[viking499]

I have seen where 223's have various twists. 1:8, 1:9 and 1:12

What twist is suited for what grain bullets? What is the range and "sweet spot" for each of the twists listed above?

[Robert]

55-69gr will work just fine in 1:7, 1:8, or 1:9. Heavier bullets, 69gr and up, work better in a 1:8 or 1:7 twist. Super light varmint rounds, 30, 40 and low 50 gr bullets, will work better in a slower twist like the 1:12.

Now of course this is just a general rule of thumb. One 1:9 may shoot real light bullets just fine while another does not.

[ApplePie]

I had a 1:9 twist Savage that was the most accurate with 52-grain Speer Hollow Points. Didn't like 40 grainers as much.

[mjsdwash]

i occasionally see 55gr full power loads disintegrate from my 1 in 7 20" at about 75 yards, only with handloads though. The same loads makes it to the 100 yard line fine through a 1 in 9.

[tactikel]

All the above is right on. You can find many tables that recommend bullet weight ranges for a specific twist. Keep in mind that stabilizing a bullet is a function of bullet LENGTH vs velocity and twist. Bullets with polymer noses and boat tails will be longer and harder to stabilize than a flat base lead bullet. Copper bullets really change the game. .223 barrels in 1:9 to 1:12 ranges will handle most needs, and commonly used bullet weights.

[gotigers]

Robert and Tactikel are both spot on. It is bullet length. However, bullet weight is easier to quantify for us consumers. My 1:9 likes 50gr to 62gr. My 2 1:8s likes 55gr to 70gr. I haven't tried over 70, but i think up to the common 77gr would do fine with my 1:8s. I don't own a 1:7. I have shot several ARs with 1:7. They have shot any weight fed to them.

In 3 gun, I shoot a lot of 55gr bulk at close targets to save money. Then i shoot 70gr for intermidiate distances out to 300 yards. Most of the bulk ammo is FMJ and the better stuff is BTHPs and some SMK. For the intermidiate ranges i like the Hornady steel match. The 1:8's handle all of those.

[carbine85]

The longer the bullet = faster twist rate.
Most target rifles use the 1:8 and a heavier 69 gr bullet.
For accuracy purposes or target shooting the 1:7 won't shoot the lighter bullets as well as the 1:9. I am talking about normal ranger distances of 100 - 300 yards.

[oldpapps]

Twist formula

Just copy this and paste it into a spread sheet (block C1 is a good option).

=(30*+C5)/((+C7/+C4)^2*+C4^3*+C6/+C4*(1+(+C6/+C4)^2))*(+C8/2800)^(1/3)*((+C9+460)/(59+460)*29.92/+C10)

Then copy and paste this (to make it simple, put the 'Where' in block E2).

Where:
Sg - is the stability coefficient and should not be less than 1.4, but more is ok
C4 - Caliber in inches (.223 for both .222 and .223)
C5 - Bullet Weight in grains
C6 - Bullet Length in inches
C7 - Barrel Twist in inches per turn
C8 - Muzzle Velocity in fps
C9 - Temperature in degrees F (59F normally used)
C10 - Pressure in inches of mercury (29.92 normally used)


This will put the variables in the 'C' column from row 4 to 10. The numbers will have to be typed in to the 'C' column. The location that you put the formula will display the final calculation value. Until all of the numbers are entered, it will show and error (#DIV/0!).

It is not that hard.

[tactikel]

Awesome oldpapps!! Just one question, how can one determine the stability coefficient? I have studied bullets for a while and am not familiar with it. Thanks for the formula.
I am convinced the barrel on my .22-250 is haunted, it hates polymer tipped bullets, boat tails, and hollow points. All shoot 1.5 MOA. 45 gr flat based spire points shoot 0.5 MOA. I hope this formula will help me to understand this barrel.

[helotaxi]

That's the formula for the Miller Stability Index. Sg is what is output by that formula. 1.4 isn't the minimum value that is stable but is the generally accepted value that is immediately stable rather than a bullet that has to "go to sleep" at some point downrange.

[carbine85]

I sometimes use this web site http://kwk.us/twist.html