Spin drift on plates

[jambau]

When shooting steel at distance are you accounting for spin drift since you're looking for hits not bulls eyes?

 

[Bender]

Short answer: No

Long Answer: No

SD is still in the “noise” of the cone of fire.

 

[usafa77]

absolutely. Check you ballistics app.

 

[Gunfighter14e2]

Only time I account for drift is past 1K with high speed projo's, or anytime I'm shooting subs at distance

 

[Bender]

Maybe past 1200

 

[tna9001]

When shooting steel at distance are you accounting for spin drift since you're looking for hits not bulls eyes?

Here’s some good info on SD.

http://www.appliedballisticsllc.com/Articles/ABDOC108_GyroscopicAndCoriolis.pdf

 

[Darkside-Six]

No.

Only time i start considering it is past 1500. otherwise it gets lost in the mix of things. Wind is a far more important issue in my opinion.

 

[tna9001]

I don’t understand why guys dismiss SD, perhaps some solvers overstate the effect but the entire effort of long range shooting is eliminating as many variables and variations shot to shot as possible.

 

[SparkyHD1]

i thought this was a good video of how to sight in for spin drift

 

[Sheldon N]

i thought this was a good video of how to sight in for spin drift

What, the part where he had a left to right tailwind and claimed that it was all due to spin drift? Look at the paper on his shooting table flapping in the breeze.

 

[demolitionman]

first

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[tna9001]

i thought this was a good video of how to sight in for spin drift

Except the guy doesn’t understand SD. In the link I posted previously, Litz explains SD.

 

[cheapmoa]

SD is an easy calculation and correction. If you want to maximize your hit% then why would you not correct for it. Ballistic apps include it and at around .1 mil at 500 .2 mil at 1000 and .4 mil at 1400 it will definitely make a difference.

 

[Sheldon N]

I was shooting out at distance two days ago, in as near to no wind conditions as we ever get at our range. Proofing a new load (105 RDF at 2800fps), got first round hits on every target from a 6" at 525 yards to a 10" at 800 yards then an 80% IPSC at 950 then finally an IPSC at 1225 yards with three consecutive hits. I can tell you there was not 0.3 mil of spin drift at 1225 yards.

 

[cheapmoa]

How much SD did you have?

It is a simple calculation and my numbers were examples at sea level so yours might be .2 mil but it is definitely there even if you don't realize it.

Send me your density altitude and barrel twist and I can get you an exact correction.

 

[Sheldon N]

I know how to work the ballistic calculators and I know they say it's 0.3 mil based on the math. What I'm telling you is that doesn't match what I see when shooting. I shoot at that target all the time, with different guns, and in different conditions. There's just not 0.3 mil of spin drift. I've shot on DEAD days where it was pretty much straight up, maybe favor left edge. This is a 0.4mil wide target, you would notice 0.3 mil of drift. Not saying it doesn't exist, just saying it's not 0.3 mil at 1225.

IMO this is one of those things that's better experienced in practice than worked out in theory.

 

[SparkyHD1]

What, the part where he had a left to right tailwind and claimed that it was all due to spin drift? Look at the paper on his shooting table flapping in the breeze.

So your saying his ballistic app is incorrect and he shouldn't dial .9 moa for spin drift?

 

[_Windrider_]

So your saying his ballistic app is incorrect and he shouldn't dial .9 moa for spin drift?

Yes unless you are shooting 3 miles. I don’t use it or Coriolis. The simple fact is there is no way to calculate ite. It’s a SWAg at best and some calculators like AB just compound the problem by giving you a compounding flat rate. If SD was an issue we would all be using LH Twist barrels and eliminate it. Does it exist, yes. Is it something we have to concern ourselves with for our purposes (ELR and ULR excluded) not really. Maybe beyond transonic it’s an issue but that’s about it. Seriously. Turn it off and see what happens. I think you would be surprised. I was shooting 20 mph winds not accounting for SD and getting hits all the way out to 1425 with a 6.5.

.9 MOA (or do you mean mils) for SD at what range? At 1k, I only need 1 mil for a full value 20 mph wind with that same 6.5.

 

[cheapmoa]

I know how to work the ballistic calculators and I know they say it's 0.3 mil based on the math. What I'm telling you is that doesn't match what I see when shooting. I shoot at that target all the time, with different guns, and in different conditions. There's just not 0.3 mil of spin drift. I've shot on DEAD days where it was pretty much straight up, maybe favor left edge. This is a 0.4mil wide target, you would notice 0.3 mil of drift. Not saying it doesn't exist, just saying it's not 0.3 mil at 1225.

IMO this is one of those things that's better experienced in practice than worked out in theory.

So if I understand you correctly. You are shooting a .4 Mil target and holding left edge on a dead calm day. That would be .2 Mil of SD which depending on your Density Altitude is probably exactly right. If your ballistic app is saying .3 then it is probably a rounding error from .25 Mils.

Your description sounds dead on with what I experience as well for holding SD. You would miss half the time if you held center on that target.

 

[Deleted member 10043]

We miss half the time with or without it.

 

[cheapmoa]

We miss half the time with or without it.

Can't argue that fact. ?

 

[Sheldon N]

So if I understand you correctly. You are shooting a .4 Mil target and holding left edge on a dead calm day. That would be .2 Mil of SD which depending on your Density Altitude is probably exactly right. If your ballistic app is saying .3 then it is probably a rounding error from .25 Mils.

Your description sounds dead on with what I experience as well for holding SD. You would miss half the time if you held center on that target.

But I didn't miss when holding center of the target, even though the calculator gave a drift number in inches that was over half the target width. And keep in mind these SD numbers are not including the horizontal component of the coriolis force which at my latitude is roughly an additional 4 inches at 1225 yards (0.1 mil). My gut says that with the combination of SD and Coriolis I don't see more than half a target's worth of drift.

At the ELR match spending the weekend shooting with some of the best shooters in the counrty, know how many times I heard the words "spin drift" or "coriolis"? None. I turn them both off in my ballistics app.

You're not going to math the target into submission.

 

[RTH1800]

I shoot RF to 200 M on paper targets. It is definitely easy to view in that sphere, even at 100 M. I also see it beyond 600 M on a still day. Yes I correct for it but only off my actual data not an app.

 

[cheapmoa]

Every ELR shooter I work with uses corrections for SD but if you don't think it matters then that is your choice. My only point is that it is simple and exact so why not eliminate it as a variable.

http://appliedballisticsllc.com/Articles/ABDOC108_GyroscopicAndCoriolis.pdf

 

[cheapmoa]

But I didn't miss when holding center of the target, even though the calculator gave a drift number in inches that was over half the target width. And keep in mind these SD numbers are not including the horizontal component of the coriolis force which at my latitude is roughly an additional 4 inches at 1225 yards (0.1 mil). My gut says that with the combination of SD and Coriolis I don't see more than half a target's worth of drift.

At the ELR match spending the weekend shooting with some of the best shooters in the counrty, know how many times I heard the words "spin drift" or "coriolis"? None. I turn them both off in my ballistics app.

You're not going to math the target into submission.

Math is the only reason we can hit the target in the first place. Just because you have something else doing the math for you does not mean it doesn't exist. Take the app away from most shooters and change the density altitude and they become helpless at ELR. It has always been my preference to build calculations by hand so I have knowledge and context for my firing solution.

 

[_Windrider_]

Every ELR shooter I work with uses corrections for SD but if you don't think it matters then that is your choice. My only point is that it is simple and exact so why not eliminate it as a variable.

http://appliedballisticsllc.com/Articles/ABDOC108_GyroscopicAndCoriolis.pdf

No one disputes it’s real, but AB especially (of which I use frequently) overstates it. When I say turn it off, it doesn’t mean I don’t account for it in my wind holds. I gather dope on the wind and it’s built in. Problem with AB and many others is it compounds it. It adds too much because it’s using a linear equation for a non linear problem. If I’m hitting dead center at 1k with a 1 mil hold in 20mph winds, I’d say I have SD accounted for. Difference is maybe it’s only really .1 instead of .9 It’s just not as drastic as these BC’s state because it’s not being accounted for correctly in a point mass solver.

 

[cheapmoa]

No one disputes it’s real, but AB especially (of which I use frequently) overstates it. When I say turn it off, it doesn’t mean I don’t account for it in my wind holds. I gather dope on the wind and it’s built in. Problem with AB and many others is it compounds it. It adds too much because it’s using a linear equation for a non linear problem. If I’m hitting dead center at 1k with a 1 mil hold in 20mph winds, I’d say I have SD accounted for. Difference is maybe it’s only really .1 instead of .9 It’s just not as drastic as these BC’s state because it’s not being accounted for correctly in a point mass solver.

I use Coldbore but it has never been off by that much. I'll have to compare it to AB.

 

[Sheldon N]

Math is the only reason we can hit the target in the first place. Just because you have something else doing the math for you does not mean it doesn't exist. Take the app away from most shooters and change the density altitude and they become helpless at ELR. It has always been my preference to build calculations by hand so I have knowledge and context for my firing solution.

Fair enough. You're right about the math.

My two points are this. First, I believe the formula (which is an approximation) often over estimates spin drift, not that it doesn't exist. I'll quote Brian Litz himself from another forum post a couple years ago (emphasis added).

The approximate solutions for SG and spin drift are based on sound math, and they're much better than nothing. However they're far from perfect.

An example from my own spin drift testing.

We built two 308 Win rifles, similar in every way with exception of left vs. right twist barrels. We volley fired into a common point of impact 32" above the point of aim at 100 yards on a plumb line. This 100 yard volley fire insured the rifles were zeroed together, and the only difference in their point of impact at long range would be the difference in spin drift between the left and right twist barrels.

Two bullet types were tested.

175 grain Berger OTM
When 10-shot groups were fired from the two rifles at 1000 yards, there was 22.8" horizontal difference between the group centers. That means that each group drifted 11.4" from center. The calculated spin drift for this bullet in the conditions of the day was 11.2". Considering the group size and minor data scatter, this is a pretty close estimate for the calculation.

185 grain Berger OTM (Juggernaut)
Same procedure was employed for this bullet. In this case, the 1000-yard group centers were 6.7" left and right of center but the calculated spin drift was 8.8". So in this case, the formula missed the measured value by 2.1 inches. Wind was very low for both of these tests.

Full details of this test are published in Modern Advancements in Long Range Shooting - Vol 1, Chapter 12.

To wrap up our spin drift detour, I can say that the formulas available for calculating spin drift are approximations, and do not always agree perfectly with direct measurements.

Secondly, it's such a small order effect that most shooters are far better served to focus their attention on the primary issues like wind and fundamentals of marksmanship. This is why you have so many guys saying they don't worry about it.

This is more what I was trying to get at with my "math the target into submission" comment. It's the illusion that increased efforts in ballistic understanding are what will make you hit more targets. What will make you hit more targets is improving your wind call error and improving your overall abilities as a shooter. The assumption of having precision based off a detailed calculation of spin drift is akin to arguing about whether to put 20 year vs 30 year shingles on the roof, when the house is framed crooked and made of balsa wood.

 

[tna9001]

I use Coldbore but it has never been off by that much. I'll have to compare it to AB.

Pleas do, I’d be interested in seeing what the difference is.

 

[cheapmoa]

Pleas do, I’d be interested in seeing what the difference is.

Send me your input info and result and I will input it for cold bore and post it.

 

[tna9001]

Send me your input info and result and I will input it for cold bore and post it.

Will do, it will be later this afternoon before I ca send it.

 

[Darkside-Six]

I don’t understand why guys dismiss SD, perhaps some solvers overstate the effect but the entire effort of long range shooting is eliminating as many variables and variations shot to shot as possible.

I don’t understand why guys dismiss SD, perhaps some solvers overstate the effect but the entire effort of long range shooting is eliminating as many variables and variations shot to shot as possible.

According to my ballistics app, at 1000y spin drift will push my rounds .2 Mils right. That’s 10.8 inched. A 1 mph wind with have the same affect. I don’t know too many people that can read the wind down range all the way down to 1mph increments. It’s usulally a SWAG and they give it range (3-5).

Not arguing that SD doesn’t exist, it just gets lost in the mix of more important variables in my opinion.

 

[tna9001]

According to my ballistics app, at 1000y spin drift will push my rounds .2 Mils right. That’s 10.8 inched. A 1 mph wind with have the same affect. I don’t know too many people that can read the wind down range all the way down to 1mph increments. It’s usulally a SWAG and they give it range (3-5).

Not arguing that SD doesn’t exist, it just gets lost in the mix of more important variables in my opinion.

Well, it certainly is a small effect compared to wind but if we can identify the variable and correct for it then why not? Why do guys reload when they can buy factory ammo that gives a SD of 9-15fps? Because they can get a SD of 5 fps with reloading, its the small things that add up, unless you’re happy to just hit big pieces of steel or walk your shots to the target. Every variable that can be identified and accounted for is important, IMO.

 

[cheapmoa]

Well, it certainly is a small effect compared to wind but if we can identify the variable and correct for it then why not? Why do guys reload when they can buy factory ammo that gives a SD of 9-15fps? Because they can get a SD of 5 fps with reloading, its the small things that add up, unless you’re happy to just hit big pieces of steel or walk your shots to the target. Every variable that can be identified and accounted for is important, IMO.

I agree. We are looking for 1st Shot impacts. That is the true measure of expertise.

 

[Snuby642]

Can't see a good reason to turn it off in the calculator.
In 223 1/8 twist 16 inch tube 55gr 2900 fps my calculator gives a 1/4 moa shift starting at 165yds from a 100yd zero.
Can I tell on a windy day? No! can I ever hold 1/4 moa on a good day ocasionaly on a very good day not often to be truthful.
The calculator is just a starting point to save some ammo at the least at the best when dialed in more acurate than some can hold .
Why in hell would I turn functions off that have been proven?

You can let sd add up and get lost into your wind calls, I like to narrow my mistakes best I can.

Every click is holy, every click is good, we love every click in our naiborhood !

 

[CrazyHorse_mk14]

According to my ballistics app, at 1000y spin drift will push my rounds .2 Mils right. That’s 10.8 inched. A 1 mph wind with have the same affect. I don’t know too many people that can read the wind down range all the way down to 1mph increments. It’s usulally a SWAG and they give it range (3-5).

Not arguing that SD doesn’t exist, it just gets lost in the mix of more important variables in my opinion.

I was once told by a sniper fairie that SD is the same as a 1 mph wind. Never thought to check it with a calculator. The fairie was right ??!

 

[tna9001]

Send me your input info and result and I will input it for cold bore and post it.

According to the AB solver SD for the 147g ELD at 1500 yards is 19.44", at 1000 yards it's 6.12" and at 500 yards its 1.08".

I have shot to 1,000 several times in calm conditions and the SD calculation AB is giving was spot on.

 

[Snuby642]

I noticed your ballistic coefficient is set to 1 .
Is that normal?

Will ab run on an Android phone?

 

[tna9001]

I noticed your ballistic coefficient is set to 1 .
Is that normal?

Will ab run on an Android phone?

I'm using AB's custom curve that's why it shows 1.0. Out to 1,308 yards, which is as far as I've shot, the elevation hold is dead on with the custom curve.

The screenshot I posted is from AB's desktop version of their app which works on Windoz or Apple. Looks like they've got an app for Android:

http://appliedballisticsllc.com/products/apps/ab-mobile-app/

 

[cheapmoa]

COLDBORE

 

[rduckwor]

It's built in to my solver. Doesn't matter much until you get way out there.

RMD

 

[tna9001]

Thanks, cheapmoa, looks like AB and Coldbore are very close on the SD.