Home Forums Hunting & Shooting Ask The Gunwriters Bullets Corkscrewing Along Trajectory

No, it explains why what you claim isn't possible.
Bryan Litz wants to see you shoot to prove it's true.
He will pay your expenses if you can show him.

Does this phenomena have anything to do with what Litz wrote about Nosler's LRAB BC (and his BC bullets in general) being overstated if the bbl is "under-twisted" or the bullet is slightly under-stabilized?

The way I look at it a bullet in flight that is not optimally stabilized due to twist rate is exposing a larger frontal area to the atmosphere, thus reducing its effective BC.

A few days ago, I had cause to do some digging on this topic. It seems like something worthwhile reporting here. Enjoy:

My main source is Harold Vaughn's Rifle Accuracy Facts. Harold was in charge of handling the fluid dynamics computations for our country's ICBMs, and he held a doctorate in the field. He was also a hard-core experimentalist, dragging a big old Tektronix 555 oscilloscope (I had one of those once.) and gas generator into the field to make measurements. If you want to understand how his work is regarded, try buying a used copy somewhere.

Question 1: Does the nose of the bullet trace out a spiral as the bullet flies? Yes. Harold developed software that accurately models the situation. The software is capable of six degrees of freedom, i.e., it handles position in three dimensions and angles in three dimensions. Here is one of the graphs he produced.



Question 2. Does this cause the bullet to corkscrew around its trajectory? Yes. It must be so, because the bullet is "coning" and the drag vector always points from tip to center of base. When the bullet nose does not point exactly along the trajectory, the drag vector has a transverse component that moves the bullet sideways and up and down. Fluid dynamics substantially changes the situation, vs. ballistics in a vacuum.

From page 182:


Question 3. Is this effect important to most of us? No. From page 192:


Bryan Litz's money (he issued a challenge for anyone to show a rifle more accurate at 200 yards than at 100) is probably safe unless someone with a lot of patience and a superbly accurate rail gun chooses to compete for it.

Keyholing at 100yd, accurate at 200 and 300yd....? More accurate at 600 than 300?

Litz would love to talk to you...but of course, the upper isnt around anymore..

I think it's important to clarify whether we're talking about absolute accuracy, as in group size in inches, or relative accuracy, meaning measuring groups in angular terms like MOA. A 0.5" group at 100 yards is ~ 0.5 MOA. A 0.75" group at 200 yards, while larger than the 100 yard group, is only ~0.375 MOA. So it's relatively more accurate (MOA), but less accurate in regards to absolute group size (in inches).

I'd love to see a quantification of the relationship of the maximum deflection and GS.

Accuracy is a matter of placement relative to POA.

Precision is the term used in reference degree of dispersion. Dispersion is just that, whether it be measured inches/mm/angstroms or MOA.

Manufacturers don't make a precision guarantee

I'm aware of that, and have been a bit bothered by the industry standard terminology myself, at times, but that's simply the way it's spoken of across gun culture. Manufacturers don't make a precision guarantee, they make an accuracy guarantee (guarantee that your scope will be accurately zero'd?? ). I was more referring to the fact that Bryan Litz and others are talking about a rifle shooting better at longer distances than shorter ones. Are they talking about absolute accuracy or relative accuracy? I've never seen a rifle that shot smaller linear groups at distance, but I have seen and owned rifles that shot smaller angular groups as the distance increased.