bullets and twist rate

What's the bullet length and diameter? Is it jacketed or cast bullet? It is not the weight that matters. There would be more determining factors if you are shooting cast bullets.

-TL
 
I am going to guess you are talking about .223 Remington.

55 gr bullets will not stabilize in 223s with 16" twist.
50 gr bullets will stabilize in 223s with 16" twist.

Many 223s single shot are 12" twist and have no problem with 55 gr or 62 gr.

The 1 in 8" twist is for some of those 75 gr bullets.
The 1 in 7" twist is for all of those 75 gr bullets.

The problem is not the weight as much as the length of the bullet, but everyone knows the weight... so we talk about the weight.
 
An 8 twist is a good compromise that should shoot well with everything except the for bullets on both ends of the spectrum. I'd not expect any issues with anything 50-69 gr. Heavier or lighter might not give optimal accuracy, but I'd bet they ain't bad either.
 
The barrel is a 20" barrel on a AR-15. The barrel has a 1:8 twist. I have a bunch of the Hornady 55gr SP bullets I was thinking about loading for it. They are around .7" long. I also have some nosler ballistic varmint tip which are 50gr and .79" long.
 
140 AMAX works pretty well through mine, although I think it is fast enough for the 160s. You are talking 6.5mm, right?
 
I go by Greenhill's equation for twist rate

T=150*c^2/L

T is twist rate in inch/rev;
c is bullet diameter in inch;
L is bullet length in inch.

L=0.7", c=0.224", T=10.8"
L=0.79", c=0.224", T=9.5"

Twist rate of 8" should have no problem stabilizing both bullets.

-TL

kuca_2004 said:
The barrel is a 20" barrel on a AR-15. The barrel has a 1:8 twist. I have a bunch of the Hornady 55gr SP bullets I was thinking about loading for it. They are around .7" long. I also have some nosler ballistic varmint tip which are 50gr and .79" long.
Click to expand...
 
"Should" is the key word here. Sometimes I have gone up to heavy, long bullets to help out a poor performing rifle and it usually helps. Every once and a while I would load the same bullets in two different cartridge chambered guns and the results would be terrible in the one rifle. The poor shooting one would usually be of a higher velocity with the same twist rate. Same bullet, same length. I have often wondered if velocity did not play a major part in the stability of certain bullets. Generally you drop the velocity when you step up the bullet weight. Think about how many times you made a good grouping rifle shoot bad just by loading it really hot. Just an observation over the years.
 
Stabilization here means not tumbling. Accuracy is more than that. But there won't be any accuracy if the bullet is tumbling.

-TL
 
Stabilization means what it says, be it tumbling, wobbling, or spin drift. How would you check to see if a ball was tumbling? There is a big difference between a musket and rifled muzzle loader.
 
It was an example. I have no idea what you are talking about. Stabilizing a bullet does not mean to stop it from tumbling. I had a .244 barrel I used as a 6MM. This set up is well known for not stabilizing heavier bullets. You may have to play around with the load to get one to shoot decently, but I have never had a bullet tumble with it.
 
My stag has a 1:8 and shoots Sierra 1390 (55 gr hp) the best of everything I have tried. Which ranged from 52gr-69gr
 
"Stability
Calculates the Miller stability factor. This formula was derived by Don Miller and published in Precision Shooting. This formula is much better than the antiquated Greenhill's formula. Stability value should be in the range of 1.3 to 2.0 to ensure bullet stability. Don Miller and Dave Brennan (editor of Precision Shooting) have also been kind enough to let me host his stability paper on my exterior ballistics bibliograpy page. The paper is titled A New Rule for Estimating Rifling Twist An Aid to Choosing Bullets and Rifles."

Calculator available here (free), and also they have lengths for most bullets:
http://jbmballistics.com/ballistics/calculators/calculators.shtml
I have used the calculator and it successfully predicted I could shoot Hor 75 gr OTM BT in a 1:9" Savage. 1:8 is great for heavy bullets. I think the calculator is a better guide than the table below.
Also read the twist section here:
http://www.accurateshooter.com/cartridge-guides/223rem/
"Barrel Twist Rate 1:14″ 1:12″ 1:9″ 1:8″ 1:7″ or 1:6.5″
Max Bullet Weight 55gr FB 65gr FB 73gr BT 80gr BT 90gr BT VLD"
 
I took notice that muzzle velocity is included. There is a disclaimer at the top. Probably because all these formulas are basic charts to choose a barrel blank to start with. As with all "Book" information, they are guidelines, not absolute fact.
 
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