Twist rate and Bullet weight

[vladimir]

Being new to reloading .223 rem, please educate me on bullet weight and twist rate. I have two rifles for which I will be reloading – a 1/7 and a 1/9 twist, both are semi-auto.
For starters, I’ve been told various and often conflicting things from well meaning individuals. For instance:

1. “Bullet weight doesn’t matter, it’s all about bullet shape – the longer the bullet the faster twist you need”.
2. “Bullet shape doesn’t matter – heavy bullets are for fast twist”.
3. “Put a bullet under 60 grains in that 1/7 and it’ll fly apart in flight”.
4. “Put a bullet over 60 grains in that 1/9 and it’ll just tumble all over”.
5. “ You can shoot all weights and shapes regardless of twist rate – just some will be more accurate than others.
And my personal favorite – “what’s a twist rate, never heard of it. I just throw some powder and some lead together and let er’ rip”.


Anyway, as you can see, not everything you are told is helpful. My goal is to work up a accurate loads for each rifle. As opposed to just starting someplace, I thought I’d check with those who have experience and maybe learn something constructive. If you have thoughts about correct twist vs. bullet weight/shape please let me know.

Thanks in advance.

Vlad

 

[Vern Humphrey]

1. “Bullet weight doesn’t matter, it’s all about bullet shape – the longer the bullet the faster twist you need”.

Correct -- it is bullet length that dictates needed twist. The classic Greenhill Forumla is Bullet Diameter ^2 X 150/Bullet Length (all in inches). This gives you the needed twist in inches per revolution.

A .223 bullet an inch long would require a 1 in 7 twist.

2. “Bullet shape doesn’t matter – heavy bullets are for fast twist”.

A common misconception -- because longer bullets tend to be heavier.

3. “Put a bullet under 60 grains in that 1/7 and it’ll fly apart in flight”.

That depends. A fast twist stresses the bullet jacket. High velocity adds to the stress. At some point the combination of higher velocity (due to less bullet mass) and faster twist will break up the bullet -- but you should shoot the rifle first, before taking someone's rule-of-thumb as gospel.

4. “Put a bullet over 60 grains in that 1/9 and it’ll just tumble all over”.

Again, maybe yes, maybe no. Invest in a box of bullets you are interested in and "ask the gun."

5. “ You can shoot all weights and shapes regardless of twist rate – just some will be more accurate than others.

Not true -- at least in the .223. Some other cartridges suffer from the same problem - for example the .250 Savage generally shoots better with shorter, lighter bullets, as does the .244 Remington. Old metric calibers (and the .30-06) on the other hand, were designed for long, heavy bullets and will shoot about any weight and length well.

And my personal favorite – “what’s a twist rate, never heard of it. I just throw some powder and some lead together and let er’ rip”.

Don't stand near this guy on the firing line.

 

[RustyFN]

Normally a 1:9 will shoot up to around 75 grain bullets accurate. If you want to shoot larger than that go to a 1:7. If you are just plinking or shooting competition up to 300 yards a 1:9 would be fine. If you want to get out to 600 yards plus I would go with the 1:7 and a heavy bullet.
Rusty