Those are terms used by the wiz kid's in here that really know way to much about bullets and such....way to complicated terminology for us common folk. Easiest way to spot one of thier type is look for the palm pilot and wind meter they also carry some type of a gadget for everything....You wont hear sounds like umm, hmm, or whaa?...they generally talk way to fast also.
I had to ask what ULD RBBT was....Sometime I feel the same as you, kinda like handing a 2nd grader a 12th grade algebra book. You know that dumb look you get?
Read the post on Parralax V/S Focus....It got me so darn confused that I now have trouble rembering what that knob is for.
I'd have to differ on the faster spin effecting terminal performance. Any centrifugal force of the bullet is kind of internal to that system, sure it takes a bit of frictional force to stop it in the terminal media, but that little bit of spin is insignificant to the terminal performance of the bullet when compared to the momentum.
No way was I gettin down on Blacko I was just admitting that I to sometimes have no idea what you guys are talking about.........way over my head! Just letting him know he wasnt the only one lost in space on the subject. We figure it out one day!
The best book I've read on it is 'Modern Exterior Ballistics' by R.L.McCoy.
This is not easy stuff to understand, or simplify. It is afterall, part of rocket science.
There is Greenhill, barrelmaker tables, and a few other rules of thumb out there. All will fail tests quickly, and some(like an nfa spreadsheet) are nothing more than monkey math. That is, they defined extremely narrow observations with math. Then put it out there as though it would work across the board. WRONG, anything outside that narrow window -falls apart completely.
Working on it for over 10yrs(very part-time), I have not been able to put together a rule of thumb which would pass all tests. I currently use McCoy's code(slightly modified) which also encompasses much of the math within JBM's calculators. JBM - Calculations
Even McCoy's math will not predict all. It will not pass ALL tests either. His testing was limited too, although not so much as for Greenhill. But it does take way more into account than ANY rule of thumb.
To perfect this area of science requires more testing, simple as that.
Well I'm not familiar with all of the units that Mikecr was using but I think I got the gist of what he was saying, and agree with it. So I'll take a stab at breaking it down barney-style
Basically displacement per turn shows the relationship between how much gyroscopic stabilization there is for how much drag there is.
Since we're dealing with a projectile that has a center of drag in front of the center of mass we must have more gyroscopic stabilization than drag force, which will cause the bullet to "tumble" or destabilize.
Since how much air the projectile displaced is proportional to the drag, and how fast it's spinning is proportional to it's gyroscopic stabilization, how much air the projectile displaces in relation to one revolution tells us whether the projectile is stabilized or not.
So, what that means is, the further from the center of drag the center of mass is (longer bullet), and the faster we push the projectile (more displacement/drag), or the higher the amount of drag on the nose of the bullet (frictional coefficient), the faster the bullet must be spun to stabilize it.
I think I got it right but if someone wants to correct me, please do.
(had to edit a couple times before it looked like my thoughts came out right)