Ballistic Calcs. - A little help

RobSky · Sep 13, 2018

If someone could help me out, I would appreciate it.
Going hunting out West next month, and can only sight in at 100 yard range.
May need to go out a little further for the hunt.

I'm running the following:
7mm rem mag 24" barrel standard rifle
160 gr TSX BT
2950 muzzle velocity
Coef - .443
Sighted in at 2 1/2" high at 100 yards
Avg elev 8000 ft
Avg temp 40 degrees
Looking for 200, 300, 400 ,500 yard calcs. to tape to my gun.

If you could post or PM the info, thanks.

E.Shell · Sep 13, 2018

You can do this yourself online at http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

You will learn a lot playing with it.

Use your 2.5" high at 100 in the "Zero Height" input field.
Your caliber is .284.
Your sight height is probably close to the 1.5" default if it's a standard hunting rig.

I would set the range increment to 50 yards (or even 25) because the bullet will start to drop more rapidly at longer ranges and 100 yard increments will leave you with a lot of big gaps and guesswork. At 2-1/2" high at 100, you probably have about a 250 yard zero. You can use 200, 250, 300, 350, 400, 425, 450, 475 and 500 yard numbers for your rifle card, for example.

Use default for most other fields, except your environmentals. You'll want to plug in your 40oF and your 8,000', but you can leave the pressure at its ICAO standard value. Humidity does not matter, but you can plug in 78% if you want to used standard conditions. Once you get useful output numbers, you can experiment with humidity numbers if you doubt it doesn't matter at 500 yards.

Select inches if you are used to thinking that way. If you plan to dial your distance or hold it using mildots, etc., you can select mils or moa down at the bottom left area.

Your basic 100 yard zero will NOT be affected by your altitude change from MD to 8,000 feet, but you will risk zero change from transport handling.

If you have difficulty, let us know.

RobSky · Sep 13, 2018

Thanks Ed!

danb · Sep 13, 2018

if you have a smart phone, download "Strelok"

OLM-Medic · Sep 13, 2018

Ed is spot on.

The only thing I will add is that this ballistic chart may not be true to your gun. I've found that you need to actually go to the range to true the chart, and make corrections. I imagine if you had a chronograph to know the exact velocity, this would be less of an issue.

Pinecone · Sep 13, 2018

I use Ballistic AE on my smartphone. It uses the same calculation engine as JBM does.

Bountied · Sep 13, 2018

OLM-Medic said:
Ed is spot on.

The only thing I will add is that this ballistic chart may not be true to your gun. I've found that you need to actually go to the range to true the chart, and make corrections. I imagine if you had a chronograph to know the exact velocity, this would be less of an issue.

This, there is no substitute for actual DOPE. Most of the time the calculators will get you close but not 100%. If you miscalculate anything the calculator will factor it in and your holds will be off. I had a rifle with a 200yd zero, I went to shoot 500yds using my data in the istrelok app and I was a good 2' low at 500. Maybe my velocity was off, scope height wrong, pressure, temp etc.

Delmarva sporting clays has ranges at 100, 200, 300, and out to 500yds. I wouldn't try a shot on live game past that if I didn't have a solid DOPE.

OLM-Medic · Sep 13, 2018

Bountied said:
This, there is no substitute for actual DOPE. Most of the time the calculators will get you close but not 100%. If you miscalculate anything the calculator will factor it in and your holds will be off. I had a rifle with a 200yd zero, I went to shoot 500yds using my data in the istrelok app and I was a good 2' low at 500. Maybe my velocity was off, scope height wrong, pressure, temp etc.

Delmarva sporting clays has ranges at 100, 200, 300, and out to 500yds. I wouldn't try a shot on live game past that if I didn't have a solid DOPE.

I would imagine having exact FPS measurements with a chrono would help.

Even then, I've switched lot numbers of the same ammo and missed by a foot at 600y before. Of course this was with .223. The better long range cartridge you have, the more these effects will be minimized, but still exist. Temperature and elevation shouldn't matter too much at 600y and under.

On the other hand, I think powder temperature, as opposed to actual ambient air temperature, can screw with your velocity too. If it's cold as hell the powder may burn slower, thus less velocity, thus not accurate drop charts. I'm still a noob, but that's what I understand.

DaemonAssassin · Sep 13, 2018

Hornady has a ballistic calculator you can download for your phone/tablet.

antco · Sep 13, 2018

Good thread.
I use a phone app called Shooter, and judge my rifles personalities from there.

Ballistic Calcs. - A little help

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