Best Spin Drift online calculator?

[BrentM]

I realize I can add "purt-near" spin drift info to my rifle's taped on drop table but I need something that will give me exact drift to 1,100 yards for both 6.5 CM and 6.5 PRC with MY muzzle velocities.

I haven't yet purchased a Kestrel 5700 4DOF weather meter so I just need something online and free or cheap.

Eric B.

Hornady has nice free on line program.

Personally I spend a little extra and get an app for the phone, like AB or shooter. They are cheap and you can play around anytime with the phone and run different situations to see the effects of ammo, environment etc.

Spin drift is not linear but for your rifle it is about .25 at 500, .6 at 1000 and .7 at 1100.

I don't mess with spin drift in the .1 range. For example 500 and less I don't care. 500-1000 I'll consider wind and add .5. 1000-1500 is .75. 1500-2000 is 1 moa. To get rid all this bs I zero .5" left and never mess with spin drift to 1000.

 

[User4302021]

Most programs don't actually calculate spindrift. They just plug in an average. If you run a solution with a fast twist, and then run it again with a slower twist, and the solution doesn't change...then you know it isn't actually calculating spindrift specifically for your rifle.

 

[BrentM]

Most programs don't actually calculate spindrift. They just plug in an average. If you run a solution with a fast twist, and then run it again with a slower twist, and the solution doesn't change...then you know it isn't actually calculating spindrift specifically for your rifle.

Never seen a decent app not calculate SD. I have 3 on my phone, looked at others, and they all do. I do see people not correctly setting up the ammo profile which disables the program.

 

[User4302021]

Never seen a decent app not calculate SD. I have 3 on my phone, looked at others, and they all do. I do see people not correctly setting up the ammo profile which disables the program.

Which ones you using?

 

[BrentM]

Which ones you using?

Shooter, applied ballistics, ballistic ae, arc, strelock. I have Hornady app on my phone too, just don't use it much. Shooter does everything I need except wind segmenting. I've become decent enough at wind I don't need it unless just modeling.

 

[User4302021]

Well, all I can say is this...

When I run something like a 300 Winmag in AB, at 1500 yards it gives me 0.4 mils spindrift with a 1/10 twist...If I run the same simulation with a 1/8 twist, it only gives me 0.5 mils.

Does that seem reasonable to you? To go from a very conventional 32 calibers per turn, to a fairly radical 25 calibers per turn, and only get a 0.1 mil difference at 1500 yards?

I might be wrong, but I don't think so. Not based on what I've seen.

Another experiment with AB...run a cartridge that is a known combination. Label it what it is 6.5 Creed, 300 Win,...whatever. Then record data with two different barrel twists.

Then, load the exact same profile for another rifle, but call it "Random" and run the same simulation. I bet you get a different solution.

I'm not bashing AB or any other program. I have them, I use them, I'm grateful for them. But all is not as it seems.

 

[BrentM]

Yes, that is reasonable. The difference is not that great unless you increase FPS as well.

Some people will try and map SD for their specific rifle and ammo combo. This is very difficult to do since you have environmental conditions influencing the outcome as well. I have seen very little difference in 1 caliber and velocity to another. Different twist rates etc. That is why generally speaking you can use .25/500, .50/1000, .75/1000-1200, 1 moa/1200-1400, 1.5/1400-1600, etc.

 

[dfanonymous]

Yes, that is reasonable. The difference is not that great unless you increase FPS as well.

Some people will try and map SD for their specific rifle and ammo combo. This is very difficult to do since you have environmental conditions influencing the outcome as well. I have seen very little difference in 1 caliber and velocity to another. Different twist rates etc. That is why generally speaking you can use .25/500, .50/1000, .75/1000-1200, 1 moa/1200-1400, 1.5/1400-1600, etc.

You're right about SD not being linear. I answered the OPs question about the to calculate it, as kestrel generally uses litz formula, I didn't go into depth about how it's widely it's considered wrong. Not just by the peanut gallery but by litz himself. It's under the theory that, the issue of SD is there, so something must be done to calculate it, but something is not necessarily better than nothing. Really most cartridges are going to be spun around 2-6 inch at 1k. You'd be more "correct" holding or adding subtracting .1 mil from your over all solution to address it. Or you'd be closer using 2% of your drop to calculate for further out. There is substantial 6 dof data that shows that the solutions built into all calculators is incorrect and the incorrect data only appears more and more evident the further out you go. However the appeal is generally to those that want to input and forget the issue, or simply aren't aware.

 

[BrentM]

You're right about SD not being linear. I answered the OPs question about the to calculate it, as kestrel generally uses litz formula, I didn't go into depth about how it's widely it's considered wrong. Not just by the peanut gallery but by litz himself. It's under the theory that, the issue of SD is there, so something must be done to calculate it, but something is not necessarily better than nothing. Really most cartridges are going to be spun around 2-6 inch at 1k. You'd be more "correct" holding or adding subtracting .1 mil from your over all solution to address it. Or you'd be closer using 2% of your drop to calculate for further out. There is substantial 6 dof data that shows that the solutions built into all calculators is incorrect and the incorrect data only appears more and more evident the further out you go. However the appeal is generally to those that want to input and forget the issue, or simply aren't aware.

It doesn't get the attention it deserves unless shooting ELR. That crowd has to address a lot of different issues the 1500 and less shooter deals with. For the average long range shooter sd is a non-event. Under 1k, the calculators get close enough that the avg shooter would never be able to add any value. Most people are dealing with environmentals that considerably more devastating to precision.

 

[Canhunter35]

I really appreciate you guys adding some depth to the conversation.
It's making much more sense why tof makes such a difference in sd than I ever realized. Need to drag my 7mm out again, cause inside 1000, sd seems almost negligible compared to my 308

 

[dfanonymous]

I really appreciate you guys adding some depth to the conversation.
It's making much more sense why tof makes such a difference in sd than I ever realized. Need to drag my 7mm out again, cause inside 1000, sd seems almost negligible compared to my 308

To be clear, since you have some interest, this is under the assumption that the litz formula is correct. Which it's not in all cases. Litz's formula is of linear value, as discussed above, SD is not linear. This is a complex topic that in even the best of math equations still contain at the least a a certain % of error. Hornady 4dof uses a flat rate. Also a linear equation. This is also not correct. These are based on TOF but with a over lapped flat rate value. Simply put theres more to the equation. Hence why 1% to 2% of drop is a little closer to reality. I'll link below as to why.

It's a over all complex subject if you aren't a nerd. If you are then here's some material:

https://www.researchgate.net/profil...-and-Spin-Drift.pdf?origin=publication_detail

 

[User4302021]

Jim Boatwright's paper is what opened my eyes to it.

It was through conversations with him on another site that he dropped the knowledge bomb that, based on his extensive analysis of the military small arms PRODAS data he had access to, "...For any given combination, spindrift is some invariable percentage of drop".

He went on to say that for the vast majority of combinations, that percentage falls between 1% and 2%.

I believe that what Hornady has done in thier program is use a flat rate, but they have cut it down the middle at 1.5%. Litz's program, as well as most others hover between 2.5% and 3%. That is the main reason I leave both spindrift an coriolis turned off on whatever program I am using, and dial it myself. I typically use 1% and round up to the nearest 0.1mil increment.

 

[Danehunter]

df,
I was re-reading your 1st response regarding the fact that most ballistic "engines" miscalculate spin drift at extreme ranges.
My question is why the he11 can't it be figured out with all the Doppler radar and super computers available. Surely the military has a hand on this for long (read REALLY long) range artillery.

I get it that given the attitude of the bullet relative to the ever-increasing arc of flight, decrease in velocity, transonic shift meddling with all this, etc. are problems but at least we know what 95% of the problems are.
Perhaps the sacrifice of deer liver or reading elk entrails would help with the problem.

Eric B.

 

[BrentM]

df,
I was re-reading your 1st response regarding the fact that most ballistic "engines" miscalculate spin drift at extreme ranges.
My question is why the he11 can't it be figured out with all the Doppler radar and super computers available. Surely the military has a hand on this for long (read REALLY long) range artillery.

I get it that given the attitude of the bullet relative to the ever-increasing arc of flight, decrease in velocity, transonic shift meddling with all this, etc. are problems but at least we know what 95% of the problems are.
Perhaps the sacrifice of deer liver or reading elk entrails would help with the problem.

Eric B.

Just an opinion but usually things have to be so far off the precision chart that reliability is at zero before something gets attention. I'm not that versed in elr but have spent a little time with some who do it for comp and this isn't a big issue. They generally calculate with kestrel or another app I can't recall the name of and tweak the data. The problem has always been overcoming other atmospheric factors. Also since sd has a pressure differential problem not all projectiles have a predictable solution. I think it's because the designs are so different that it's overly complicated