308win 1/9 twist downside?

[tuckybill]

Got a Defiance Deviant short action/08 boltface off the post exchange(thanks Nbot). Now thinking of a 308 win with a 1/9 twist. I might want to mess around with some sub sonic loads but don't want to go down to the 300 blackout 1/8 twist. Anyone here shoot some of the lighter bullets in a 1/9 twist?

I could see where it would be neither fish nor fowl but I get good groups out of my .223 1/7 twist with light 55gr so why not go with the 1/9 twist in a 308? It should shoot good enough with 150s and still shoot the heavies and maybe some sub sonic stuff also. I've searched and can't really find much on a 308 winchester with a 1/9 twist. Plan on a cut-rifled varmint contour 24". Seems like it might be interesting.

 

[MidRangeCrisis]

Got a Defiance Deviant short action/08 boltface off the post exchange(thanks Nbot). Now thinking of a 308 win with a 1/9 twist. I might want to mess around with some sub sonic loads but don't want to go down to the 300 blackout 1/8 twist. Anyone here shoot some of the lighter bullets in a 1/9 twist?

I could see where it would be neither fish nor fowl but I get good groups out of my .223 1/7 twist with light 55gr so why not go with the 1/9 twist in a 308? It should shoot good enough with 150s and still shoot the heavies and maybe some sub sonic stuff also. I've searched and can't really find much on a 308 winchester with a 1/9 twist. Plan on a cut-rifled varmint contour 24". Seems like it might be interesting.

For long range/ELR shooting and some very specific projectiles, over spinning can be a problem. Another aspect of relatively fast twist is the tendency to come out a bit short in the MV department compared to slower twist barrels. There's math for this but I won't bore you or embarrass myself by quoting it.

That said, it seems like your intended purposes will be well met by such a barrel. I have three such barrels myself for the express purpose of running 175 to 230 grain including the 180 grain Warner FTR bullet. I suppose I could run 150s in it but I'd be inclined to choose a heavily constructed bullet fired within a reasonable distance. The nice thing is that I have a honey of a subsonic load as well as what might be best described as a short range urban interdiction load that stabilize very very well and dont work the suppressor too hard.

Hit me up if you want to chat more directly.

 

[epeet]

I have a 1:8 twist on a 308 work gun. It will put 5 rounds of 168 FGMM into .9 - 1.3 inch groups. It shoots 175s about the same. It shoots some bonded hunting type bullets into shotgun patterns, but it will shoot Federal 168 Tipped Bonded into the same POI and group size as the 168 FGMM. It replaced a 1:12 that put 168 FGMM into 5 round groups of .4 - .6.

So, my take is that the barrel does well with quality ammo, but is ridiculously over-twisted for certain types of bullet construction, especially bullets that may not be bonded completely concentrically.

Now, starting about 400 yards +, each 100 yards you have to add .1 or .2 mil wind correction to make up for the spin drift. Spotters can see the bullet arc in flight. I would expect it to shoot relatively well with 200 or 220 grain match rounds, but to some degree, I see little point trying to make that work in a 308 as your starting velocity is so low. I think that 1:10 is a good sweet spot for 308 and that 1:8 is way too fast. There is an argument that the bullet should be more stable when transiting the transonic threshold if spun faster. I think the extra math and wind correction isn't worth my ability to apply 9mm ballistics at 750 or 800 yards, and I hate the tradeoff in poor performance with certain bullet types that otherwise shoot great in 1:10 or 1:12. Fast twist makes sense on modern cartridges designed for long/efficient bullets like you see with the Creedmoor line, but that isn't a .308, and really can't be a .308, unless we are willing to jump the PSI by 10k+. Not sure if this yelps. I think a lot of people want 308 to be a 300 WinMag or 6.5 Creed.

So my take is - if you want to configure a .308 to shine with a fast twist, is your use case actually better handled by another cartridge? Or do you just want to have a fun project gun - then rock on and please post back here with what you come up with.

 

[OLD308]

I shoot 308 Win in 1-12, 1-11.25, 1-10, and 1-8. M-852 reamer.
If you reload, no problem.
If not the 1-8 get a little touchy with factory match loads. For hunting and dynamic shooting no issue, you can’t hold the difference. For paper punching prone, yea there is a difference. Still, FGMM holds sub MOA at 500 in the 02 1-8 twist I have.
150 Lehigh MS
160 Warner Flatlines
155 Palma of ever brand
168 SMK
176 SMK
Every powder and primer combination know to man. If your not a speed freak, you will easily find a sub MOA load with any of the above and more.
It’s a 308 win, don’t over think it
They don’t call it “God’s Cartridge” for nothing!
Hope this helps.

 

[Slowroll]

I have been running a 18” 1/8 benchmark chambered by LRI. It has been sub moa for me with many different factory loads. It regularly goes 5/5 at 500 on a 12” plate with me, the kids, or the wife behind it. With 168’s it runs 2530 fps. I think the shorter the barrel is. the more forgiving the fast twist is, purely speculation on my part. I agree with OLD308, for hunting or steel it just works. Good luck.