POI change with altitude change

[LarryBud]

Hello All,

This may not be a true long range question but does anyone know what to expect for POI moment from 1000’ to around 7K’?
When I use the ballistics calculators there minor changes but it assumes I zero at 7K.

I don’t have the opportunity to practice up high and live at 1000’.

The CF guys say it’s negligible but I’m guessing it may be greater at 1400’ per second.

 

[ENCORE50A]

Hello All,

This may not be a true long range question but does anyone know what to expect for POI moment from 1000’ to around 7K’?
When I use the ballistics calculators there minor changes but it assumes I zero at 7K.

I don’t have the opportunity to practice up high and live at 1000’.

The CF guys say it’s negligible but I’m guessing it may be greater at 1400’ per second.

One thing I like about Strelok, is that you can set your zero at a certain altitude, say 1000', then after all the data is completed, you can change the altitude and it will give you the change.
I will admit I haven't used it since using the custom.

 

[LarryBud]

Thanks. I’ll check it out.

 

[ronlaughlin]

Hornady has a calculator on their website. It works good. Here is a calculation of one's hunting bullet done for 1000 feet elevation.

It shows the bullet drops 41½ inches at 300 yards.

Another calculation was done for 7000 feet elevation -- that follows.

Note the same bullet with the same muzzle velocity drops 37½ inches at 300 yard.

Considerable difference, but easy to adjust for. For a 300 yard shot one dials up 13.2 moa at 1000 feet, but only 11.9 moa at 7000 feet.

 

[LarryBud]

Thanks Ron,

I guess what I have in my mind is that the 7000’ calculation assumes a 100 yard zero at 7000’. Yes, the drop is less at elevation but I will zero at 1000 and then move to 7000. Am I over thinking this? Perhaps a 100 yard zero at 1K is about the same as a 100 yard zero at 7K and the above adjustment is all I need to worry about.

I’m looking at buying a Nikon Spoton Turret for my Nikon Omega. I can tell the to set the elevation for whatever I want.

 

[ronlaughlin]

Well Jeff, two things come to mind.

First, on TV shows the outfitter, or hunter always check zero on their rifle when they arrive. You can adjust your zero, probably not at 7000 feet, but perhaps at 4000 feet or some such. Possibly TV is not quite true.....................?

Second, we lived, and hunted Montana for more than 40 year. We sighted our rifles in at about 3500 feet elevation, and hunted anywhere from 5000 feet to 8500 feet. To my knowledge we never missed an elk, because of issues caused by elevation. If we did we ignorant, never used elevation as an excuse for a miss. We thought we missed because we were excited.................

We never had chronographs, they weren't for sale. About the only good tech we had was wool. Dam feet always got wet. Awful thing when wet boots freeze in the night. Slept with a small can of V8 in the sleeping bag so it wouldn't freeze.

Later on we bought chronograph, and paid for ballistic calculator, thus were better prepared. One thing noticed, was the bullets used always seemed to fly better than calculated, when we shot out 300 yard at paper.

The last 15 years of elk hunting found us sleeping in a tent heated by wood, or even a trailer heated with propane. Nothing better than a wood heat. My, that was wonderful. Boots had gore-tex in them. Feet never got wet. GPS kept us from becoming confused. Camp was at 6500 feet elevation; we hunted from there up to 8500 feet elevation. Never sighted the rifles in at camp, did that back down at 3500 feet. Didn't miss much...............

 

[LarryBud]

Thanks Ron,

I’m probably overthinking it.

 

[ronlaughlin]

......probably overthinking it.

No, No, just preparing. Nothing wrong with being prepared. Last week i stumbled into a couple of elk up in the hills when went up to shoot............gets one's heart going, it was fun.

Should be great fun for you; this hunt. Work on your breathing, work on your breathing.....

 

[brucebuilds]

Thanks Ron,

I’m probably overthinking it.

You aren’t necessarily overthinking it, depending on your expected range. At a couple hundred yards there will still be enough difference to be noticeable, but likely not enough to cause a miss. At longer ranges there is a huge difference. I zero my .338 lapua at 500 where we live, elevation 2450. I shoot it at the cabin, elevation 6300. At 1000 yards the impact difference between home and the cabin is 6 feet. These numbers don’t apply to muzzle loaders of course, but your instincts were correct. Elevation can make a huge difference.

 

[sdporter]

How far you planning to shoot? If under 300 yards, I wouldn’t worry about it. Just hold a little low at 200+. 100 yards point and shoot. It was only like 4” difference at 7000’, but that’s at 1900 FPS. Might not hurt to check the numbers at 1400. Probably a great idea actually. The lighter atmosphere does create less drag on the bullet. I never really even thought about that stuff before... Great question!

 

[sdporter]

I missed a dandy mule deer the year I bought my first White (.504 Whitetail) had to be 1991 or thereabouts. He was about 200 yards away, down hill, (no rangefinders those days) I had a good solid rest, put my red dot right on the top of his back, squeezed the trigger, and was surprised to see the bullet hit just high. I had only shot the rifle at out to 200 yards at 2500’ and knew it hit about 16” low. I was hunting at about 4000’. Never practiced a down hill shot before, yep blew that one...

 

[LarryBud]

How far you planning to shoot? If under 300 yards, I wouldn’t worry about it. Just hold a little low at 200+. 100 yards point and shoot. It was only like 4” difference at 7000’, but that’s at 1900 FPS. Might not hurt to check the numbers at 1400. Probably a great idea actually. The lighter atmosphere does create less drag on the bullet. I never really even thought about that stuff before... Great question!

I have an outfitter in MN. I've been told to be proficient to 300 yards. I hope that's just to get me focused on being solid at shorter ranges but I'll be working on it. I'll be hunting in steep country at 6-8 K. The problem is that I live at 1K on the prairie of KS. Plus, Covid has closed all the ranges!!

One step at a time but I suppose I need to think about factoring for shot angle as well.

 

[ronlaughlin]

.........Might not hurt to check the numbers at 1400............

Just need to know an approximate ballistic coefficient. A bullet weight would be helpful.

 

[ENCORE50A]

Hello All,

This may not be a true long range question but does anyone know what to expect for POI moment from 1000’ to around 7K’?
When I use the ballistics calculators there minor changes but it assumes I zero at 7K.

I don’t have the opportunity to practice up high and live at 1000’.

The CF guys say it’s negligible but I’m guessing it may be greater at 1400’ per second.

I'm always curious with questions concerning long range shooting and although this isn't long range, its still interesting. So, I did some searching. Obviously its best to re-zero the rifle when there is a large increase in elevation. However what appears to be an agreement is, if you zero at 100yds at 1,000' above sea level and hunt at 8,000', the change at 8,000' of your original 100yd zero at 1K is extremely slight, from everything I could find. The worst case example identified was 1 click (.250moa) at 100yds.
I suspect you are not planning on actual long range shooting/hunting? If that's true, then the change out to 200yds shouldn't be enough to worry about. Maybe .5moa? If you look over Ron's charts, even assuming that the zero was set at 7K, there's .5moa difference than at 1K.
Interesting stuff. What I did notice when searching, it appeared the highest percentage of shooters, at long range and changes in altitude, used Applied Ballistics. All of the information I could find was with CF though.

 

[LarryBud]

I'm always curious with questions concerning long range shooting and although this isn't long range, its still interesting. So, I did some searching. Obviously its best to re-zero the rifle when there is a large increase in elevation. However what appears to be an agreement is, if you zero at 100yds at 1,000' above sea level and hunt at 8,000', the change at 8,000' of your original 100yd zero at 1K is extremely slight, from everything I could find. The worst case example identified was 1 click (.250moa) at 100yds.
I suspect you are not planning on actual long range shooting/hunting? If that's true, then the change out to 200yds shouldn't be enough to worry about. Maybe .5moa? If you look over Ron's charts, even assuming that the zero was set at 7K, there's .5moa difference than at 1K.
Interesting stuff. What I did notice when searching, it appeared the highest percentage of shooters, at long range and changes in altitude, used Applied Ballistics. All of the information I could find was with CF though.

Thanks doing the research. It appears that of the many things I need to worry about, the alititude change is not one of them.

Now back to the basics of load development. I plan on prepareing two rifles. Currently, it will be a fast twist Disc 45 with a 465 Conical / T7 3F and a Disc .52, 325 FTX and BH 209. Should be at 1400 FPS on the big lead and around 1900 on the FTX. Thats my current plan anyway.

 

[sdporter]

Just need to know an approximate ballistic coefficient. A bullet weight would be helpful.

That would certainly help. I have wasted so much powder and lead shooting at rocks on hillsides at out to 425 yards, but hey, I love to shoot so no big deal.
I don’t own a chronograph so I never know how fast my bullet is going. I Have found, through a lot of trial and error, that on 6X my bdc reticle works pretty good out to about 200-225 yards shooting conicals, with each hash or dot under the center being roughly 50 yards.
I don’t ever mess with the turrets on my muzzleloader scopes, they’re cheap Nikon P Tactical 3X9’s and I don’t trust them to return to zero.
I also have a couple of Vortex Diamondback 4X12’s. They must have a ton of backlash in the adjustment or something weird, because when I initially zeroed them, if I wanted to move the group 2” it either didn’t move, or would go 6”.
I hate buying on a budget.

 

[LarryBud]

I don’t ever mess with the turrets on my muzzleloader scopes, they’re cheap Nikon P Tactical 3X9’s and I don’t trust them to return to zero.
I a

You make a really good point here. I plan on using Nikon Omega’s ( I have 4 ) which were the front runner to the Nikon XR Muzzleloader Scope. They are pretty decent scopes but wont be found on any sniper rifles.

Two of my Omega’s have the BDC built in and the Nikon “ Spoton “ software will get me close. That may be a better way to go. No adjustments once zeroed.

 

[LarryBud]

Just need to know an approximate ballistic coefficient. A bullet weight would be helpful.

The 325grain FTX Is 0.23 per Hornady
The 465grain Lead is estimated to be around .3 I believe.

 

[ronlaughlin]

OK.....................we know the mv is 1400 fps; we know the bullet weight is 465g; we don't know the ballistic coefficient.

Guessing the ballistic coefficient of this bullet to be 0.25 guessing.

 

[Renegadehunter]

I use strelock. It allows you to put in the elevation, barometric pressure and temperature for "sight in". Then when going hunting I can put in the current altitude, barometric pressure, and temp and the drop is calculated accordingly, there is a toggle under zeroing weather labeled "zeroing weather. Enabled" that you have to make sure is "on". I would assume most decent calculators have this ability.
Then it's best to check how accurate it is calculating the drop vs. reality. I set up a couple of my modern rifles without a chrono and just adjusted the velocity in the calculator until the drop it showed matched what I was actually seeing on target.
Even only shooting at 1000', if you get the calculator matching your actual results on target you then should be fine to move to 7000' and input the new altitude and weather data into your calculator. You could even check it when you get to hunting camp, simply put in the new altitude and weather data, see where it says you'll hit at 100 yards, and then shoot and see if it is correct.