In practice, when shooting at long distances, has there been a difference between the calculated vertical corrections and the point of impact of the bullet.
Dependence of overtwisted bullet at subsonic speeds
- Thread starter UA SOF SNIPE
- Start date
Overtwisted? Ya mean a faster twist than normally needed to keep the bullet stable as it goes subsonic?
In that case, Hornady, on their website has fast twist barrels having a meaningful BC improvement over normal twist rates, across the velocity spectrum, tested by them, with their radar.
I haven't seen any other studies done on it.
In that case, Hornady, on their website has fast twist barrels having a meaningful BC improvement over normal twist rates, across the velocity spectrum, tested by them, with their radar.
I haven't seen any other studies done on it.
In practice, everything is a little different from calculators.
For example, there is a 250 grain bullet and a 300 grain bullet. Calculators say that both bullets will fly stably from 1-10 and 1-9.4 barrels. But no, 250 grain on a 1-9.4 barrel does not fly at subsonic speeds.
A faster twist rate would increase the magus effect on vertical dispersion from a lateral wind, so yes.
-Alex
Are there any existing calculations that would provide accurate data.
For example, a 1.7" long bullet will fly predictably with a 10th pitch of rifling.
I mostly shoot 338 caliber.
Barrett MRAD rifle rifling pitch 1-9.4"
When shooting 250 grain bullets, the calculator gives the correct vertical values, but only up to the start of transonic speed.
But 300 gray siera flies predictably up to 1700 meters
Overall stabilty in subsonic region is more difficult to calculate/simulate in subsonic flight, than in supersonic flight. For a mere gyroscopic stability, the aproximation is more complicated than for supersonic region (Where Miller stability criterion can be used). Behavior depends from case to case. Some radar based plots of rifle bullets bahaviour in transonic down to deep subsonic region can be seen in my thread:
https://www.snipershide.com/shooting/threads/subsonically-bad-bullets.7211172/
I have more, but haven't post them
https://www.snipershide.com/shooting/threads/subsonically-bad-bullets.7211172/
I have more, but haven't post them
Still, I am inclined to think that there are no bullets that perform poorly at subsonic speeds.
There is not the correct twist of the barrel for a given bullet and there may not be a suitable muzzle velocity.
But that is a pretty ugly calculation to run on a bullet rather than a cylinder. Would break it up into .050" sections if you really wanted an answer. Since wind velocity is essentially never constant across a bullets flight path at any of the range we are concerned with, it isn't going to be an especially accurate number no matter what. I'd be curious to see how AB handles the calculation. Pretty much has to be an approximation.
-Alex
