Barrel rate of twist

[FearNoWind]

With no intention of taking sides in the argument, I'd like to thank you for raising the issue of what happens when a thread gets cold or when a nub joins a forum. Regardless of the topic, I believe it's important to qualify various technical information (and sometimes personal opinions) so that those who may not be as experienced with shooting and reloading don't become mislead by what is posted on any forum.

 

[Gerard Schultz]

Michael, I hear you and the danger is that most readers will think that they can use the Miller Formula for any type of bullet as a result of this and other threads. Is it not time that we get away from perpetuating the myth that twist is somehow tied to weight? The fact is that twist rate is tied to bullet length, firstly, and bullet shape secondly, more so than what it has a relationship to weight.

All that has to come across is the realisation of:

That fact that miller doesn't work perfectly with monos...

That makes it relevant to any thread where twist calculation is mentioned. I realise that you favour jacketed lead and that I favour monos but that does not mean we have to continue leading people down a road that is not right.

 

[Michael Eichele]

I get what you're saying. You have to remember that what we are arguing about here does little to help the original poster as to whether or not his new 12x barrel will work with 185 and 190 grain VLDs.

The answer to that question is simple. Yes, it will work. Miller, greenhill, Lilja, real world results or any other method or calculation will agree that the original posters barrel will work with what he wants except for the 215s. You do realize that the miller formula also includes length right? Not just weight. The issue with it is that it doesn't use specific gravity. Hence the reason it maybe considered invalid for monos. Miller still has a strong place for calculating twist with jacketed lead bullets.


You have great points and are sharing great info. I can't disagree with your assessment here. The facts are the facts. That said, we have hijacked this thread. Have you considered writing an article about the subject? At the very least, a thread. I'm betting Len would even make it a sticky if you asked him to.

I appreciate your insight, knowledge and contributions to this site but we both along with others need to talk twist and it's relationship to bullets design, specific gravity, atmospheric conditions etc...in another thread and not continue to hijack this one. Agreed?

I look forward to a dedicated thread on the subject.

M

 

[davkrat]

Michael, I hear you and the danger is that most readers will think that they can use the Miller Formula for any type of bullet as a result of this and other threads. Is it not time that we get away from perpetuating the myth that twist is somehow tied to weight? The fact is that twist rate is tied to bullet length, firstly, and bullet shape secondly, more so than what it has a relationship to weight.

All that has to come across is the realisation of:

That makes it relevant to any thread where twist calculation is mentioned. I realise that you favour jacketed lead and that I favour monos but that does not mean we have to continue leading people down a road that is not right.

If you follow the link to the Berger twist calculator that was posted first it calculates based off caliber, weight and length which should account for any change in density.

http://www.bergerbullets.com/litz/TwistRuleAltWP.php

 

[Gerard Schultz]

If you follow the link to the McCoy calculator, you will see that also asks for the ogive length and meplat diameter, boat tail length and end diameter and so on.

It calculates center of gravity and a host of specific parameters that the Miller Formula assumes as a general constant.

For example, how would the Miller Formula know the difference between two bullets of equal length and weight but one has a secant ogive and the other has a tangent ogive?

NPS Home

You could also use this one, it is also based on the McCoy method.

JBM - Calculations - Drag/Twist

 

[amce]

If you follow the link to the McCoy calculator, you will see that also asks for the ogive length and meplat diameter, boat tail length and end diameter and so on.

It calculates center of gravity and a host of specific parameters that the Miller Formula assumes as a general constant.

For example, how would the Miller Formula know the difference between two bullets of equal length and weight but one has a secant ogive and the other has a tangent ogive?

NPS Home

You could also use this one, it is also based on the McCoy method.

JBM - Calculations - Drag/Twist

The McCoy calculator also requires some input that I, for one, have not seen in manufacturers catalogues or web sites:
- head shape parameter
- ogive length
- density (is this grams per cubic centimetre or grains per cubic centimetre? One must be wary of abbreviations)

Most bullet makers don't even provide length info.

Cheers

 

[Gerard Schultz]

That is why I said to Michael:

Is it not time that we get away from perpetuating the myth that twist is somehow tied to weight? The fact is that twist rate is tied to bullet length, firstly, and bullet shape secondly, more so than what it has a relationship to weight.

So, some manufacturers have to lead again and we have already done so. The average shooter has no interest in such detail but, for those who do, the information should be available. It boils down to what the consumer will accept without contacting the manufacturer to change or present data better. Most manufacturers do not give useable BC data either because every manufacturer has their own ideas and most every manufacturer gives sectional density data for some obscure reason.

The Nano Tech link for a twist calculator has their terminology closer to the McCoy system and hence the head shape parameter. In the JBM calculator, they have made it a bit more user friendly by asking whether it is a secant, tangent or conical ogive/nose and putting in the extra step to do the conversion in the background. Also on the JBM calculator is an explanation of terminology.

http://www.jbmballistics.com/ballistics/calculators/help/drag/drag_exp.shtml

 

[Mikecr]

I haven't read through all this but I agree with you Gerald.
The Miller formula is merely a rule of thumb, and is 'close enough' to truths under limited conditions only.

McCoy's math passes more tests. It's just that its far too difficult for most reloaders to use. So they turn to rules of thumb, charts, or whatever they can work with.
You're not going to be able to change that.