bullet twist rates over velocity?

Nighthawk

Well-Known Member
Hey guys, I figure I would ask a question to stir the pot. I know that a lot of people on this site like to go for the highest velocity they can get without sacrifising accuracy in order the get the maximum range out of their rifle before the bullet decides to destabalize. My question is this. Wouldn't it be better to run a higher twist rate at a slightly slower velocity with possible improved accuracy over a higher velocity. Wouldn't the higher twist rate make up for the slight loss in velocity?

G

Guest

Guest
Lower velocity = longer time of flight = more time for wind to effect! With the same projectile and BC obviously.
The holy grail is best accuracy at highest possible velocity with the best practical BC. This gives shortest time of flight with best wind bucking projectiles.

Richard338

Well-Known Member
Higher than necessary spin increases the effect of dynamic imbalance. Of less concern, it increases spin drift, and the vertical component of horizontal crosswind deflection.

Nighthawk

Well-Known Member
What is dynamic imbalance?

Richard338

Well-Known Member
If there is an imperfection in the bullet, then there can be two types of imbalance, static, and dynamic.
Imagine a perfect bullet, then imagine adding a small lump of mass near the front, on the left side. Add another at the back, also on the left side. This is statically imbalanced, you can detect it while the bullet is motionless. If you rotate the bullet on its axis, it will be heavier on the side where the extra masses are. The axis that the bore forces the bullet to rotate around does not pass through the center of mass. Once free of the bore the bullet flies off it's path slightly.

Dynamic imbalance occurs if the mass at the back were on the right side, then it would counter the mass at the front during static measurements. Once the bullet is spinning fast, the mass at the front would pull opposite to that at the back. This twists the bullet from flying straight along its trajectory.

Both effects are bad for accuracy. The different densities of copper and lead, and any deformation of the core and jacket cause these imbalances.

308sako

Well-Known Member
Try though I may, I am unable to believe that a higher rate of spin would not increase expansion. Many posters on AR site tell me that it's frontal velocity that does it all. I was interested in putting together an overly twisted .308 to try to expand some bullets, but feel that the project isn't worth the effort after the replies I recieved. Some would say that you cannot overstablize a bullet, while others think that the imperfections will cost you the ranch. The only way appears to buy the package and try it out. Good luck either way.

Michael Eichele

Well-Known Member
The higher the rpm's the more explosive it will be. Its called centrifical force and is proven.

Most bullets will loose stability when they reach sub sonic speeds whether it is slightly over spun or not. If you spin the bullet faster but lower the velocity you will go transonic sooner and shorten the range.

Spinning a bullet a healthy amount more that it needs to be can and in most cases decay the BC faster than normal. Less BC = more TOF. More TOF = more wind drift and more bullet drop. I am NOT saying use a twist slower than what is needed but using one much faster than needed when using most popular components will not help the overall performance. If the highest performance is the goal shoot bullets that your twist was desighned for or build a rifle with a twist desighned for the bullet (s) you wish to use and use that rifle with in the parameters is was made for.

This is of course for best results only.

[ 10-22-2004: Message edited by: meichele ]

Nighthawk

Well-Known Member
Richard, does this static and dynamic impalance apply for solid bullets as long as they are relatively "perfect."

Richard338

Well-Known Member
Harold Vaughn (Rifle accuracy facts)calibrates his device to measure imbalance with solid bullets. He drills tiny holes to produce known amounts of imbalance to set up his device. As you point out, having the bullet made from one material leaves only structural defects. (I'm not saying that solid bullets are better, I use jacketed myself)

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