I can say this, from experience with muzzle loaders, round balls like slow twist rates. (1 in 66 or 72)Conicals like faster twist barrels.A all around twist 1 in 48, it does both adequately, but not exceptionally.And 1 in 28 is intended for long cast bullets I have experienced this in 32 caliber, and .45 caliber and .50 caliber shooting.Now I know an air rifle is not a muzzle loader, but they both shoot soft lead, and both power plants act similar.Also, what velocity are you getting?And if you have a very soft heavy bullet, with a very fast twist, it may not stabilize correctly as the mass is just too much to start spinning that quickly.Some barrels have a gain twist, that start slowly, then increase the spin rate farther down the barrel.Not air gun related experience, but an insight from another hobby shooting big heavy projectiles.
Twist at the basic level is measured in calibers, and relates to the bullet length, also in calibers.... A bullet that is 2 calibers long requires a given twist in calibers.... so that means as the caliber increases, the twist in inches does as well.... Therefore a .44 cal bullet 0.88" long needs HALF the twist rate (1 turn in twice the length in inches) as a .22 cal bullet that is 0.44" long.... Yes, longer bullets require a faster twist, but larger calibers require a slower twist.... If you give me the bullet length and the nose and base diameter I can give you a rough idea of the optimum twist for your bullet.... assuming subsonic flight....Bullets that are spun too fast tend to start to wobble because the high RPM emphasizes any imperfections.... In addition, when shooting at long range, then tend to impact the target nose high.... The optimum spin rate is one that produces a stability factor of roughly 1.5, with under 1.0 being unstable.... The Military tend towards an SF = 2.0, while bench-rest shooters opt for about 1.2.... SF's of over 4.0 tend to cause groups to open significantly.... even a lower SF can be a problem with less than perfect bullets....The worst velocity for most bullet shapes is a few fps below Mach 1, that is where they are the least stable....Bob
has it been determined what's the cause of spiraling pellets and pellets turning off the direct flight path? I get decent groups at 50M but when I go to 100M those pellets start hitting right of the target and you can actually see them turning off the flight path, too much spin?
My guess would be too much spin, but I can't prove it....