FPS and MOA calculation

[Chiquita]

Is there a formula or a way to figure out the following:

Say the the speed of the projectile changes by 20FPS, how can I find out what elevation effect that will have at 1K range?

Thanks

 

[Charlie-NY]

Simple - use any of the on-line ballistic calculators.

 

[caihlen]

Strelok.

 

[338 dude]

I use Shooter or Applied Ballistics, LLC

 

[Chiquita]

Any formula besides the app?

I do have the strelok app.

 

[Lone Hunter]

Any formula besides the app?

I do have the strelok app.

Do you have Strelok Pro or the regular Strelok? I have the Pro version (I am not a Pro, just an idiot) and like it very much. You can see what your come up is at a certain range and it will tell you what your muzzle velocity is. I don’t know of a formula but am sure there is one. Too easy to put my come up in and let the computer do it. I’m lazy too..

 

[Forum Boss]

Go online for free JBM Ballistics. The basic version (Trejectory Simplified) is a little easier to use:

JBM - Calculations - Trajectory (Simplified)

www.jbmballistics.com

 

[Dgd6mm]

Shooters App

 

[Ned Ludd]

Is there a formula or a way to figure out the following:

Say the the speed of the projectile changes by 20FPS, how can I find out what elevation effect that will have at 1K range?

Thanks

As Forum Boss noted, JBM is a very good ballistics program available free online. Just be aware that you need to set the zero range at some specified distance, let's say 100 yd, then compare the predicted drop at two different velocities in terms of inches/MOA at 1000 yd. The difference will be due to the change in velocity. There may ways to do the same thing at JBM without setting a shorter zero distance, but I've never done it that way. I've used the JBM Trajectory (Simplified) calculator many times to estimate the difference in elevation caused by a change in velocity at some specified distance and it's close enough to actual that any difference there may be isn't worth talking about.

Below are two readouts from JBM for a .308 Win load with the Berger 200.20X bullet loaded at 2630 fps, and 2650 fps. From the difference between the two drop numbers at 1000 yd, the 20 fps difference in velocity would be worth ~5.7", or 0.6 MOA, on the target.

 

[Curmudgeon]

How do you know all your bullets leave and arrive at the same speed? What is your spread? Seems like you should figure from mean velocity. How is SD influencing spread?

 

[Chiquita]

I do have the strelok pro and I will look at the mentioned site and see if I can figure it out.

May be it was not a valid question after all.

 

[Chiquita]

How do you know all your bullets leave and arrive at the same speed? What is your spread? Seems like you should figure from mean velocity. How is SD influencing spread?

I don't know that all the bullets are leaving at the same speed, hence my question If there is a 20FPS difference between the speeds by what distance will I miss the target by at 1000 yards? 15 feet, 46feet, 25' feet?
Assuming everything else stays the same.

I guess I can go inot the programs and adjust the speed and see on the chart. But I was thinking there was a formula that I use. I am sure there is because shooting, ballistics and math have been around a lot longer than the shooting apps.

 

[Chiquita]

I think I got this.

OK, in my Strelok app once I adjust the speed by 20FPS the absolute drop changes by 6.5". I assume that means that my POI will change by 6.5".

 

[Capt. Oblivious]

I think I got this.

OK, in my Strelok app once I adjust the speed by 20FPS the absolute drop changes by 6.5". I assume that means that my POI will change by 6.5".

Yet in practice it doesn't really work like that otherwise no one would be able to hit anything at 1k unless they had a 0 ES spread

 

[Dgd6mm]

Yet in practice it doesn't really work like that otherwise no one would be able to hit anything at 1k unless they had a 0 ES spread

Yeah, then you have to shoot the conditions correct also. This plays a very big part.