is 1:9. I strongly recommend 1:8 for the 6.5 Grendel.
If you go to Berger Bullet's Twist Rate Calculator and enter in data for a sort of worst-case scenario — 6.5mm 130 Berger AR Hybrid at 2450 fps at temperature 0 and altitude 0 with a 1:8 twist — you get a "comfortable" stability factor of 1.61. Good article on this by Litz here.
Changing only the twist rate to 1:9, you get "marginal" stability of 1.27.
To get back to comfortable stability with a 1:9 in those conditions — let's say you're on the Alaskan coast in winter — you'd need a muzzle velocity of 4,000 fps!
Howa: Please, change the twist on your 6.5 Grendel mini-actions from 1:9 to 1:8 before these go into production!
P.S. If you're trying to be efficient by using the same barrels as your 6.5x55s, they, too, will benefit going to 1:8.
P.P.S. Bryan Litz tested velocity loss from twist rate increase and found it averaged only 1.33 fps per inch of twist rate. So if your 1:9 shoots 2601.33, then your 1:8 will shoot 2600 fps.:: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets
:: I Drank the Water :: Revelation 21:6 ::
Comment
-
-
Originally posted by BluntForceTrauma View PostI read on another thread here on the forum that the twist rate on the prototypes is 1:9. I strongly recommend 1:8 for the 6.5 Grendel.
If you go to Berger Bullet's Twist Rate Calculatorheretested velocity loss from twist rate increase and found it averaged only 1.33 fps per inch of twist rate. So if your 1:9 shoots 2601.33, then your 1:8 will shoot 2600 fps.
From my personal experience... And I'll upload pictures tomorrow... I shot nothing but sub 1" three shot groups at 100yards with factory Hornady superformance sst 123gr rounds. Wind was around 10-12mph. I managed to keep the 20" HB to .800" center to center and the 22" std bbl to .720" with the 1-9 twist.
Comment
-
-
Originally posted by BluntForceTrauma View PostI read on another thread here on the forum that the twist rate on the prototypes is 1:9. I strongly recommend 1:8 for the 6.5 Grendel.
My 20" 1:9 twist J&T keyholes 127LRX's at 100, and shoots the 140SGK's with mediocre accuracy. If I were to buy another AR grendel barrel, it would definitely be a 1:8 twist. I'd still be seriously interested in a 1:9 Micro, but even more so a 1:8 :-)
Comment
-
-
Originally posted by GSPHunter View Post+1
My 20" 1:9 twist J&T keyholes 127LRX's at 100, and shoots the 140SGK's with mediocre accuracy. If I were to buy another AR grendel barrel, it would definitely be a 1:8 twist. I'd still be seriously interested in a 1:9 Micro, but even more so a 1:8 :-)
Comment
-
-
-
GSPH, right on! There are a lot of us here just dying for something like this.
Doing it right the first time with a 1:8 will just compound the success, as glowing accuracy reports start coming in from all ranges, bullets, and conditions.
According to Litz, having a less-than-optimal BC doesn't necessarily affect accuracy at 100 yards, only that it "means, in practical terms, that your bullets drop more quickly and deflect more in the wind.":: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets
:: I Drank the Water :: Revelation 21:6 ::
Comment
-
-
Originally posted by Matt @ LSI View PostI have personally shot all three models, and achieved sub 1" groups with factory Hornady ammo. This from a 20" rifle with a 3-9 power scope. I really don't think you'd have to ever worry about keyholing @100 with this setup.
Comment
-
-
Glad to see these rifles on the way. One configuration that I think would be $ is a youth model, there is not a better youth cartridge IMO than the Grendel, rifle can be light weight, accurate, smaller sized and still not recoil while being effective further than most should be shooting.
Comment
-
Comment