Twist rate for 308

[tomhenry]

I'm shopping for a bolt action rifle for medium to medium heavy game. I was looking at the 243 but think I like the 308 better.

1 in 10 twist would handle the heavier bullets best and would allow me to load the cartridges to the rifling.

But the rifle I'm considering is the Left Handed Tikka stainless lite, and it's only offered in a 1 in 11 twist.

Significance?

 

[RdrBill]

Sir.
You can open a big can of worms and discussson on this issue. From the internet:

"Gunsmiths generally use the Greenhill Formula to determine the optimal twist for a given bullet. The formula is T=150(d/r) for velocities from about 1500 to 2800 fps. Substitute 180 for the 150 value for velocities exceeding 2800 fps. "T" is the twist rate. "d" is the bullet diameter. "r" is the bullet length to diameter ratio (length of bullet divided by diameter). In .308, it works out fairly well. Sierra 168 grain Matchking is 0.308 inches in diameter. Bullet length is about 1.210 inches so we have a length to diameter ratio of 3.929. Plugging this value into the formula and using the 150 constant (the proven best velocity for the 168 grain MK is 2550 - 2600 fps), we get T=150 x (.308/3.929); T=150 x 0.078; T=11.76 inches or 11 3/4 inch twist …. One rotation of the bullet for every 11.76 inches of barrel traveled. This is very, very close to the "standard" 12 twist barrels on our PSS's and on my Chandler and one of the reasons they shoot the 168s so well. The 175 Matchkings do not perform as well in the 12 twist barrels. Again diameter is 0.308 inches. Bullet length is 1.257 inches, resulting in an ld ratio of 4.081. … plugging into formula (optimal velocity is 2500 to 2550 fps so we will use the 150 constant again) T = 150 x (.308/4.081); T = 150 x 0.0755; T = 11.320."


"and also some recommendations:
Berger Bullets, says, on their web sight...
.308 CAL 155gr Very Low Drag Recommended twist rate is 1/14
.308 CAL 168gr Very Low Drag Recommended twist rate is 1/13
.308 CAL 175gr Very Low Drag Recommended twist rate is 1/13
.308 CAL 185gr Very Low Drag Recommended twist rate is 1/12
.308 CAL 190gr Very Low Drag Recommended twist rate is 1/12
.308 CAL 210gr Very Low Drag Recommended twist rate is 1/11"

"In Champions Choice catalog they mentioned stocking 1:11 twist Kreiger's for people who can not make up their mind. Sounds like a reasonable solution to me."



net info to be gained is that heavier bullets need a faster twist rate.
1 in 10 is near the optimum for big , big .308 bullets. A slower twist rate would be better suited to more reasonable bullet weights.
Bill@Yuma

 

[Ron H.]

I'm shopping for a bolt action rifle for medium to medium heavy game. I was looking at the 243 but think I like the 308 better.

1 in 10 twist would handle the heavier bullets best and would allow me to load the cartridges to the rifling.

But the rifle I'm considering is the Left Handed Tikka stainless lite, and it's only offered in a 1 in 11 twist.

Significance?

Sir, it kind of depends on what you regard as heavy. FWIW, the 1:11 barrels on my heavy match .308 Garands are very accurate with 168s and 175s out to 600 yards. I imagine you might run into stability problems with 190s or heavier, but haven't tried this, so don't know for sure.

Hope this helps, and Semper Fi.

Ron H.