Tell me about twist in a barrel

9

9mm

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So what's the difference in all these Twists for rifles 1:12 1:14 1:16? what others are there?

Which is the best ?
 
which is best depends on to many things. As stated ,what caliber,what wt bullet.
It basically comes down to what your shooting(caliber) and what grn bullet you are going to shoot. example-223's twist rates- 1 in 7 ,,1 in 8, 1 in 9,1 in 12,1 in 14,. heavier bullets like faster twist rates.
 
The right twist depends on the caliber, bullet length, and velocity range.

The twist is equal to 150 x bore diameter^2 divided by the length of the bullet. If the velocity is above 2800 then use 180 instead of 150.

So, a 308 with a 168g would be (150 * .308^2)/1.29 which is 11. Note that is is the length of the bullet and not the weight that is important.
 
Not pickin on ya chasep255.

Generally heaver bullets require faster twists.
Click to expand...

Add because in general heavier bullets are longer.


But is very dependent on Caliber.


Hypothetical view.

A 105g 6mm is 243 in diameter.

What if the same 105g was for a 60mm? It would be very much shorter.
 
What MC223 is trying to say is that the ideal twist is a function of the bullets diameter as a function of its length. For a given diameter, as the length of a bullet increases so does the need for faster twist.
 
OK 223/5.56, now what are you intending to do with it. Hunting coyotes, paper, prairie dogs, deer. What you intend to do with it will determine the best weight bullets and therefore the best twist for your rifle.
 
As the fired bullet moves down the barrel toward the muzzle, if you had a '1 in 10' twist, that means the bullet makes one turn or rotation in every 10 inches of travel down the barrel. A slower twist would be something like a '1 in 12' twist, where the bullet has to travel 2 inches further in the barrel to make that one rotation.
 
To add to what 603Country said, the twist imparts a spin to the bullet that stabilizes its flight. The most common analogy is the visual spin on a football in flight.
 
So wouldn't a higher twist always be better considering that adds stability to a bullet for longer. Or does that make the drift from twist worse in the longer ranges so diminishes the advantages towards stability.
 
No. If you have more twist than is needed, bad things start to happen. In extreme cases, the bullet can actually explode in mid air from too much centrifugal force. A bullet that has a 1/12 twist traveling 3000fps will be spinning 180000 RPM when it leaves the barrel. A light-weight bullet with that much spin will literally spin itself apart.

In less intense situations, you'll decrease accuracy. Not to mention an unnecessary hit to velocity (the more you spin it, the more friction as it goes through the barrel resulting in velocity loss).

Bottom line is that there is a theoretical ideal for twist rate for any given combination caliber/bullet weight. Since barrels cannot magically change their twist as you change loads, manufacturers have to pick an "average" that they think shooters will need. If you really do intend to use a bullet on either end of the weight spectrum for that particular caliber it will be to your benefit to select a manufacturer that produces a barrel that fits your intended bullet.

Case in point is the 30-06. The standard twist for that caliber is 1 in 10". You can get normal 30-06 bullets from somewhere around 140grn all the way up to at least 220grn. That standard 1 in 10" twist is ideal for a 165 to 180grn bullet. It will usually shoot 150's OK. However, if you try to shoot 220grn bullets, you'll probably find less-than-desireable accuracy. 1 in 10" just won't stabilize it well.

Manufacturers USUALLY get it pretty right. Remington has had some pretty ugly failures though. They developed a .244 (6mm) to compete with the .243. They thought shooters would want to use it with really light bullets for varmint shooting. They were dead wrong. Buyers really wanted to use it for deer and when they tried heavier (95grn) deer bullets, the thing shot like crap. Remington had to drop the .244. Later, they brought it back as the 6mm Rem with a faster twist rate. However, by then the damage was done and it was a flop in the marketplace. They goofed again when they gave their .260 rifles a 1/9 twist when the ideal .260 bullet (140grn) really needs a 1/8 twist. Savage goofed with its model 200 in 7mm/08. They gave it a 1/11 (I think) twist which is just too slow for that caliber.
 
Good answers guys. I will add to the comments about there being an ideal twist rate. My 30-06 has a somewhat fast 1-9 twist and while it shoots 150's well, it definitely shows a consistent preference for 180's.

I was also going to use the football analogy, but was too slow.
 
Thanks for the explanation, I just didn't think that the twist rates are high enough to contribute enough centripetal force to rip apart the metal.
 
Geez...centripital force. I hadn't heard that term since engineering school. Well, whatever force you want to refer to, yes the bullet can come apart with too much spin. I've never had it happen to me, but the only really hot loads I have are in the 220 Swift, and the twist is only 1 in 14. But...rethinking what I just said...instead of a couple of coyote misses in the last several months, maybe the bullet just flew to pieces. Yes...That's my story from now on. Yes Sir! And there was that big buck I missed with the 270...

And that football analogy was great. I wish that I had used it.
 
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