Zeroing for Spin Drift

[Antares]

Does anyone zero a little left to account for some spin drift?

My solver tells me I have 1/4 MOA of spin drift at 500 yards, but in practice it seems closer to 1/2 MOA (I'm shooting an 8 twist 6.5CM). If I hold on the center of a 10" plate I consistently hit on the right third of the plate. If I hold on the left third of the plate I hit the center. If I'm shooting clay pigeons I have to hold off the left edge to break them (again at 500 yards). This is after many sessions, different conditions, different zeros (rezeroing after working on the rifle, etc.).

So, I'm thinking I should zero a 1/4 MOA left at 100 yards as a compromise to take out some of this drift. Anyone do this?

Let me head off some distractions..."you can't shoot good enough groups for it to matter", "you can't call wind good enough for it to matter", "you can't zero your rifle good enough for it to matter", etc... Ok, probably not, but for the sake of discussion, let's assume I can.

Thanks for your insight!

 

[ButterBean]

I zero dead on at 100 and verify spin drift from there

 

[hereinaz]

If I can't get a perfect zero, I shade it left. Spin drift is minimal at most hunting ranges, but I leave it on in AB.

My crappy wind call is the problem, lol

 

[mt100gr.]

If I can't get a perfect zero, I shade it left. Spin drift is minimal at most hunting ranges, but I leave it on in AB.

My crappy wind call is the problem, lol

This. I err to the left if that's where my zero needs to be otherwise I consider the correction from AB and account for it WITH my wind correction. I also break my dope charts down into increments that fit my scope (1/4 MOA) so a 0.4 correction becomes .5 MOA. Again, erring in favor or that minor factor that is spin drift. .....then I cuss the wind and practice reading it better.

 

[hereinaz]

This. I err to the left if that's where my zero needs to be otherwise I consider the correction from AB and account for it WITH my wind correction. I also break my dope charts down into increments that fit my scope (1/4 MOA) so a 0.4 correction becomes .5 MOA. Again, erring in favor or that minor factor that is spin drift. .....then I cuss the wind and practice reading it better.

I don't cuss, but I mutter under my breath at the wind...

 

[huntnful]

I do. For hunting purposes. 1/2 MOA left. Which puts me just a hair right at 800 yards and well inside any kill zone closer than that. I think if I was strictly target shooting, I'd zero center at 100 and correct for it at a given distance. But for just in the field hunting, it's one less thing I need to think about.

 

[Antares]

I do. For hunting purposes. 1/2 MOA left. Which puts me just a hair right at 800 yards and well inside any kill zone closer than that. I think if I was strictly target shooting, I'd zero center at 100 and correct for it at a given distance. But for just in the field hunting, it's one less thing I need to think about.

Thanks for the input. It seems like a pretty straightforward idea, but I could found very much info on it. I should've clarified that I'm talking about hunting, not target shooting.

 

[CentralFLMike]

Have you ruled out rifle cant?

 

[Antares]

Have you ruled out rifle cant?

I have not considered this. I think I’m pretty plumb. Would a right handed shooter be likey to be canting in a way that results in impacts to the the right?

 

[PathFinder]

Can be rifle cant or a scope that doesn't dial plumb.
Why try to zero for spin drift when it's quantitatively insignicant? Compared to wind drift and target size, it's almost entirely meaningless. It's just factored in with the wind call and accounted for without considering it separately.

Sent from my SM-G973U using Tapatalk

 

[AZ_Hunter_2000]

I have not considered this. I think I’m pretty plumb. Would a right handed shooter be likey to be canting in a way that results in impacts to the the right?

If you come into the rifle from the right instead of directly from behind, it’ll move to the right. Only takes a slight amount of cross pressure to move the POI. This becomes more noticeable the further you shoot.

If you have someone else shoot, that has sound fundamentals, do they get the same results?

Had this issue but was coming in slightly from the left.

 

[MaraviaDave]

Does anyone zero a little left to account for some spin drift?

My solver tells me I have 1/4 MOA of spin drift at 500 yards, but in practice it seems closer to 1/2 MOA (I'm shooting an 8 twist 6.5CM). If I hold on the center of a 10" plate I consistently hit on the right third of the plate. If I hold on the left third of the plate I hit the center. If I'm shooting clay pigeons I have to hold off the left edge to break them (again at 500 yards). This is after many sessions, different conditions, different zeros (rezeroing after working on the rifle, etc.).

So, I'm thinking I should zero a 1/4 MOA left at 100 yards as a compromise to take out some of this drift. Anyone do this?

Let me head off some distractions..."you can't shoot good enough groups for it to matter", "you can't call wind good enough for it to matter", "you can't zero your rifle good enough for it to matter", etc... Ok, probably not, but for the sake of discussion, let's assume I can.

Thanks for your insight!

If you’re impacting 1/2 MOA (2.5”) left at 500 yrds.....that’s most likely indicating a problem with your fundamentals. It’s impossible to diagnose the issue, without watching you shoot, so a couple of questions for you to consider. 1) are you square behind the rifle? Spine parallel to the axis of the bore? Shoulders perpendicular to the recoil pad? 2) are you applying a lot of pressure on the stock through your cheek weld? If so, lighten up on your cheek weld. 3) are you slightly loading your bipod? Does your bipod have a panning feature? If so, is it tight/locked out? 4) is your thumb wrapped around the stock? If so, are you sympathetically squeezing your hand around the grip as you pull the trigger? 5) are you checking your natural point of aim (NPA) prior to making the shot? 6) is your trigger finger 90 degrees to the trigger? 7) are you slapping the trigger? 8) have you focused your ocular? 9) are you properly adjusting for parallax? 10) what is the height of your group in comparison to the width?
Applied Ballistics uses a flat rate number, for Spin Drift based on bullet time of flight (TOF). This is an oversimplification for how to determine SD. Over the years AB / Brian Litz has lowered the flat rate number they use.....many would argue that it’s still too high. Until you get out to 1,200 + yards, there are more important things to focus on......Like dry firing.

 

[CentralFLMike]

I have not considered this. I think I’m pretty plumb. Would a right handed shooter be likey to be canting in a way that results in impacts to the the right?

In addition to making sure the bore and crosshair are plumb with gravity, ones grip has a lot of influence on rifle cant. I was taught to place my thumb straight forward along the ridge of the stock instead of placing it over the rear and gripping it, which causes torque. A properly mounted level can help fight cant.

 

[Antares]

If you’re impacting 1/2 MOA (2.5”) left at 500 yrds.....that’s most likely indicating a problem with your fundamentals.

I’m impacting right at 500 yards, in case that changes your assessment.

I appreciate your detailed response. The only thing that stuck out to me on your list is my cheek weld. I would call it “solid.” Maybe I could lighten up a little.

 

[Lawnboi]

Run a tall target test at 100 yards to rule out cant on the reticle/tracking

 

[Antares]

Run a tall target test at 100 yards to rule out cant on the reticle/tracking

Sounds great. Send me a box of ammo. I shoot the 140 ELDM.

Just kidding.

 

[huntnful]

Sounds great. Send me a box of ammo. I shoot the 140 ELDM.

Just kidding.

lol, 2 1/2" is pretty far right at 500 to be SD. But not necessarily in general. Could be your fundamentals or tracking. If you're printing good groups, just slightly right, I'd just bump it 1/2 MOA left and call it good. If you want to really get down to the details, you need to plumb everything up and do a tracking test. I wouldn't shoot at anything past 500 yards with a 6.5 creemoor anyways, so if that's your max yardage, I wouldn't burn up ammo and time moving everything around and having to resight in. If you want to stretch the legs for target shooting though, go back to square one with making sure everything is perfect and plumb and tracts accordingly.

 

[Lawnboi]

Sounds great. Send me a box of ammo. I shoot the 140 ELDM.

Just kidding.

It’s sick what they are charging for that stuff now.

 

[khuber84]

Simple spin drift solution if everything on the rifle is dead nuts is zeroing a 1/3" left of bullseye at 100y. Since your scope likely has 1/4 clicks, you choose 1/4 or 1/2".

 

[Antares]

Simple spin drift solution if everything on the rifle is dead nuts is zeroing a 1/3" left of bullseye at 100y. Since your scope likely has 1/4 clicks, you choose 1/4 or 1/2".

Thanks. this is where I ended up. I just zeroed a 1/4 MOA left and forgot about it. Once my range thaws out in a month or so I'll start shooting again and see how it works for me.