Optimum bbl twist for 175g in 308Win

[jpretle]

What say ye???? 10twist???

 

[stool]

all depends on bullet length, not weight, so what bullet ?

 

[MrMajestic]

http://www.bergerbullets.com/products/target-bullets/

 

[spclark]

1:10 is likely overkill for many 175's unless you shoot in arctic conditions. 1:13 will stabilize some. Were I spec'ing a new barrel for 175's, it'd be 30" finished & more than likely a 1:11.

 

[1shot]

SPClark is correct. I run 175-185 in a 11.25 twist at 30" finished with no problems.
I hope this helps,
Lloyd

 

[Dgd6mm]

I had a 30" Criterion 1-11 twist chambered and it shoots 175 -185's real well to 1000 yards. This is a button rifled barrel and I have not checked the exact twist, more then likely it is a little slower twist, this is the norm for button rifled barrels.

 

[wwbrown]

I think they did a lot of testing trying to find the optimal twist rate for 175 grain SMK from a 308 at Aberdeen Proving Grounds. After lots of rounds fired and some tax money burnt they found the optimal twist rate was 11.27 inches.

 

[gsg5pk]

Depend on you heaviest plan for projectile.

If 175gr was the heaviest projectile for your choice, I would suggest 11.25

But I would prefer faster twist like 1:10 which suitable for modern design with longer and heavier projectile.

 

[jpretle]

Thanks all for your input. Advice for 11 plus twist, taken.

 

[Medic505]

I have an old Rock Creek barrel that is 11.27 and it shoots 175 Berger LRBT's like a laser. It also shot 185's both jugs and hybrids well too. I wish I had ordered
three of them when I got the one!

 

[gsg5pk]

Some had prove that 1:10" also can shoot 155gr


So, nothing worried about 175gr

 

[akajun]

1-12 was the standard for the 175 matchking when the m14 ruled the roost in Highpower. Mine shoots them very well, but will also shoot the 135smk's and other lighter bullets I shoot on the short line as well.

 

[Laurie]

As Stool says. the bullet length is the critical factor in its relationship to the calibre. All .30 175s will stabilise with a 1 in 13-inch twist, but most are better served by 1 in 12-inches. The 175gn Sierra MK is a bit shorter than the same weight Bergers and has a near optimal rate at 1 in 13.

The newish 175gn Berger Tactical OTM was designed by Bryan Litz for minimal transonic disruption and transfer to subsonic flight from milspec rifles with the recently adopted 1-11.25" twist rate and MVs in the 2,650 - 2,800 fps range. Such a bullet fired from a .308 / 7.62mm cartridge is usually transonic a bit short of the 1,000 yards mark, or even subsonic depending on the bullet and barrel length / MV, and in many cases this increases both air-drag, sensitivity to wind changes and group dispersion. The US Army proved this with the old 173gn FMJBT Frankford Arsenal match bullet as loaded in .30-06 and early .308 Win match ammo in tests many years ago. The key retained velocity was 1,226 fps, ie 100 fps above the sound barrier under normal ballistic conditions.

Since then, 175gn bullet stability under these conditions has improved and the 175gn Sierra MK and 11.25" twist rate is pretty good, but the Berger / Litz design is intended to improve it still further.

So .......... it comes back to bullet model, barrel length / MV, and distance to be shot over.

 

[dcnyli]

I run 1-11, 24" and it hammers with 175s all day.

 

[chevytruck_83]

Faster twists will stabilize a bullet better once it drops below the speed of sound. Is there any real reason faster isnt better? I recently read an article that said modern bullet jackets will handle the faster gyroscopic forces just fine and increased pressures due to faster twists are insignificant.

 

[stool]

i would answer that GENERAL statement with a general answer..no...
way too many factors for it to be true in all cases.
generically bbls and rifling are better today.
but jacket thickness is very important
look at what happened when people started pushing 180 gr 7mm bergers....berger had to come out with a heavy jacket to take the load.

so no..and i would not build a rifle on that statement.

Faster twists will stabilize a bullet better once it drops below the speed of sound. Is there any real reason faster isnt better? I recently read an article that said modern bullet jackets will handle the faster gyroscopic forces just fine and increased pressures due to faster twists are insignificant.

 

[XTR]

Different people have had different results, but the one time I tried 155s [SMK 2156] in a 1:10 barrel I couldn't get it to shoot them. Just the barrel or the twist? I don't know. If I was never planning to shoot anything heavier than a 185 (and if you don't shoot F-TR why would you) then I'd get a 1:12 or a 1:11.25 twist.