i have been trying to find more info on spindrift. Is there any way to predict it or figure it out
Spin drift
- Thread starter freebird63
- Start date
here
http://www.jbmballistics.com/ballistics/calculators/calculators.shtml
the "trajector -drift" calculator will calculate spin drift
http://www.jbmballistics.com/ballistics/calculators/calculators.shtml
the "trajector -drift" calculator will calculate spin drift
Depart123
For traditionally stabilized bullets at 30 calibers per turn or more, I use 2% of drop. For faster twists of 28 calibers and less, I use 1% of drop.
huhh?
Please a'splain......... you're saying the angle of the yaw of repose of a faster rpm bullet is LESS than that of a bullet spun more slowly?
And how does a normal person figure "drop?"
XTR
F-TR obssessed shooting junkie
Yes, spin drift is caused by the spin on the bullet from the rifling. Coriolis is from the earths rotation. I've never considered coriolis in a shot.
Spin drift will come into play shooting at 1000 yards on an F class target when you get a wind that is fishtailing (i.e, switching left to right). If you are shooting with a 100 yard zero then at 1000 yards your no wind zero is ~½ to 3/4 MOA left of your 100 yard zero. In a Fullbore match where you can't wait for your condition to come back and you have to make the wind call shooting at a 1MOA 10-ring that is enough of an error to cost you a point if you haven't accounted for it.
Just for example. You have a wind from your left, you've taken your sighters and you need 1MOA left to be centered up shooting 10s/Xs and the wind crossed over to the right. If you weren't accounting for your spin drift you actually had ¼ to ½ left on. The wind crosses over, and the wind looks about the same as the wind you were just shooting in but from the right, so you put on/hold 1MOA right, except now that ½ to 3/4MOA is added to your dope, not subtracted, and you've got 1 ½ to 1 3/4 right on in a wind that only needs ¼ to ½. You are lucky if you don't end up in the 8 ring.
Advice, For us old folk that can't remember, would it be better to put the spin drift into our zero, another words our 1000 wind zero is including the calculated spin drift. Thanks
Depart123
I don't figure drop, my ballistics program tells me, or I shoot it to find out, you know, 3.1 mils at 500 yards....10.1 mils at 1000yards etc..
As for the rest, you can read the paper on coning theory by Jim Boatwright yourself.
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I don't agree with Boatwright much, since he disagrees with Vaughn, Rinker, McCoy et al. Especially on things like coning angle, nutation and yaw of repose. Heck, even the "Sierra Techs" useta' disagree with the real ballisticians but they rewrote their books a couple yrs ago because of controversy (and the fact that they were wrong lol...) Boatwright still tries to "prove" everybody else is wrong.......
Regarding your first part about "I don't figure drop"...... that's just meaningless unless you actually DEFINE something as datum. Boreline? LOS? 100yd zero? 1000yd zero???
"3.1 mils"
"10.1 mils"
From WHAT??
From what reference?
I get to paraphrase FGuffeY here...... "numbers are meaningless without a reference"
Depart123
You just gotta be THAT GUY huh?
Coriolis is from the earth spinning..... picture yourself standing on a big record player turntable and rolling a ball. Coriolis drives the bullet path to the RIGHT in the northern hemisphere. Always. But only 2-3 inches at 1000yds (and actually, it's the earth moving out from under...)
"spin drift" is actually a drag function. A bullet is dragged by it's tail. Basically wherever the tail points it is driven that way by deceleration. So when a bullet points it's nose INTO the wind (this is what a bullet does, regardless what Boatwright sez) it's tail is pointed down-wind so it's dragged downwind. And due to something called "yaw of repose" it's not point EXACTLY into the felt wind, it's got some lag. This slight lag orients the butt of the bullet just slightly "right" of the felt wind. In the case of wind on a bullet, "right" is UP in a right/left wind and DOWN in a wind from left to right so bullets blown to the left hit high and bullets blown to the right hit low. (Again, these are FACTS not Boatwright's opinions. Real scientists took pixtures even, to "prove" the math....)
A forward moving but falling bullet has a wind on it's belly.
The wind on it's belly means it's dragged to the RIGHT 8"-10" at 1K
Now, can we SEE IT?? Dunno.... II don't know if I can.
Between the two I figger 4" right at 600 and 12" right at 1000 but I can't really observe it.
I shoot in my own yard.
About 15yrs ago we were shooting 1000yds on an absolutely perfect evening. We could spot "wishes" in the air for a half mile and the whole air mass was nearly static. We THOUGHT, we BELIEVED that that day we actually observed "spin drift" but today, having spent 25yrs trying to even find a "dead-air zero" with limited success........ I no longer believe we saw it.
Others' experience will differ but that's been mine.
not sure what that means but I do enjoy facts
opinions, not so much
but I will shut up now....... it took me a while to work up the seeds to post this on this pertickler forum, I shall now withdraw forthwith
sorry to have stepped into your room
Geez, I enjoyed the explanation. I too love facts, having been in Law Enforcement for 37 years I lived with facts. You didn't step on any toes at all, and as I am the OP here, I get to decide who can stay.not sure what that means but I do enjoy facts
opinions, not so much
but I will shut up now....... it took me a while to work up the seeds to post this on this pertickler forum, I shall now withdraw forthwith
sorry to have stepped into your room
Depart123
So you bust into a thread...stomping dicks....and I'm the asshole?
When can we expect your peer reviewed papers on this matter?
So you bust into a thread...stomping dicks....and I'm the asshole?
When can we expect your peer reviewed papers on this matter?
now you can't delete it once you sober up
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