Like a friend once told me; all this information is giving me a sore head.
Is Spin Drift not by definition a form of instability caused by the location of the center of pressure in respect to the CG of long range bullets?
Is Pete’s bullet segregation not a form of quality control on the placement of the CG in order to maintain a consistent stable resistance of the mass in the barrel?
Ken
Nope and NOPE!!
"Spin Drift" is something a LOT more tricky........ and it will give you a headache! Here's a morsel to chew on.....
If two identical bullets are launched at identical velocities but different ROTATIONAL velocities... In other words one from say a 14" twist and one from an 8" twist. The bullet with the higher rotation will show a little MORE "spin drift". "Spin drift" is a function of wind. It's the same weird play of forces which causes leftward-drifting bullets to impact HIGH and rightward-drifting bullets LOW at the same yardage. Look at any wind chart to see this. With a highly accurate (Bench Rest accurate) rifle if you shoot a series of groups in a switchy wind and if you just hold center, the group formed will be tilted, not flat. The bullets "blown left" will impact high and visey varsey.... Here's a link to a thread which discusses this effect.
http://www.benchrest.com/forums/showthread.php?t=54001&highlight=wind+charts
NOW...... once you've digested this set of data then you can apply it to "spin drift".....
In perfectly calm air a bullet fired from a right-hand twist will drift to the RIGHT. This is because it IS being subjected to a "WIND" even though it's not windy. It's falling, accelerating downward at a rate of 32ft/sec/sec. And THIS is the reason that the effect is exponentially GREATER as range increases.......as the bullet falls further the "wind" against it's underside increases in force.... hence the increased rightward drift.
(((( Note here that although I've used the accepted "drift" this IS NOT really a drift function, it's a DRAG function. A STABLE bullet tries it's best to center on the wind vector just like a top on a table, it "stands up" on the wind vector that it sees. But it also precesses continually which results in the nose constantly fighting to escape at 90degrees AHEAD of the direction of rotation. This results in a NOSE DOWN attitude for a bullet flying in a R-to-L wind, a NOSE UP attitude for a L-to-R wind and a NOSE LEFT attitude for a bullet dropping through still air..... And you won't get this explanation from any ballistics text of which I'm aware
))))
So take it for what it's worth....
This is GOLD man.....
gottaheadache yet???
Ohh yeahhhh, and NOPE to Pete's deep seating thang.... the reason Pete seats deep (repeat .... the reason Pete seats deep...5 time FAST!) is to standardize the initial pressure curve. Super Accurate BR Rifles are "tuned" for accuracy by playing with the seating depth at the lands. By jamming HARD you eliminate or temper this variable.
al