Bullet RPM and performance

This is fascinating stuff to me! I'm just an old-school reloader. I pick a caliber, I pick a high quality bullet of the appropriate design for the job at hand, I pick a powder that my reload manual likes and that will produce the desired velocity and I start cranking out ammunition. If new components are in use, I go to the range and fire a dozen of my reloads, just to make sure they are doing what I want and I'm a happy camper.
If I get into a new caliber, I trust that the science has been done and I trust the manufacturers and the current reloading manuals to keep me inside the rails.
Having said that, in a moment of youthful exuberance about 50 years ago I found and bought a .350 Remington Magnum in a Model 600. I was anticipating a move to Alaska and thought it would make good Brown Bear medicine. As it happened, it made pretty good me medicine and I have the scope scar to this day to prove it. With more experience and a little more growing up and more muscle mass it was shootable and I have continued to reload for it and shoot it ever since. But I sure was happy when I finally found a Model 700 in .350 Rem mag that I could shoot with a scope without worrying too much about adding to the ruggedly handsome man I have grown into by adding another scope scar!
 
Most of my twist rate observations have been with the 6.5 caliber cartridges using lead core bullets which I have shot most frequently over the past 20 years or so for both competition and hunting with 8.5, 8, and 7.5 test barrels. I don't buy into recent craze to automatically go with fastest twist barrels. You can't over-stabilize a bullet. Alternatively, I don't use bullets that are prone to blow-up due to over-spinning them at very high velocity. My practice is to use the slowest twist that will fully stabilize my bullets(min 150-175SG). I don't simply pick the fastest twist. From my experiences, I seem to get better and more consistent accuracy with less fouling effects at high shot counts with intermediate 8tw barrels using the 140 class, and more recently, even the 156gr bullets(that exhibit a relatively long bearing surface) which stabilize well at my velocity/conditions and perform well on game at distance. I also believe that the faster twist may be harder on the throats.
 
dblman said:
What caliber, what weight, what fps, what twist? All must fit.
Mine is 6.5 @ 2753 fps, 1:7 twist, 143 gr, devastating 100 to 600 on hogs, deer and coyotes all actual kills.
Click to expand...
Go to that thread I told the whole story it was a 22 creedmoor 7 twist barrel this happened while we were still learning about twist rates versus velocity he's had trouble out of 3 barrels with 7 twist mine is a 7.5 twist knock on wood I haven't had that problem. David
 
david g ranes said:
Go to that thread I told the whole story it was a 22 creedmoor 7 twist barrel this happened while we were still learning about twist rates versus velocity he's had trouble out of 3 barrels with 7 twist mine is a 7.5 twist knock on wood I haven't had that problem. David
Click to expand...
I told joejack now I know why I miss all those running coyotes my bullets are blowing up that's my story and I'm sticking to it. David
 
Darryle said:
Hopefully I am not beating a dead horse here or asking an ignorant question.

I have read about twist in relation to bullet stability and velocity in relation to bullet performance at long range. I just can't recall about reading if RPM contributes to bullet performance (i.e mushrooming and transfer of energy).

I know we have all read instances of penciling, the ELD-X bullets are one I experienced first hand and at a variety of ranges.

My questions are:

Have designers taken barrel twist/bullet RPM into consideration when designing these bullets and as twist rates get faster, ranges increase, bullets get longer and velocities get higher are these contributing factors to bullet design and performance?

Can you spin a bullet too fast to inhibit performance, increase failure or increase the chances of getting penciling?

Does spin have an affect on performance and has a single design been subject to testing at differing velocities, RPMs and ranges for terminal performance or has the data been gathered?

Is there a way to know you are in the sweet spot in relation to twist and bullet/load selection other than accuracy at the range?

I am in the process of deciding on a new barrel and other than stability for the chosen bullets, I am wondering what other effects twist will play with my selection.

Thanks Darryle
Click to expand...
To spin a heavy object from 0 to 240,000 rpm in 3 milliseconds means the barrel rifling is experiencing tremendous forces and very significant energy is transferred into rotational kinetic energy vs forward motion kinetic energy. However, I'm not an expert except to say the last time I analyzed this I couldn't figure out why, on paper, a bullet needs to be spun that fast. Rifling was invented in the mid 19th century by studying empirical results, not on paper. So I think to a certain extent its not exactly understood why it works but only that it does work. Men of European heritage are good at inventing mechanical things intuitively without understanding the theory behind it, the steam engine for instance. To my mind rifling and spin falls in that category but I could be wrong. I know the French invented the modern bullet design just before the civil war so I assume they invented rifling, but either way rifling was invented around that time. The French invented/discovered a lot of things between 1750 and 1850 and then stopped for some reason.
 
Mike from Texas said:
The biggest issue comes in finding a twist that will work for both cup/core bullets AND monos. You have to sacrifice somewhere and there will be trade offs.

If you pick a fast twist, you potentially box yourself into only shooting mono bullets. If you pick a slower twist then you have to shoot a lighter weight mono typically and sacrifice bc. Whether or not penetration is compromised is another topic.
Click to expand...
My .257 WBY has a 1:7" primarily built to propel the 131 BJs and 133/135 Bergers and the 110 BD2s and 117 Cayugas.
 
Retired CPO said:
This is fascinating stuff to me! I'm just an old-school reloader. I pick a caliber, I pick a high quality bullet of the appropriate design for the job at hand, I pick a powder that my reload manual likes and that will produce the desired velocity and I start cranking out ammunition. If new components are in use, I go to the range and fire a dozen of my reloads, just to make sure they are doing what I want and I'm a happy camper.
If I get into a new caliber, I trust that the science has been done and I trust the manufacturers and the current reloading manuals to keep me inside the rails.
Having said that, in a moment of youthful exuberance about 50 years ago I found and bought a .350 Remington Magnum in a Model 600. I was anticipating a move to Alaska and thought it would make good Brown Bear medicine. As it happened, it made pretty good me medicine and I have the scope scar to this day to prove it. With more experience and a little more growing up and more muscle mass it was shootable and I have continued to reload for it and shoot it ever since. But I sure was happy when I finally found a Model 700 in .350 Rem mag that I could shoot with a scope without worrying too much about adding to the ruggedly handsome man I have grown into by adding another scope scar!
Click to expand...
Well said!
 
Greyfox said:
Most of my twist rate observations have been with the 6.5 caliber cartridges using lead core bullets which I have shot most frequently over the past 20 years or so for both competition and hunting with 8.5, 8, and 7.5 test barrels. I don't buy into recent craze to automatically go with fastest twist barrels. You can't over-stabilize a bullet. Alternatively, I don't use bullets that are prone to blow-up due to over-spinning them at very high velocity. My practice is to use the slowest twist that will fully stabilize my bullets(min 150-175SG). I don't simply pick the fastest twist. From my experiences, I seem to get better and more consistent accuracy with less fouling effects at high shot counts with intermediate 8tw barrels using the 140 class, and more recently, even the 156gr bullets(that exhibit a relatively long bearing surface) which stabilize well at my velocity/conditions and perform well on game at distance. I also believe that the faster twist may be harder on the throats.
Click to expand...
What you said, plus I tend to think the rifling/barrel may last longer. (Enough to do the job is enough)
 
I found at least one of the sources: a post on accurateshooter.com's facebook page known as Tuesday Trivia dated July 23, 2013. Bryan Litz presented this subject as a true or false question. He mentions three potential problems with bullets in flight: Yaw, Precession and Nutation. Lots of shooters opined or left comments as to the validity of over-rotation effects on a bullet. Near the bottom of the page, Bryan gives the answer (look for post dated July 25, 2013). The basic statement is false: over-rotating a bullet does not seem to effect yaw, precession or nutation. However, it is possible for this phenomenom to occur in a situation where the incline of the barrel goes above 10-20 degrees - which could occur in long range shooting situations.
 
I think the football analogy doesn't work. I think the football will stay point up not because of too much spin but because it started out point up too much. In other words, the football started out with the point higher than the plane it is traveling on.
 

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