9.3 twist rates

[sambarhunter]

the 9.3 x 64m twist rate I`m advised in my LW barrel is 1:14 and my mate now advises that using a 232 grain Norma Oryx with that twist @2900 fps isn't going to be any ******* good!
Anyone care to advise me?
I want to use the 232`s rather than the 285`s

 

[stug]

Nah, you should be fine. I used JBM ballistic calculator and it came up stable, but I don't know the length of the projectile and used 1.5"

 

[sambarhunter]

I dont have any at hand to measure one but 1.5 inches,that sounds too long to me.

Had a though and I just measured an 285 gr Oryx @ 31.5mm = 1.240157 in inches

Dont know how that helps in ID the 232 gr length.

 

[JET216]

Nah, you should be fine. I used JBM ballistic calculator and it came up stable, but I don't know the length of the projectile and used 1.5"

When I shot a 225 grain Star bullet in my 9.3x64 the velocity was well over 3000 FPS and wasn't stable for sure. A 9.3 bullet that light will not be 1.5" long. Not sure what my twist rate is.

 

[stug]

I dont have any at hand to measure one but 1.5 inches,that sounds too long to me.

Had a though and I just measured an 285 gr Oryx @ 31.5mm = 1.240157 in inches

Dont know how that helps in ID the 232 gr length.

Shorter will make it more stable.

 

[sambarhunter]

1.040 inches for the 232 grs I am reliably told,can you extrapolate on that at all?
I am the dunce with any of this stuff and appreciate all input.

 

[stug]

JBM ballistics stability factor is 3.807. Anything over 1.5 is good.

Just google JBM stability calculator and put the data is.

 

[JET216]

I may be all washed up but once again I think you would be hard pressed to find a 232 grs in 9.3 over 1.5" and I think you would need the length to stabilize.

 

[Mekaniks]

To figure out the optimum twist rate for the bullets you want to shoot use this easy formula-

Bullet Diameter squared x 150. Then divide that total by the bullet length. This will equal the optimism twist rate in inches.

 

[sambarhunter]

Ok that`s like i:20 something.

So in effect some say the 232 are ok others are suggesting that they are not or I at least need a far different twist rate?
My head spins

 

[JET216]

Why do you want to shoot 232grs? What are you hunting and what range and conditions?

 

[sambarhunter]

Large deer species (sambar) from 50 up to 300-400 yards ,winter hunting in hill country.
I just wanted the flatter option than the 285`s

 

[JET216]

How about 250 grs.? I have great success with them, Barnes "x". Am currently working on a load for 250 grs. Cutting Edge bullets and can put the Ballistic Tip on for reaching out there.

 

[Mekaniks]

Ok that`s like i:20 something.

So in effect some say the 232 are ok others are suggesting that they are not or I at least need a far different twist rate?
My head spins

Based on .366 dia bullet that is 1.240 length, a 1-16 twist would be optimal

 

[sambarhunter]

1.040 inches for the 232 grs is the bullet length Mek.

Jet the 250`s would be ok of course but not quite as flat like the lesser weights.

 

[sgt_zim]

The Norma 232 gr bullets have REALLY low BCs - less than 0.3. They come out blazing fast, but for longer shots, you're going to lose velocity fast and end up dealing with roughly the same hold over as you do for the heavy bullets. IIRC, Nosler AB 250 gr has a BC just south of 0.5. That'll be your flattest option out of all the .366 bullets available, at least as far as I am aware. 2nd highest BC that I know of in .366 bullets is Nosler Partition, at .482 or something close to that.

Assuming a MV of 2700 fps for 9.3x64, that gets you out to 500 yards before you fall below the 1800 fps threshold Nosler says is the lowest you want for impact velocity.

 

[sambarhunter]

Sarge,I like what you say,thank you.

 

[AZDAVE]

1 in 14 in a 9.3 will stabilize all bullet weights fro 232-320gr. You will be good to go. The 250 gr nosler will shoot flatter than the 232's. at longer ranges.

 

[sambarhunter]

That also makes me feel better AZDave as my LGS have told me that my 232 gr order has come in!

 

[Graham Hunter]

I think you will find the 250gr. Nosler AB will work better for all ranges than the 232.