Elevation effects on bullet trajectory

[oldmossy]

One thing for sure..you can bet I will be chronoing my rifle every chance I get from 10 degrees to 100 degrees. Logging environmental data. And actual drop data. I will do my best to know where Im gonna impact on any given day.

 

[LRNut]

When I shoot LR, I set up my LabRadar next to my rifle; I do the same when testing/working loads at 500 yards (my preferred range for testing LR loads). I generally keep a logbook of the range, the conditions, how I called the wind, what I held for wind, the results, MV, and where I hit. I shoot constantly and it is not unusual for me to notice slight movements in my zero due to different bullets, powder, etc.

 

[Mikecr]

A common issue with ballistic software, IMO, is actually a dismissal of Rh%.
For example, many do not adjust Mach# with Rh. This throws errors into their results, as the software looks up drag numbers per mach#.
This is often accompanied by 'it's not much'.
But it's really 'not much here' and 'not much there', adding, as they also dismiss it in their form factor calcs everywhere throughout the process.

We might observe humidity not mattering much, because humidity changes are typically less than temp and pressure, and it is a smaller affect to air density.
But here where I live(coastline), humidity is just always high. NEVER low summer or winter.
Where/when I hunt(mountains), it's always low, NEVER high.
I get to see it, my modified software fully accounts for it, and I need it to.

It's a smaller thing, similar to coriolis, spin drift, slope, level, resting firmness, mirage, etc.
But I think shooters who work to hit at distance with single cold bore shots, do not dismiss them, or their summation.
Temperature matters too. Powder merchandising does not get you out of barrel & bedding temps.
And pressure matters enough that you need to disregard every altitude shortcut and flat out measure & account for absolute pressure.
Each is easy to consider, so we can do so.

 

[Sako1756]

I've noticed the actual direction of sighting ones rifle in, whether it be shooting north, south, east, or west at 100 yard or 200 yard zero and going into a different elevation with a different shooting direction from sight in can change your POI after 5-600+ yards sometimes close to a MOA. I think wind will be your hardest factor and of course if you sighted in on a bench with a tripod or sighted in laying prone with a tripod! Hell, even laying down with a tripod in prone while hunting and shooting 500 plus will have a different poi compared to a controlled sight in zero from a bench.

 

[oldmossy]

Temperature and barometric psi will be with me at all times from now on. Just ordered this GGB 100 G-Shock watch

 

[oldmossy]

I have a question. Is it possible to mount your scope a little canted to compensate for spin drift? And since we on scope mounting. If your crosshairs is plumb to your level, does it matter if the scope isnt mounted perfectly level on the rifle?

 

[Mikecr]

I have a question. Is it possible to mount your scope a little canted to compensate for spin drift? And since we on scope mounting. If your crosshairs is plumb to your level, does it matter if the scope isnt mounted perfectly level on the rifle?

Yes on spin drift.
PLUMB should always be w/resp to elevation(hold off or dialed) you're actually shooting(POI) at distance.
The rest, rifle, bases, rings, scope turrets, and reticle itself(if dialing) do not really matter.

 

[oldmossy]

So I chronoed my rifle after work this morning @ 20 degrees. 2962/2970. My original testing months ago @ 60 degrees was 2932/2948. Not sure how accurate chrono is. But that's what I got. Anyways...
Took a nap, then went to the range. Now its 34 degrees. Chronoed and shot @ 200yds. Speeds about the same. Fired 2 rounds, which cut holes, But 2" low at 200. Bingo! Theres why my gun was shooting low at 615 last time I thought. Doesn't make up for 1.5 moa, but theres 1 moa of it accounted for. Went from 200 to exactly 600. Shot 3- 2 shot groups with adequate cooling between rounds/groups. All 1/2 moa groups. But 1 moa higher than it should be. Scratching my head, I went back to 200 to check my zero again. Fired 2 shots. 1/2" group. But 2 moa high.

So as much as I hate its the scope. Im relieved I found the problem. In this process though, I gained a little more knowledge by researching powder sensativities, rate of twists, and barometric psi effects. So wasn't a total loss. Plus I got a cool watch outta the deal.

So to the original poster. Maybe my Rangefinders aren't as bad as I was thinking after all. I be sure to let you know with further testing. I have my notes for cold weather. Just need some warmer days to see results

 

[Hugnot]

I try to stick a target on a cardboard box having a rock inside it and laser measure back 300 yards or more & verify zero - provided this can be done in general location of hunting area (I like that fouling shot). There are many other variables such as barometric pressure, humidity, & temperature that need to be considered but most often a 300 yard plus verification will help. After traveling 1,000's of miles best to not screw things up. Note that some ballistic programs require elevation input others barometric pressure but all of them appear to require temperature. Should it be wet, cool,& windy at 5000 feet plus and then if a high cold front moves in, the situation would change - this happens.

 

[LRNut]

I try to stick a target on a cardboard box having a rock inside it and laser measure back 300 yards or more & verify zero - provided this can be done in general location of hunting area. There are many other variables such as barometric pressure, humidity, & temperature that need to be considered but most often a 300 yard plus verification will help. After traveling 1,000's of miles best to not screw things up. Note that some ballistic programs require elevation input others barometric pressure but all of them appear to require temperature.


View attachment 257247.

I would just range a bare rock 500 yards or so and check my zero that way. I am sure some don't want to make noise, but I am astounded at how unfazed the deer are on my CO prop - I haven't actually watched what they do when I am shooting, but I see them feeding quite often right after a shot. Even in Arizona a bedded deer will not necessarily bolt just because I zing a bullet over their head - I have kicked them up after shooting walking to my target.

The other issue is a change in zero from dings and knocks. For that, I shoot a target at 100 yards at home and bring that for my hunt.

 

[Mikecr]

Deer are exactly as dumb as cows..
On a farmer's beer-bet I dropped a doe with a brain shot from a little over 500. Two others, right next to it, looked up as the shot echoed all over, and then back to grazing.. I could have dropped them all right there, but chose instead to hit them & more on Pennsylvania highways.

 

[LRNut]

Ok shot yesterday in Arizona for the first time since shooting in CO last Saturday. I had been hammering my gongs at 715 and 905 at my CO place, which is at 8750 feet. Took out two of the rifles I shot in CO.

Shot at 790 yards with one of my 28N's; mirage was pretty fast and flat at first; originally figured 10 mph, but when I focused on it using my parallax knob, it just didn't see like a 2.25 MOA wind hold, so I held 1.5. SIG said drop would be 13.5 MOA IIRC; in any event, I hit my 2.5" aiming circle dead center.

Got out my Lapua and shot at 1180 yards, which was about 45 deg from my 790 target. SIG said come up 29. By now the wind was all over the place; first glance I figured 4-5 MOA. Then it dropped and I figured it was 6mph from effectively 9, so I was going to hold 3 MOA. But then it died, soon to be blowing from the right. I was getting antsy, but wanted to wait for it to settle down. I hate shooting in temporarily calm conditions, but I fired with a slight mirage to the left. Figured spin at 1180 would cancel out any drift. Hit just off the circle.

Bottom line: The SIG adjusts for barometric pressure/altitude pretty well.

 

[oldmossy]

Ok shot yesterday in Arizona for the first time since shooting in CO last Saturday. I had been hammering my gongs at 715 and 905 at my CO place, which is at 8750 feet. Took out two of the rifles I shot in CO.

Shot at 790 yards with one of my 28N's; mirage was pretty fast and flat at first; originally figured 10 mph, but when I focused on it using my parallax knob, it just didn't see like a 2.25 MOA wind hold, so I held 1.5. SIG said drop would be 13.5 MOA IIRC; in any event, I hit my 2.5" aiming circle dead center.

Got out my Lapua and shot at 1180 yards, which was about 45 deg from my 790 target. SIG said come up 29. By now the wind was all over the place; first glance I figured 4-5 MOA. Then it dropped and I figured it was 6mph from effectively 9, so I was going to hold 3 MOA. But then it died, soon to be blowing from the right. I was getting antsy, but wanted to wait for it to settle down. I hate shooting in temporarily calm conditions, but I fired with a slight mirage to the left. Figured spin at 1180 would cancel out any drift. Hit just off the circle.

Bottom line: The SIG adjusts for barometric pressure/altitude pretty well.

I like it

 

[WYODAN]

That's good news I really want to buy one because of size and everything I have investigated on them.