Range Report "X MPH Gun" wind info/rules

[ItsChippendale]

Hopefully I didn't miss where this was clearly stated in other posts;

I'm trying to find some more information on the "mph gun" wind technique. From what I understand you get the G1 BC of the bullet and multiply it by 10, and that is the Mph you base your chart on. I.e 175 SMK G1 BC = .474 x 10 = 4.7mph gun or 4.5mph gun for a easier number. Then if I'm correct the chart would as follows:

@ 4.5 mph
100yds = 0.1 mil
200yds = 0.2 mil
300yds = 0.3 mil
400yds = 0.4 mil
500yds = 0.5 mil
600yds = 0.7 mil
700yds = 0.8 mil
800yds = 0.9 mil
900yds = 1.0 mil
1000yds = 1.1 mil

Then if you have a 9 mph full value wind @ 500yds you double your value i.e 0.5 mil @ 4.5mph x 2 = 1.0 mil @ 9mph. Seems straight forward so far?

My question is if there's any flaws with what I understand so far? What about past 1000yds, are there any other jumps like there is at 700yds? Anything else that I'm missing? And lastly if station pressure or different muzzle velocity ranges have a effect of this, if so what are the fps standards for what mph range, and how do we account for these exceptions? Thanks guys

 

[Lowlight]

There are jumps and the conditions will matter too, but you basically have it.

There are differences, you'd need either real-world data or once your software matches this number you can memorize it, basically, you are taking the two methods, software and this, lining them up and using the trends software will highlight.

 

[ItsChippendale]

There are jumps and the conditions will matter too, but you basically have it.

There are differences, you'd need either real-world data or once your software matches this number you can memorize it, basically, you are taking the two methods, software and this, lining them up and using the trends software will highlight.

Thanks for the info/validation Frank, I've been listing back on some of your older podcasts on the issues and picking up what I can out of them.

 

[FishDr]

I have recently started using this method to get an initial wind call and adjust from there. As pointed out above, the data needs to line up with actual observations / software. For instance, when I put 5.7 MPH in my ballistic app for the 260 Rem, I learn that this initial wind call is correct to 800 yards. My “jump” in data happens at 900. IE 800 in 5.7 mph = 0.8 hold off, 900 in 5.7mph = 1.0. Just be sure to validate.

 

[ItsChippendale]

I have recently started using this method to get an initial wind call and adjust from there. As pointed out above, the data needs to line up with actual observations / software. For instance, when I put 5.7 MPH in my ballistic app for the 260 Rem, I learn that this initial wind call is correct to 800 yards. My “jump” in data happens at 900. IE 800 in 5.7 mph = 0.8 hold off, 900 in 5.7mph = 1.0. Just be sure to validate.

Yeah I wanna pay more attention to what my initial wind hold should be, usually I use what my kestrel says but I never payed a ton of attention to validateing wind holds like I do elevevation data. So if my kestrel said 0.8R I would mentally think "0.8R but your metaphorical mileage may vary" lol but I want to start using a more systematical approach to my wind holds, thanks for the input tho

 

[Deleted member 113831]

The "base wind" of a particular bullet varies by the velocity and the altitude you are operating at.

2,800 fps is your base velocity. If your bullet is around 2,600 fps you will need to drop your base wind by 1 mph. 200 fps equals 1 mph change.

2,000 ft is your base altitude. 4,000 feet up or down will equal another 1 mph change.

Changes can be either offsetting or compounding.

 

[ItsChippendale]

The "base wind" of a particular bullet varies by the velocity and the altitude you are operating at.

2,800 fps is your base velocity. If your bullet is around 2,600 fps you will need to drop your base wind by 1 mph. 200 fps equals 1 mph change.

2,000 ft is your base altitude. 4,000 feet up or down will equal another 1 mph change.

Changes can be either offsetting or compounding.

So personally I run a 6.5CM with a 130gr JLK @ approx 3050fps. So I would be at a 7mph base instead of a 6mph?

 

[Deleted member 113831]

So personally I run a 6.5CM with a 130gr JLK @ approx 3050fps. So I would be at a 7mph base instead of a 6mph?

The BC I found for that bullet is .620 G1, so yes, it would be a "7 mph" gun with that load. That is assuming an altitude of 2,000 ft.

 

[ItsChippendale]

The BC I found for that bullet is .620 G1, so yes, it would be a "7 mph" gun with that load. That is assuming an altitude of 2,000 ft.

Now the 2,000 ft rule, if you're at -2k the mph would drop and if you're at 6k the mph would increase I assume?

What about the different jumps you get the further you go out, are there standards, or is there too many variables to have fast standards for those?

 

[Deleted member 113831]

If you shot the same load at 6k ft, then you would have an 8 mph gun, at sea level a 6.5 mph gun.

The number works really well to 1K yards. With some combos you might get it to stretch to 1200 Yards. After that it starts to deviate fairly quickly.

It isn't exact anyway, it is just so close that the difference per 100 yards to 1K yards is inconsequential.

 

[ItsChippendale]

So for the sake updating the "rules" for everyone looking at it, here's what I have so far with some example:

“X mph Gun” Info/Rules

Standard Elevation = 2000ft ASL
Standard Velocity = 2800 fps

For every 200fps increase your mph increase by 1 mph, and vise versa.

For every 4000ft increase in elevation your mph increases by 1 mph, and vise versa

To determine your “base” mph multiply your G1 BC x 10

Example: G1 BC of a 75gr ELD-M = 0.464(Litz) x 10 = 4.64 mph

Now 4.6 mph is correct for 2800 fps @ 2000ft asl. Now for 2950 fps @ 1000 ft asl

Example: 150 fps increase / 200 fps jump per 1 mph = ¾ mph increase

1000 ft decrease / 4000 ft jump per 1 mph = ¼ mph decrease

So adding it all together we get:
4.64 mph + ¾ mph - ¼ mph = 5.14 mph

You then can choose to round to 5 mph for fast and easy numbers.

Now the standard numbers for any giving mph range is

100 yds = 0.1 mil
200 yds = 0.2 mil
300 yds = 0.3 mil
400 yds = 0.4 mil
500 yds = 0.5 mil
600 yds = 0.6 mil
700 yds = 0.7 mil

*past 700yds varies based on calibers, so use real world numbers and ballistic calc to help determine how it lines up past that

So those values on the same bullet from before would be true at 5 mph.

Now for crosswind constants:

Full Value = 1
¾ Value = 0.9
½ Value = 0.7
¼ Value = 0.4

So for another example: if we have a 12 mph, ¼ value wind @ 700 yards

12 mph x 0.4 (¼ wind constant) = 4.8 mph

So you would use your 700 yard 5 mph wind value hold of 0.7 mils.

*(The 0.2 mph will be impossible to account for because wind is a fluid and nobody is capable of shooting a noticeable difference that the 0.2 mph could give in theory so we ignore it)

 

[Quest1000]

Thanks for taking the time to consolidate the info! It really helped to clear a few things up for me.

 

[ItsChippendale]

Thanks for taking the time to consolidate the info! It really helped to clear a few things up for me.

No problem, I also tend to lose track of info when it's scattered lol

 

[Deleted member 113831]

I don't do the BC x 10 thing. That is just another rule of thumb. And assumption that a BC of .4 - something will be a 4 gun. Most of the time a decent assumption but no reason to assume. I just true my ballistic computer and then start plugging in wind speeds until the holds/ ranges line up.

My 6SLR shooting DTACs at 3K fps is a 7 gun in the winter and and an 8 gun in the height of high DA summer. So the rule of thumb doesn't work.

Rules of thumb are starting points. They are never meant to be inflexible. Temp and elevation have predictable influences on the rule and can be accounted for without the use of electronics once the general trends are understood.

 

[Deleted member 113831]

True. But in this case, no need. I have a kestral 5700. I only need to find what my base wind is once, every 6 months. I need to use rules of thumbs when I don't have time to consult a kestral. Like during a stage or COF. That's when they're appropriate.

Using the ROT and then going 3 steps to extrapolate the true base base wind when it can be done with more accuracy in less time is just doing it to do it.

It really isn't hard,

200 fps = 1 mph change in base wind.
4000 ft elevation change = 1 mph change in base wind

No Kestrel needed. If you would rather punch buttons, that's your choice to make. Some would rather have the knowledge in their head rather than a device.

 

[blbennett1288]

Good info, thank you for consolidating

 

[ItsChippendale]

Good info, thank you for consolidating

My pleasure, I'll be testing this theory over the weekend at a match more. I wanna prove to myself how accurate it is for my rifle

 

[Quest1000]

I was just playing around with Hornady 4dof yo get my gun mph. It’s a 6.5 Creed. It’s a 6 mph gun. When I adjust the wind angle at 90 degree it gives me .47 hold at 600 yards but when I turn to 270 degree it’s at .6. Why is it giving me a different number at 90 degree? I’m more curious if I have something set up wrong.

 

[Lowlight]

Hornady is adding in drifts

The App used to work, now after an update, the wind is wrong again.

If you go into the sub-menu in Hornady you can get the pure information but it's a sub-menu.

Over the weekend, it was saying a 6.5CM was a 7 MPH Gun, but if you went into the sub-menu it rendered the answer correctly.

The BC in an App is what controls the app's wind calls, so if you understand what the software is doing, you can do it quicker and easier without the flourishes they add-in that corrupt the wind calls.

 

[_Windrider_]

So for the sake updating the "rules" for everyone looking at it, here's what I have so far with some example:

“X mph Gun” Info/Rules

Standard Elevation = 2000ft ASL
Standard Velocity = 2800 fps

For every 200fps increase your mph increase by 1 mph, and vise versa.

For every 4000ft increase in elevation your mph increases by 1 mph, and vise versa

To determine your “base” mph multiply your G1 BC x 10

Example: G1 BC of a 75gr ELD-M = 0.464(Litz) x 10 = 4.64 mph

Now 4.6 mph is correct for 2800 fps @ 2000ft asl. Now for 2950 fps @ 1000 ft asl

Example: 150 fps increase / 200 fps jump per 1 mph = ¾ mph increase

1000 ft decrease / 4000 ft jump per 1 mph = ¼ mph decrease

So adding it all together we get:
4.64 mph + ¾ mph - ¼ mph = 5.14 mph

You then can choose to round to 5 mph for fast and easy numbers.

Now the standard numbers for any giving mph range is

100 yds = 0.1 mil
200 yds = 0.2 mil
300 yds = 0.3 mil
400 yds = 0.4 mil
500 yds = 0.5 mil
600 yds = 0.6 mil
700 yds = 0.7 mil

*past 700yds varies based on calibers, so use real world numbers and ballistic calc to help determine how it lines up past that

So those values on the same bullet from before would be true at 5 mph.

Now for crosswind constants:

Full Value = 1
¾ Value = 0.9
½ Value = 0.7
¼ Value = 0.4

So for another example: if we have a 12 mph, ¼ value wind @ 700 yards

12 mph x 0.4 (¼ wind constant) = 4.8 mph

So you would use your 700 yard 5 mph wind value hold of 0.7 mils.

*(The 0.2 mph will be impossible to account for because wind is a fluid and nobody is capable of shooting a noticeable difference that the 0.2 mph could give in theory so we ignore it)

My only feedback is don’t think in decimals. Round down to the nearest whole number. Keep it simple.

 

[Quest1000]

ok Thanks! That’s what I wanted to know.

 

[SRTWingIt]

I'm somewhat late to this party, but the information has been useful to me and I think I understand how it all works. So, to help me and to make the information easy to find, I made some log book sheets that can be printed off on the rite in rain loose leaf pages so they can be inserted into a log book. I figured I would share it here so if I got something wrong I can fix it and if it would help someone else you can have it. I also Included one I filled out. Please let me know if it's missing anything or needs fixed. Hope it helps.