Gyrospic Stability and Precision

[gitano]

If you have a look at the link posted in post number 18 in this thread http://thehunterslife.com/forums/showthread.php?t=15072&highlight=Gyroscopic&page=2, you'll get a idea about the effect of imbalance in a bullet due to inconsistency in density of a bullet. The pathway the bullet describes is a helix/spiral. If you were to look straight down the path of travel, you couldn't see the 'spiral', all you could see would be a 'circle'.

I bought a model 700 Remington chambered in .17 Remington in the early '80s. I had to buy a box of factory ammo in order to get brass to reload. I shot that box of factory ammo up, and was soon reloading. It didn't take long to get to a load I was 'satisfied' with - 1 MoA. I'm a Hunter, not a target shooter, and when I achieve that level of precision, I stop 'hunting' for more. Such was the case here. However, there was something "odd" about the groups.

That model rifle holds 10 rounds in the magazine, and I often shot 10 rounds at a target. EVERY TIME I did, I got the same thing: almost a perfect CIRCLE of bullet holes one inch in diameter! EVERY time! I found this 'curious', but I didn't care much about it because it satisfied my personal precision standard of 1 MoA. "Interesting" but not worth wasting time or money on 'figuring out'.

For years I read about how bad the "early" .17 Remingtons were because the twist rate of the rifling was too 'slow' - 1:10 - to 'stabilize' the 25-grain bullets. I didn't pay much attention to that because I was "fine" with what my rifle did - 1" circles at 100 yd - with 25-grain Hornday bullets. But that CIRCLE was always in the back of my mind.

Fast forward 20+ years and a bit more experience, and all of a sudden the 1" circle was no longer a mystery. I have one of the "old" 1:10-twist rifles. That twist rate doesn't PERFECTLY stabilize that 25-grain bullet. As a result, the bullet is inscribing a spiral as it wends its way down range. Where on that radius of the spiral (the circle) the bullet hits the target is random, thereby cutting what is essentially a 'perfect' circle of bullet holes 1" in diameter at 100 yd. Perfect physical proof of the effect of incomplete gyroscopic stability.

Furthermore, I suspect that this sort of phenomenon MAY explain "going to sleep" of some bullets. In other words, shooting smaller groups at longer ranges than they do at shorter ranges. That spiral is actually having to "work" to maintain itself. In other words, physics is forcing the bullet to a smaller and smaller spiral the longer it spins. I think that if those that observe bullets "going to sleep" were to shoot 10-shot strings, they might see the same 'circle' I observed with my .17 Rem.

Paul