[willyp]

You ever wonder who decides what twist rate a rifle should have and why ?

 

[Takemrarely]

Nope.

 

[USAF_SP]

There is a mathematical formula used to determine optimal rate of twist for a given bullet. I forget what it is, but is uses diameter, velocity, and length of bullet.

 

[willyp]

Greenhill Formula.

 

[triggercreep]

Faster is better with quality bullets. Bullets weren't as concentric years ago when we saw a lot of 1:14" twists in varmint rifles. Those slow twists better stabilized bullets that weren't perfectly balanced but the didn't really stabilize heavy bullets. Your light bullets will still shoot well out of let's say a 1-9" twist as long as the bullets are quality, and it's what is needed for the heavy bullets. Slow twist killed the .244 right out of the gate but fast twist made the .243.

 

[yobuck 1]

Slow twist killed the .244 right out of the gate but fast twist made the .243.

Not sure if that should be blamed on the twist or the brain trust at Remington not knowing how to deal with another winner.
I guess it goes back to the original question.

 

[Gunnermhr]

Twist rate is an optimal number based on the length of the given bullet and projected velocity. If the twist rate is too fast, the bullet will literarily blow up. Usually within a 100 yards. If the twist rate is too slow the bullet will begin to tumble though the air, although this is more uncommon and is generally only seen at extreme distance. You can see it on paper where the bullet doesn't cut the paper in a nice circle, it will create an oblong hole. Most bullet Manufactures publish the optimal twist rate for their bullets.

The published data isn't the gospel, for instance Berger recommends a 10 twist for their 210VLD, I know a lot of guys using an 11 Twist for that particular bullet.

A Remington 243 comes with a 9.125" Twist. That is a real general twist for a variety of bullets, it covers everything from the 107 grain bullets to the 70 grain bullets. But optimal for a 107 grain Target bullet (Longer than Hunting Bullets) would be an 8 twist. Which too is subjective. Some guys like 7.75" twist for longer bullets. Some guys will use a gain twist barrel, starting at the breech with 8.8" and getting faster towards the muzzle 7.5". Sierra actually recommends a 7twist for their 107SMK. Which by the way no one I shoot with uses a twist that fast.

Bullets tumbling or exploding will not be witnessed by the general hunting crowd. But under match conditions where guys are trying to push the accuracy envelope you occasionally see it happen. Most of the time when a guy is experimenting with different bullets vs twist rates. Say a 210VLD in a 14 twist, pushing high velocity, for sure you'll see a little black cloud of lead about 80 yards out. You probably wouldn't see it happen with the same situation under a reduced load. As you might see it tumble with the same bullet in an 8 twist barrel shooting 2000fps

 

[6-DASHER]

Gunner, do you remember my Buddy Ken exploding those Bib's out of his .243 AI, it's pretty cool to see and you can see it, it looks like a flash of oil on water for a milli-second, really bright colors, about the size of a basketball.. I'm assuming are lead/copper going from solid/gas/plasma states..something everyone should whitness at least once..not sure you could even video it with a digital camera, you'd have to have a high speed one to see it..

 

[Strut10]

Load some Speer 110 grain round nose in a .300 Win or Wby if you wanna see it. Not even a fragment makes it to the 100 yard backstop.......

 

[Gunnermhr]

I remember dasher, it's really cool to see! Your right strut, nothing ever touches the target.

I've seen bullets exploding way more times than tumbling, I might have seen them tumble only 1 or 2 times