twist rate effects bullet performance on target?

[JDJones]

I'm thinking about putting together a 6mmBR for varmints , the plan is to shoot light bullets (55-70gr) fast for max explosion.

My question is would a 55gr bullet shot at 3500fps have better on target "POP" if it was shot out of a 1-8 twist as opposed to a 1-14 twist.

In my mind it seems that the raised RPM's from the 1-8 twist would cause the bullet to explode outward more violently at impact than at a lower RPM when shot from a 1-14 twsit.

any of you folks have any experiance with this at all , this will be my first rodeo with the 6mmBR , up till now I've only ever used barrel burning hot rods like 22-250 Ai and 243 Ai

 

[cmillard]

you might have trouble getting the bullets to stay together. the strain being placed on that bullet jacket is pretty big. not saying that it can not be done, but you might smoke some bullets

 

[Phil]

I`ve always used the 14/12 twist in my 6br/dashers.....

I prefer the straight line velocity over anything i will gain,in explosiveness,with rotational velocity......

The 55 Nosler is a tuff SOB.....that being said i`m gonna try the 58gr V-max and see if there is a diffrence.........

 

[JDJones]

Phil , what kind of velocity do you get with thr 55gr bullets and what sort of range??

 

[spclark]

1:8 for a 6BR is typical for bullets from 100 grains & up. The lighter the bullet (generally) the shorter too where a slower twist works best.

Spin the lightweights (actually ANY bullet) too fast & they often "disappear in a grey cloud" on the way down range! I think anything faster than 1:12 for most 55's would be asking for trouble.

 

[Phil]

JD,

I`m pushing 4000fps with the 6br and Nosler 55`s using AA2230 and a 28" barrel.

I`m hoping to duplicate these results with the Dasher and 58gr V-maxes, but i haven`t had the time to get any results yet......

Phil.

 

[camac]

You will probably also lose a little forward velocity going to faster twist rate. This may lose a bit of the "pop" factor anyway at 3800+ for 55's in 6mmBR you don't need to go searching for any more pop.

I started with a 12 twist but soon realised it was so accurate that it left me wanting more in the range department. The best reason to go to 8 twist is give you the option of going up the bullet weight class and take on those varmints at crazy ranges. That is where the real difference will come between what you are used to and the 6mmBR. Get a wind and elevation chart and 1000 yard prairie dogs are possible (rabbits for us) you can still load the lighter bullets anyway for all that short range stuff.

 

[moorepower]

A .243 will shoot the 55's at 4K with a 1-10 and no issues. I will let you do the math on rpm.

 

[BBTC48]

62gr Barnes Varmint Grenade. 6mm. Red mist Special. Call 'em for a free DVD and bullet brochure. They explode when hitting grapes and cherry tomatos !! Yup, you'll dig the hunting video. these are filled with a lighter than lead material and are a bit longer than normal due to this. (tree huggers are gonna kill lead filled ones)

 

[zcrackshot]

I actually wondered about this myself. I have a 6.5 swede that strikes animals like lightning when kept inside it's potential range. It has a very fast 1 in 7.78" twist rate and I thought that maybe that had something to do with what the bullet does on impact. Maybe it's just me but it seems like the wound channel left by the bullets shot from this rifle seem abnormaly large, especially since I don't push it for velocity even though it's a modern action not a mauser?

 

[Klong]

I do not think it matters for high velocity projectiles. If you do the math, a projectile in a 12 twist barrel leaving the barrel at 3000 fpm will exit at 180,000 rpm. Same projectile and velocity in an 8 twist is 270,000 rpm. I know there is a difference of 90,000 rpm, but I think they are both such a high rpm it does not matter. Kind of like discussing crashing into the ground at 1000 mph or 2000 mph, either one is total destruction.

You may convince me different if you have evidence of the exact same type bullet impacting at the same velocity out of 2 different twist barrels into the same animal at the same distance into the same spot on the same size animal of the same type and producing two completely different wound results.

 

[spclark]

"I know there is a difference of 90,000 rpm, but I think they are both such a high rpm it does not matter."

True enough but consider that as rotational velocity increases the forces acting on a rotating body go up geometrically, not linearly. That extra 90,000 rpm creates maybe four times the force trying to pull the jacket off your bullets as at the lower speed.

That's the main reason Berger went to their thick jacket design for target bullets. The thinner jackets they'd been using weren't holding up well under the stresses encountered in competitive shooting.