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Old December 30, 2012, 06:02 AM   #9
Bart B.
Senior Member
Join Date: February 15, 2009
Posts: 6,318
Dr. F. Mann proved with slow, heavy lead bullets that corkscrew bullet path happens in the early 1900's. Sierra Bullets also noticed it happening. Note Sierra's bullets were spinning and traveling much faster than the lead ones Dr. Mann used. Sierra also felt that the corkscrew path pretty much settled out in the first 100 yards; they've "gone to sleep" at that range. But the size of it was pretty small else they would not have shot so many groups in the ones at 100 yards in their test range. If you look at the groups fired in 100 to 300 yard benchrest, they're bigger in angle as the range gets longer.

I don't trust data on group angular subtention getting smaller as range increases when group A is fired at a different range than group B. And compensation from barrel whip certainly causes lower velocity bullets to strike the same point of aim at some long distance as higher velocity ones. The Brits proved this over a hundred years ago as documented in the following article "Vibrations of Rifle Barrels (January 1, 1901)"

Click on the "PDF" link in the upper left-hand "View The Book" cell to read this facinating article. No wonder those .303 SMLE"s shot so darned accurate past 500 yards all the way to 1000 with arsenal ammo compared to Mauser 98 style rifles. But this just corrected vertical shot stringing. It's also been observed testing M14NM's in accuracy cradles and their 600 yard groups were a bit smaller angle wise than those at 300 yards with the same ammo and rifle. Gas escaping from the port mid point in the barrel bent the barrel up at that point making the muzzle axis point lower if gas pressure was higher making faster bullets leave at a lower angle; slower ones with lower pressure leave at a higher angle.

As virtually all bullets are unbalanced, they'll all wobble, nutate, cone or in someother way fly through the air like a poorly passed football in the Super Bowl. A few fly perfect. All the rest wiggle as they fly. The more they wiggle, the more drag they have. With more drag, they slow down faster. So the wiggly ones drop less at a given range; they strike lower than faster ones. Their BC ain't all exactly the same. Sierra Bullets conducting time of flight tests has observed this. Their best match bullets have about a 1% spread in BC because of it. All bullet makers' bullets have the same problem; some to a greater degree than others. After a friend spun a bunch of bullets in a balance measuring tool and shot only those with perfect balance, they shot a1 inch or so 10-shot groups at 600 yards. Some of those bullets were so bad they flew out of the test collet spinning 30,000 rpm.

I don't know of anyone in the last several decades that's shot a given bullet through screens every few yards all the way to at least 500 yards to show how a single bullet prints relative to the line of sight at each range. If it's been done and there's a link to it, please post it.

About both vertical and horizontal group size, can anyone who can explain how a bullet at the right hand part of an aerial group at short range knows how to change direction to the left back towards the center of an aerial group at a longer range, each and every time it's in that place? Please elaborate.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master

Last edited by Bart B.; December 30, 2012 at 06:15 AM.
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