OVERSPIN ??? twist and bullet spin

[Bravo 4]

thanks guys...Nemo Arms ...Kalispell MT...military AR platform..1500 yrd military weapon...look em up...Im waiting for a return phone call

Though their .300 win mag rifles have a 1-8" twist listed on their website I believe it to be a misprint. Guess you'll find out if they call you back. Here is a video of a rep and one their rifles saying its a 1-10" twist:
[ame]http://m.youtube.com/watch?v=asBjqOx1txY[/ame]

 

[AKGuide]

Only time faster than a 10 twist is needed for a 30 cal is with the 240 smk if you cannot push it faster than 2900 fps you need a 9-9.5 twist. Also the cutting edge bullets in the 200 grain variety need at least a 9.5 twist to stabilize properly. My next barrel will be a 3 groove 9 twist. Just so I may shoot the heavy monometals like the cutting edge and also the 200 LRX without losing stability at long range.

Reuben

 

[Gerard Schultz]

My take on twist is:

1. Jacketed bullets are more affected by overspin than monometal bullets. As mentioned, spin a jacketed bullet fast enough and centripetal force will pull it to pieces. Also, as mentioned, any anomaly in jacket thickness or inclusions (dirt, air) in the core will be enhanced by a tighter twist. Monometal bullets do not have these problems as long as bullet weight is constant within less than 0.5%.

2. Stability across the trajectory falls into three major categories: Gyroscopic stability (Sg), dynamic stability (Sd) and tractability. The requirement of punching paper and steel, differ from the requirement of terminal performance in tissue.

3. Stable flight will generally happen when the gyroscopic stability (Sg) of a bullet is above 1.1/1.2. It is accepted that stable flight is a given with the Sg above one but that is sailing very close to the wind. So, for target and tactical shooting, stable flight is ok. For hunting, where there is the additional requirement of terminal performance, just having stable flight is not ok. The Sg at launch must be higher and one bullet cannot do all.

4. If a bullet has gyroscopic stability at launch, it will have gyroscopic stability across the entire trajectory. A bullet may destabilize because it starts yawing as a result of becoming dynamically unstable due too high a launch speed. That is a design parameter and it is important to pick a bullet that is intended to be launched at more than what your rifle is capable of, to be safe.

5. Tractability only becomes a factor with typical .284"/.300" caliber when distance is over 500/600.

6. Overspin (high Sg) is especially useful for short distance shooting with monometal bullets such as for bush and dangerous game.

7. The original question: An 8" twist in a .300" caliber would be very good for hunting to 600/700 with long bullets in mono around 180gr and in jacketed lead 210 and up. For further than 700, longer monos must be looked at.

 

[MagnumManiac]

Contrary to what most people take as gospel, the myth of over stabilized is just that, unless a ridiculous amount of twist is used. The most accurate twist is the one that just stabilizes the bullet at the desired velocity. A 1:13" twist in a 30cal above 3300fps for a 155gr bullet is ideal, it will not sufficiently spin a 180gr or heavier bullet to be stable unless it is a short RN design and the velocity is high.
A bullet that is spun too fast is still stable, as in bullet tip polnting to target and not wobbling around it's axis, but a high spin rate can cause the core to slip in the jacket resulting in total bullet break up. It also can cause poor groups due to any imperfections causing a slight yawing while it travels to the target. Another possibility is the bullet failing due to the jacket stripping the rifling, the starting and stopping of the spin causes the jacket to fail before the bullet leaves the barrel.
I witnessed this with Speer 125gr THT HP's fired from my 28" barreled 300WinMag, velocity would have been in excess of 3600fps, a fellow shooter informed me that a 'blue streak' was appearing about 25yrds from the muzzle and no holes were in the target, apart from some peppering from the shrapnel of the bullet jacket. I asked him to shoot the rifle so I could see the results for myself, yes, there was a blue streak downrange about 25yrds from the muzzle and molten lead was also seen on the targets at 50yrds.
A 1:8" twist is very fast in 30 cal, the srandard 1:10" twist serves very well for almost all bullet weights, including the 240gr SMK as long as the velocity is high enough.

Cheers.
gun)

 

[ZSteinle]

I would like to see bullet manufactures list the maximum RPM rate for their bullets. This would really help choosing a twist rate for those ultra high velocity chamberings. For instance my 22-243 with a 7 twist will shoot the 90gr. VLD's all day long. load up an 80 grain amax and poof. It will explode before it makes it 100 yards. Thinking of building a 7mm-300 norma mag with a 8.5 twist for the new 195 bergers whenever they do come out but worried with an 8.5 twist will the 168's or 162 amax blow apart? Maybe berger will lead the way and list this information.

 

[elkaholic]

I would like to see bullet manufactures list the maximum RPM rate for their bullets. This would really help choosing a twist rate for those ultra high velocity chamberings. For instance my 22-243 with a 7 twist will shoot the 90gr. VLD's all day long. load up an 80 grain amax and poof. It will explode before it makes it 100 yards. Thinking of building a 7mm-300 norma mag with a 8.5 twist for the new 195 bergers whenever they do come out but worried with an 8.5 twist will the 168's or 162 amax blow apart? Maybe berger will lead the way and list this information.

What you say is very valid. I've learned this from making bullets and it would be a great additition from the manufacturer.....Rich

 

[Canadian Bushman]

Deleted

 

[Kennibear]

I have a factory Colt Sporter AR w/ 1 - 7 twist that shreds Sierra 69gr SMK's. The description "blue streak" is accurate. They would come apart at 75 yds with the appearance of a grey/blue fog in the sights. Not a good sight during a DCM match.

1 - 10 is such a proven formula in 308 why mess with it? In 300WWinMag? What kind of bullet requires that? For any bullet that can be driven at 2700 fps or more 1 - 10 twist is plenty.

My $0.02 is not to risk it.

KB

 

[Michael Courtney]

I would like to see bullet manufactures list the maximum RPM rate for their bullets. This would really help choosing a twist rate for those ultra high velocity chamberings. For instance my 22-243 with a 7 twist will shoot the 90gr. VLD's all day long. load up an 80 grain amax and poof. It will explode before it makes it 100 yards. Thinking of building a 7mm-300 norma mag with a 8.5 twist for the new 195 bergers whenever they do come out but worried with an 8.5 twist will the 168's or 162 amax blow apart? Maybe berger will lead the way and list this information.

The maximum spin rate (RPMs) does not only depend on the bullet, but also on how much the trip through the rifling weakens the jacket (scoring).

Consequently, it is as much dependent on the rifle it is fired from as on the characteristics of the bullet. One rifle with sharp rifling might have a much lower RPM to cause the blue streak than another rifle that does not score the bullets as much.

 

[Gerard Schultz]

denobravo,

The bottom line is that you would not generate enough stress on the jacket of a bullet fired from a 300WM to do harm unless one gets silly and uses a very light and short match type bullet with a thin jacket.

An 8" twist will hurt nothing at shorter distances and allow the use of long bullets that are better for getting to longer distances.

What make of rifle is this that you are considering?

 

[denobravo]

denobravo,

The bottom line is that you would not generate enough stress on the jacket of a bullet fired from a 300WM to do harm unless one gets silly and uses a very light and short match type bullet with a thin jacket.

An 8" twist will hurt nothing at shorter distances and allow the use of long bullets that are better for getting to longer distances.

What make of rifle is this that you are considering?

I am looking at an AR 300wm from Nemo Arms...talked to them yesterday...they have the 1-8 twist for the sierra 240's ...sniper bullet...1-9 minimum....love your bullet line...tooooo spendy for me though..sweet stuff!!
Thanks for your input brother
deno
ps...thought I had posted a reply about all this ...didn't see it though

 

[denobravo]

CANNOT find the reply I THOUGHT I had posted about this subject...
Bryan Litz from Hornady...said no problem except for light or thin jacketed bullets
Nemo Arms said they TRIED to vaporize bullets and couldn't do it...subject is closed in my mind for now....I really appreciate ALLL the comments....my conclusipon concerning current technology...a bullet cannot be over stabilized......might go to fast LOL...but cannot over stabilize...thanks