Scope cant vs. coriolis + spin drift

Hellbender

Gunny Sergeant
Apr 23, 2008
1,114
3
38
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Lebanon, Missouri
#1
Been lots of talk lately about these factors, seems the paper punchers (F-class, Palma and BR) worry about it more than the steel shooters, as I believe the former shoot in more unknown conditions with quicker changing conditions between targets, therefore making these factors (apparently) disappear in the quickly changing "background noise".

ANYWAY....

It is something that IS ALWAYS there (and no-one disagrees on this) and it IS additive (for those of us with right hand twist bbls and shoot in the northern hemisphere).

The big quarrel is HOW MUCH, but I really don't care (loosely). If I can compensate (fairly closely) for it without having to think about it......what would be the disadvantages??

I can think of only a couple I'll bring up later.

So, here's what I did.....

I hung a 1/4" yellow rope from a tree limb at my range at 100 yards so I have a true vertical line.

I have a USO level on my gun (I don't see any way to do this properly without a level gun).

I canted the top of my scope to the left about .2 mil in 10 mils. (This is loosely what I have estimated my .308 178 gr @ 2730 fps @ 1000 yards has with drift and coriolis added)

I have a TMR reticule that the thin stadia lines subtend 10 mils (between the heavy top and bottom stadia lines), the heavy lines are .4 mils wide, so I put the bottom of the vertical thin line directly on the rope and canted the scope until the rope intersected the right side of the top heavy line, so I gained .2 mils in 10 mils. Rezero.

Took longer to explain it than do it. Very easy to see and to check.

If you disagree with the amount, just add more or less cant.

Now help me with the disadvantages......

1. Now you are slightly changing elevation as you adjust windage, is it enough to worry about? I never dial wind, so no downside to me.

2. If you don't have time to bubble level the gun, you may "eyeball" in a very slight cant. If it's a long range shot (say over 600 yards) I've usually got time to use the bubble level.

2 questions.....

1. Anything wrong with my method of adjusting the .2 mil in 10 mil cant?

2. What am I missing?

HB
 
Jan 6, 2008
686
1
16
Colorado
#2
Re: Scope cant vs. coriolis + spin drift

At 600 yards or even a thousand your talking about a 4 inch compensation (at 1000) So to me I would not cant my scope. If you get "sighter" shots in a competition it would not matter.It would personally bother me to have the cant in my scope. (I would notice it and want to adjust) because after years of shooting I would not be used to it. Plus if you fire in the opposite direction depending where you are on the earth your cant could me in the wrong direction. Maybe not for your spin drift but coriolis.
 

Hellbender

Gunny Sergeant
Apr 23, 2008
1,114
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Lebanon, Missouri
#4
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jimmy M40a2</div><div class="ubbcode-body"> If you get "sighter" shots in a competition it would not matter.

Plus if you fire in the opposite direction depending where you are on the earth your cant could me in the wrong direction. Maybe not for your spin drift but coriolis. </div></div>

We don't get sighters in the F-class and Tactical stuff we shoot.

Unless I am mistaken, the horizontal component of coriolis acceleration does not change in the northern hemisphere, only the verticle changes in relation to direction.

LL- PM sent.

 

BOLTRIPPER

Not Carlos Danger
Sep 25, 2001
5,540
70
48
Dallas Texas USA
#6
Re: Scope cant vs. coriolis + spin drift

i cant my scope ....it has more meaning for the .30 stuff out long....

i cant also for my .260....but...the higher BC bullets are more forgiving, and between wind and time limits and the way of the world....stuff seems to get lost...but if time is taken first round hits have been attained with ease out long.....

i know champions that sport a cant all the time on their stick
 

BOLTRIPPER

Not Carlos Danger
Sep 25, 2001
5,540
70
48
Dallas Texas USA
#7
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Skunk</div><div class="ubbcode-body">Does this have anything to do with the way the water goes when you flush the toilet, or are you guys just carving a rounder wheel?</div></div>

we don't have plumbing here in Texas.....
 

marduk185

take my karma boom
Feb 3, 2009
1,059
0
0
tantric thrust
#8
Re: Scope cant vs. coriolis + spin drift

okay maybe ill show some ignorance here but why would canting correct for coriolis, i thought it was a windage add or subtract dependent on which cardinal direction one faces at a given lattitude? help me understand this guys.
 

BOLTRIPPER

Not Carlos Danger
Sep 25, 2001
5,540
70
48
Dallas Texas USA
#10
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: marduk185</div><div class="ubbcode-body">okay maybe ill show some ignorance here but why would canting correct for coriolis, i thought it was a windage add or subtract dependent on which cardinal direction one faces at a given lattitude? help me understand this guys.</div></div>

cant for spindrift.....
 

The Mechanic

Gunny Sergeant
Sep 9, 2006
1,937
3
38
San Diego County Ca.
#11
Re: Scope cant vs. coriolis + spin drift

Coriolis depends on direction of shot and will be negligible unless you are shooting WAY past 1000 and are shooting north to south or south to north. And +1 cant for spindrift as this won't change as long as velocity (spin) changes. known distance targets with a spotter takes away all the above concerns though (cant, spindrift, and Coriolis).
 

milanuk

F'ing nuke
Mar 23, 2002
1,515
53
48
45
Wenatchee WA
#14
Re: Scope cant vs. coriolis + spin drift

I see *way* more talk about spin drift etc. on this site *here* than I do benchrest.com and long-range.com *combined*.

I'd dearly love to see the match bulletin for a Prone/F-Class match specifying *no* sighters.

Most of the ranges I've shot on... the small amount that spin drift, etc. contributes quickly gets rolled up into your wind dope and you move on. Most people I shoot with would look at you and just laugh if you started talking that stuff


Scope cant, on the other hand... is taken fairly seriously. Whether you shoot from a sling and use a fair amount of cant as part of your position, or from a rest (bipod or otherwise) and use no cant, as long as it's the same every shot, again, most folks don't worry about it too much beyond that. The sling shooters who do use a lot of cant may have to add a click or two of elevation for every so much windage they put on... fairly easily to sketch out on a piece of graph paper and figure out how much you need.
 

Hellbender

Gunny Sergeant
Apr 23, 2008
1,114
3
38
50
Lebanon, Missouri
#15
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DGosnell</div><div class="ubbcode-body"> I've never shot a F-Class match where there were no sighters. </div></div>

We actually shoot a "Modified" F-class from 100-700 yards with no sighters at Houston, MO. Prone with bipod, 5 shots at each distance.

 

Lowlight

HMFIC of this Shit
Staff member
Apr 12, 2001
27,257
3,042
113
Base of the Rockies
www.snipershide.com
#16
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: memilanuk</div><div class="ubbcode-body">I see *way* more talk about spin drift etc. on this site *here* than I do benchrest.com and long-range.com *combined*.

Most of the ranges I've shot on... the small amount that spin drift, etc. contributes quickly gets rolled up into your wind dope and you move on. Most people I shoot with would look at you and just laugh if you started talking that stuff


S.</div></div>

+1...
 

Hellbender

Gunny Sergeant
Apr 23, 2008
1,114
3
38
50
Lebanon, Missouri
#19
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: marduk185</div><div class="ubbcode-body">okay maybe ill show some ignorance here but why would canting correct for coriolis, i thought it was a windage add or subtract dependent on which cardinal direction one faces at a given lattitude? help me understand this guys. </div></div>

The horizontal (windage) aspect of coriolis is not affected by direction, only by how far you are from the equator, and if you are in the USA, it's pretty constant.

The verticle (elevation) is what's affected by the direction you shoot.

Here's a good read by someone who actually understands the theory behind it, unlike me, who only wants to shoot to the best of my ability....

http://www.appliedballisticsllc.com/index_files/SpinandCoriolisDrift.htm

The argument is over HOW MUCH it really affects it.

If you cant the reticule, as you add elevation clicks up, you are also adding windage (WITHOUT touching the windage knob) in incremental amounts.

In my case, it would be the same as:

Zero range (100 yd) it adds NO windage

@ 5 mils elevation it would add .1 mils of windage

@ 10 mils elevation it would add .2 mils of windage

Clear as mud?

HB

 

9H_Cracka

Gunny Sergeant
Mar 15, 2005
2,806
0
0
WAY off base (COS CO)
#20
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">[

We don't get sighters in the F-class and Tactical stuff we shoot.

</div></div>

Well then you aren't playing by the F-Class's sanctioning body rules.
 

Hellbender

Gunny Sergeant
Apr 23, 2008
1,114
3
38
50
Lebanon, Missouri
#21
Re: Scope cant vs. coriolis + spin drift

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: NineHotel</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hellbender</div><div class="ubbcode-body">[

We don't get sighters in the F-class and Tactical stuff we shoot.

</div></div>

Well then you aren't playing by the F-Class's sanctioning body rules. </div></div>

Sorry, they have been doing it there for years before I ever started shooting there, why don't you call them and file a protest, they have only been an NRA affiliated club for 30-40 years. I stated above they call it "Modified" F-class.

Whatever that has to do with this topic, could you please explain to me by PM instead of redirecting this thread off-topic??

Thank you,
HB