twist and barrel

[rolly]

Could someone explain the pros and cons of twist values for .308.

I see online most stock .308 with a twist of 12, but i also see twist variation from 8 to 14 for custom barrels.

Please advise.

[GJC]

What do you plan on using the rifle for? That would help out alot.

[rolly]

What do you plan on using the rifle for? That would help out alot.

Hi,

It does not matter how i am planning to use the rifle. I just want to understand how twist works and its implication with barrel and ammo so i can do an educated purchase when i will buy a new barrel or new ammo or reload new ammo, or build multiple rifles for different purpose.

Cheers

[Iloveguns]

Hi,

It does not matter how i am planning to use the rifle. I just want to understand how twist works and its implication with barrel and ammo so i can do an educated purchase when i will buy a new barrel or new ammo or reload new ammo, or build multiple rifles for different purpose.

Cheers

Faster twist is for heavier bullets. Slower twist for lighter bullets. Smaller number, faster twist. Depending what you want to use the rifle for is what will determine what twist you want.

[GSF44Mag]

Faster twists will help to stable heavier/longer bullets. Thus the problem for many that are in the non lead areas. Due to the length of the non lead projectile, many of todays rifles do not have the proper twist to stabilize them. The twist rate is usually too slow.

[rolly]

Thanks guys, is there a chart for optimal twist according to barrel lenght and bullet weight ?

[MongooseV8]

For a 308 a 1:10 is a standard twist these days. That will stabilize pretty much any bullet weight. 1:10 is one full revolution of rifling twist every 10 inches, so a 1:12 would be a slower twist rate. Some people will tell you to only shoot heavy bullets in a fast twist barrel for accuracy reasons but that is a myth. Actual twist rates will depend on the caliber and the cartridge.

[milotrain]

There is no "chart" there is a ballistic stability formula, and on berger's site there is a calculator. You find out what bullet you want to run then you find out what twist rate you need to run it. That's why it matters what you want to do with it.

In the case of the .308 there are sort of two standards. The 1:10 which allows for heavier bullets, and the 1:13 which is optimal for the 155 palma bullet. With the limited case capacity of the .308 you use seating depth to control powder volume and the ability to run a heavy bullet, which means you need to throat the chamber for said heavy bullet. The chamber you can use to optimally run a 155 palma bullet will not run a 190 HPBT optimally.

If you run the calculator you find that a 1:10 is a bit fast for anything but the longest solid copper/brass bullets. Figure out what you want to shoot, figure out what bullet works for that kind of shooting, buy a barrel with a twist that is optimal for the bullet, and chamber the barrel accordingly. In general the most accuracy will be found with the slowest twist you can run.

[MongooseV8]

If you run the calculator you find that a 1:10 is a bit fast for anything but the longest solid copper/brass bullets. Figure out what you want to shoot, figure out what bullet works for that kind of shooting, buy a barrel with a twist that is optimal for the bullet, and chamber the barrel accordingly. In general the most accuracy will be found with the slowest twist you can run.

Not trying to argue but this has been proven over and over again to be a myth. All you need is a twist fast enough to stabilize the weight you want to shoot. You can shoot light weight bullets in a fast twist barrel with the same or better accuracy.

You cant over stabilize. Case in point varmint hunters like myself like to shoot super high velocity with really fast twist rates with light weight thin skinned varmint bullets. The extra velocity and extra rpm really blows apart little critters, ensuring clean dispatching and no wounded squirrels. I have several varmint rigs and have built dozens for friends over the years, all have fast for caliber twists and its normal to shoot 0.25 moa.

308, 30-06, 300 Win Mag ect, are all easy choices. Go with a 1:10 twist.

[ExtremeX]

Thanks guys, is there a chart for optimal twist according to barrel lenght and bullet weight ?

Too many variables for a chart... use the stability calculator to give you a better simulation of what to expect.

http://www.bergerbullets.com/litz/TwistRuleAlt.php

bullet weight, diameter, bullet LENGTH, velocity, and twist rate are all factors when dealing with gyroscopic stability.

In theory you can stabilize any bullet if you can shoot it fast enough, but that doesn't always work in the real world. Play with the calc to give you an idea of what to expect.

A real world example is my 1:9 twist rifle can stabilize a Prvi or Hornady 75gr BTHP just fine, but it doesn't stabilize the 75gr AMAX very well. Both bullets weigh the same, but one is much longer, nor can a achieve a velocity fast enough to make it work.

[milotrain]

Not trying to argue but this has been proven over and over again to be a myth.

[milotrain]

A real world example is my 1:9 twist rifle can stabilize a Prvi or Hornady 75gr BTHP just fine, but it doesn't stabilize the 75gr AMAX very well. Both bullets weigh the same, but one is much longer, nor can a achieve a velocity fast enough to make it work.

Try the 77gr Nosler, it will stabilize in that 1:9 as well. It's about the length of the 75gr Hornady HPBT but it's heavier so it actually stabilizes at slower RPMs.

[Vu 308]

11.25 5R for a 308win launching 175s

[Fjold]

If all things were equal, a slower twist barrel will give you higher velocity than a faster twist barrel using the same bullet. It takes more energy to convert the forward motion of the bullet into twist at a faster rate. For every action there is an equal and opposite reaction. The rotational energy has to come from somewhere, it comes from the kinetic energy (velocity) of the bullet.

Palma shooters use the slowest twist that will stabilize the 155 grain bullet to maximize the velocity of the bullet when it leaves the barrel.

[Divernhunter]

Just a side note. Varmint shooters use thin jacketed bullets for 1) fast expansion 2) reduce bullets flying off in every direction when hitting hard ground etc.

We like to see squirrels explode when hit. That is why I use a Hornady SX (super explosive) bullets that use extremely thin jackets.

The thin jackets may or may not help accuracy but that is not the main reason for them on varmint bullets