1 in 10 twist in .308

Is the 1-10 barrel designed for a particular weight bullet, or is it just being used by default? 1-10 in .30 barrels has been used since the 1890s.
It will certainly work with any bullet you'd shoot in a .308, to 200 grains.
 
Last edited:
John Whidden was tops in previous USA trials for the Palma team shooting 155 bullets with 10T .308 Win. Go quicker but not slower.

Regards,

Peter
 
hometownhero said:
Don't they have to use those bullets for palma?
Click to expand...

Yes, but the point is that a faster twist will still shoot lighter bullets just fine. For a long time 1:13 was the most common for 155's, now many are moving to 1:12, some faster. I have a 1:10 on my TR rifle, it'll be years before I can shoot TR as good as it can.
 
I remember reading an article years ago where the author claimed his most accurate .308 Win rifles had a 1:12 twist rate.

I have no clue as to what bullet weights he was using though, or what ranges he was shooting at.
 
As far as I know, twist rates just stabilize a bullet, or not. Using a 'fast' twist rate like 1:10 can cause bullet failures in 'light' for caliber bullets. Varmint bullets, or other thin-jacketed bullets, for example, are designed to perform at a level on impact. Jacket separation occurs as your prolonged shot string increases the heat in the chamber. A heated thin-jacketed bullet can fail, and come apart thus turning your rifle into a shotgun of sorts. Spinning a projectile causes friction, which causes heat, which causes blow-ups; in addition to prolonged shooting conditions. The below is from the berger bullets website:

"For example, the very popular 6.5mm 140 gr VLD is available from both the Target line and the Hunting line. The bullet sold in the Target line has a thicker jacket design to eliminate or significantly reduce bullet failures (blow ups). Bullet failures typically result from a core melting during high shot counts in a short period of time (match conditions). The same 6.5mm 140 gr VLD sold in our Hunting line is made with the standard thickness jackets that are proving to be extremely effective for initial penetration and lethal internal expansion on game. Hunters’ low shot counts over longer periods of time produce a very small chance of bullet failure" (para 4, 5). http://www.bergerbullets.com/berger-line-split/

So, unless you are going to dedicate your rig to varminting or other applications where you rack up prolonged shot strings using thin-jacketed bullets, you will be fine with a 1:10 twist. If you just want to use a light for caliber bullet to hunt, again, you'll be fine with the 1:10 twist, as long as you don't machine-gun the animal... lol
 
I went to one of those LR courses put on by Accuracy 1rst and the instructor talked about some of the testing they did on faster twists and the benefits at longer ranges. They way he explained it made sense and they said their testing showed that a faster twist extended the ranges at which the groups started opening up as the rounds slowed down and neared trans sonic. I’d never considered this but it seemed to make sense:

Twist sets up a certain rotational speed (RPM’s) that is separate from velocity (FPS) So as the bullets rotational speed decreases it slows to a point where it starts to come out of its spin and the tip will start to yaw and wobble-think of watching a football start to slow down and wobble in flight or a top slowing down. As it wobbles and yaws think of what happens to the flight path and the cone shaped group size that bullet now will fall into. This is the point where the groups start to open up down range.

So start the bullet out spinning a little faster ( rate of twist) and the wobble point gets pushed a little farther down range. This was especially helpful in increasing the range of subsonic ammunition too but worked on all rifle ammunition. Not necessarily any outright accuracy benefit at close range but helped keeps the groups from opening up down range as the bullets neared what was previously considered maximum range at the slower twist rate. Now apparently the USMC is going to a 10 twist in their M40A7 vs the 12 twist they have used since the 70’s in 308’s.

So in short 1:10 twist in a 308 for sure in any standard weight bullet.
 
njohnson said:
I went to one of those LR courses put on by Accuracy 1rst and the instructor talked about some of the testing they did on faster twists and the benefits at longer ranges. They way he explained it made sense and they said their testing showed that a faster twist extended the ranges at which the groups started opening up as the rounds slowed down and neared trans sonic. I’d never considered this but it seemed to make sense:

Twist sets up a certain rotational speed (RPM’s) that is separate from velocity (FPS) So as the bullets rotational speed decreases it slows to a point where it starts to come out of its spin and the tip will start to yaw and wobble-think of watching a football start to slow down and wobble in flight or a top slowing down. As it wobbles and yaws think of what happens to the flight path and the cone shaped group size that bullet now will fall into. This is the point where the groups start to open up down range.

So start the bullet out spinning a little faster ( rate of twist) and the wobble point gets pushed a little farther down range. This was especially helpful in increasing the range of subsonic ammunition too but worked on all rifle ammunition. Not necessarily any outright accuracy benefit at close range but helped keeps the groups from opening up down range as the bullets neared what was previously considered maximum range at the slower twist rate. Now apparently the USMC is going to a 10 twist in their M40A7 vs the 12 twist they have used since the 70’s in 308’s.

So in short 1:10 twist in a 308 for sure in any standard weight bullet.
Click to expand...

Yes, no, kind of... The issues get extremely complicated as we are dealing with dynamic and static stability... also, supersonic and transonic stability/design.

Over spinning (to a degree) can help improve its BC slightly. This I have proven at LR. But it does increase the aerodynamic jump substantially SO.... pick your poison.

Transonic stability is not necessarily tied to the spin rate. That is baked into the bullet shape.

Every bullet shape has an ideal RPM to stabilise.. once established, the spin induced stability actually INCREASES as the bullet velocity decays.

however, not every shape is designed to go transonic and then subsonic. The wobble that some bullets exhibit is very real and that is tied to the bullet shape. Some are even sensitive at high speeds.

Current bullet designs push to longer/pointier shapes for the given bullet mass so you cannot go by bullet weight to determine what twist it needs. A 30cal 200gr RN needs very little spin... the newest high BC 200gr critter may need way more then common barrels use. I have and sell 8 twist 30cal barrels for a reason.

YMMV

Jerry
 
Spin slows very little compared to velocity. Some bullets, such as Sierra .30 168 go wonky at transonic, others transition just fine. As mentioned, trend is to go quicker twist.

Regards,

Peter
 
Would Barrel length come into play at all when using the heavy bullets with a 1:10 twist? I have the 16.5" rem 700 in mind when I ask this question. For example does a longer barrel have more time / rotations to effect the heavy bullets?
 
spenom said:
Would Barrel length come into play at all when using the heavy bullets with a 1:10 twist? I have the 16.5" rem 700 in mind when I ask this question. For example does a longer barrel have more time / rotations to effect the heavy bullets?
Click to expand...

There are 1911 pistols with 4" barrels that spin 230gr bullets just fine. Your 10 in a 700 with short barrel will not have a problem stabilizing heavy. Speed will suffer though.
 
Looking for test loads or ideas for new-to-me FNAR+ Hogstalker.

My Hogstalker seems to like 150gr Sako SuperHammerhead.

I am sure they both have 1 in 10 twist.

Some of the bullets and powder I am considering.

Nosler AB 165, Nosler CT 168 Ballistic SilverTip, Berger 168 VLD, Hornady Eld-X 178.

Powders

Varget , IMR 4064, N-140
 
What I don't understand about rifle twist is why not give every rifle a 1:1 twist and be done with it? You always hear about how a fast twist is needed for heavier (longer) bullets but still shoots the lighter (shorter) ones just fine. Surely there has to be a negative point about a twist too fast?
 
Dake21 said:
What I don't understand about rifle twist is why not give every rifle a 1:1 twist and be done with it? You always hear about how a fast twist is needed for heavier (longer) bullets but still shoots the lighter (shorter) ones just fine. Surely there has to be a negative point about a twist too fast?
Click to expand...

This is what happens when you spin a bullet too fast. Watch approximately 20 yards out from the muzzle. See that little puff of smoke? That WAS the bullet. It is now in very small pieces, none of which made it to the target or anywhere near it.

 
spenom said:
Would Barrel length come into play at all when using the heavy bullets with a 1:10 twist? I have the 16.5" rem 700 in mind when I ask this question. For example does a longer barrel have more time / rotations to effect the heavy bullets?
Click to expand...
Barrel length will affect spin as a function of velocity gain. For an easy example a 1 in 12 will gain 1 rotation per second, or 60 rpm for every fps velocity gain. If you figure 30 fps per inch of barrel you're looking at 1800 rpm for every extra inch of barrel. Not terribly significant when you consider a bullet travelling at 2800 fps would already be at 168000 rpm.
 
You must log in or register to reply here.
Back
Top Bottom