Twist Directions?

[Bart B]

Wind drift, spin drift, magnus, and vertical coriolis remain the same with N/S hemispheres.
Two of these are tied to twist direction (spin/magnus), but magnus varies with wind, a variable beyond the question at hand.
Horizontal coriolis changes specific to NS hemispheres.

This leaves SPIN DRIFT and HORIZONTAL CORIOLIS,, one affected by twist, and the other affected by N/S hemisphere. Both variables in the question.

Their combination, if unaccounted for, would affect ACCURACY (which is defined with any single shot) from one hemisphere to the other.
And the amplitude of this combination is tied to twist direction.

I don't think accuracy is defined by a single shot. That shot can be anywhere in a many-shot group. If a rifle shoots zero MOA at any range, then a single shot will indeed define its accuracy. I don't know of any zero MOA barrels in any thing that they're fitted to that do that at any range.

But a single shot may be close to defining zero. A zero is the center of a group being at what you're aiming at; a fixed place on the target.

Therefore I claim accuracy will be the same in stable atmospheric conditions in both hemispheres. It was in my experiences on both sides of the equator.

 

[Mikecr]

You're just not getting this one Bart.
You need to step away from a competitive format and consider shooting that the rest of the world does. Especially here, given that it's a HUNTING site.

ACCURACY is defined with any single shot as measured from center of mark.
PRECISION is defined only through prescribed repeatability, and provided all shots are on paper.
Two completely different things

1/2moa of ACCURACY can be relied on to hit a 1moa target. This is +/- 1/2moa from MARK.
1/2moa of precision can be relied on to put multiple shots in a group no larger than 1/2moa, regardless of where the group is w/resp to mark.
Scoring combinations of the two(in competition) rarely correlate to hunting as we don't group shoot on animals. The ONLY shot that counts for us is the first.
Now there have been 'Groundhog shoots' that produce scored accuracy. But most mutate as the holders cave to competitive participant wishes(BR formats), and end up scored BR shooting -with tag-teamed guns.
I've also seen record groups from IBS/NBRSA that were not winning scores, and vice-versa.

There is a local accuracy contest here that draws in quite a few, some from other states.
It's simple; 200yd bull, sandbags on a single table, on your turn you take a single shot, if you hit your mark you go to the next round(back of the line). No other rules, no equipment rules.
The bulls are switched from 1" to begin, to 3/4", to 1/2" on certain round counts and the final round(if second of final two shooters) is decided by closest to center.
It takes all day, typically going 9-12 rounds, one winner takes all.
And this varying time between shots, becomes a great equalizer.

There is pretty much every type of gun competing here as we bring what we're proud of for one reason or another, and some really hold expectations of winning(many side bets).
There are purpose built BR guns in 6PPC, 30br, 6.5x47L, Dashers,, some of which winning guns in sanctioned shooting.
There is a gamut of hunting guns also, in no way designed for grouping, but some are accurate as hell.

I've seen 30brs/6PPCs here that can 'group' in the 1s at this range, on demand, lose to a plastic stocked Savage in 243Win.. And I doubt that Savage could hot group 1/2moa.
Over the years it seems like the winner cannot be predicted.
I've won it, and lost it. I work with a 3-time winner, and talked to other winners. What I see common is an understanding that precision and accuracy are completely different. And of course, great efforts towards accuracy -rather than precision.

Accuracy, with any gun, takes a lot of work. You can't just cut checks for this.
Now you can generalize single shot accuracy over multi-shot accuracy or whatever. But don't confuse them, or what we need for LR hunting.

 

[Bart B]

You're just not getting this one Bart.

Yes I do get it. But we have a different opinion of what accuracy is. I well understand your point of view. I can accept that. Mine's different. Maybe you can't accept that.

 

[rscott5028]

I kinda' agree with BartB on this one.

The rifle's accuracy will be as consistent and predictable as it is regardless of where you shoot notwithstanding environmental conditions.

If spin drift, corriolis, magnus are sufficient to affect POI for a kill shot, then you're going to need a computer to solve the equation. So, it won't matter whether you input a right hand or left hand twist rate.

If you're relying on a swag and/or Kentucky windage, then a lucky rabbit's foot will do just as good.

-- richard

 

[Mikecr]

Well, at the risk of seeming stubborn, I already got the cigar and I ain't giving it back

 

[rscott5028]

Well, at the risk of seeming stubborn, I already got the cigar and I ain't giving it back

and deservedly so

congrats!

-- richard

 

[kranky]

I would be more concerned with crosswind drift and wind drift with a left twist considering nearly all modern barrels are RH twist. Being in the military and deploying to different regions has led me to believe that a level scope with the paralax properly adjusted, a solid weapon platform, a solid cartridge, and a compitent rifleman is far more importent than factoring in the fact that the earth is rotating and what hemisphere I am in. An accurate wind call is hard to find when shooting past 12-1500yds. All i'm saying is that i've seen( and had myself) more missed shots from a poorly judged wind call (at the distances we would need to factor in earth rotation and position) than coriolis and hemisphere corrections. The definitions in the above posts are in fact correct, I was pleasantly suprised as I am new to the board and have heard some interesting post on this subject in the past. If anyone wants another good read (other than Litz's) check out "Understanding Firearm Ballistics" by Robert Rinker. It's a bit dry but a great read for any bullethead.