Temperature affect on POI

[nmarchr]

I have a couple questions before my upcoming Colorado deer hunt. I live at 6500 feet, and will be hunting deer between 7K and 9K feet this year. I got a new gun this summer and have spent a lot of time shooting all year. I took it to the range this past weekend to verify everything was still dialed in and ready to go. I set up at 500 and used my app and boom, dead on at 500 yards. This is where i start overthinking things. It was 75 degrees where I was shooting this weekend. During my hunt temps will more than likely be in the 20's and 30's or colder. When I plug those numbers into my app I notice that my bullet drops a lot faster. that same dope at 500 yards could end up in a clean miss for me. Do you all make different dope cards for the conditions you will likely be hunting in, or am I overthinking this process? Would really like to hear what some of you more experienced rifle hunters do in these types of circumstances. I am an archer that does not gun hunt a whole lot. any help is greatly appreciated.

 

[PNWGATOR]

Confirm zero. Trajectory validate and update my app (Shooter).

I then use Density Altitude as the only input to Shooter for new solutions.

It’s that simple.

 

[Nbowlin]

If you have a chrono you could ice a few rounds and get a pretty good idea of what your cold velocity is going to be. Or reverse the process and use the difference in drop to get a new fps.

 

[seand]

For 500 yards I’d just print a dope card for your new average elevation and expected temp. Check it at the min elevation/coldest expected temp and highest elevation and max expected temp to see what the difference is to reassure yourself if the difference is small enough to not worry about for 500 yards

 

[ResearchinStuff]

If you have a chrono you could ice a few rounds and get a pretty good idea of what your cold velocity is going to be. Or reverse the process and use the difference in drop to get a new fps.

Velocity change isn't the big problem. Thicker, cold air resisting the movement of the bullet is the big problem.

 

[hiker270]

At normal hunting distance's say 0-500 yards large temperature changes are not significant.

 

[JF_Idaho]

Velocity change isn't the big problem. Thicker, cold air resisting the movement of the bullet is the big problem.

I think it's actually the opposite. Somewhere around 1-2 fps lost per 20° of air temperature lost, vs 10-20% muzzle velocity loss/gain from 0°-100° with a more temp stable powder being towards the lower end.

 

[TaperPin]

Lower temps reduce velocity out the barrel - at 500 yards it’s not a big deal, but some loads change elevation a great deal due to barrel harmonics right before or after a node far further than what the velocity causes - that depends on your rifle. I wouldn’t lose sleep over it.

Understanding air density is always a plus - the lower temps are one thing and the increase in altitude is another in the opposite direction. At 500 yards it’s not going to be a huge issue.

 

[ResearchinStuff]

I think it's actually the opposite. Somewhere around 1-2 fps lost per 20° of air temperature lost, vs 10-20% muzzle velocity loss/gain from 0°-100° with a more temp stable powder being towards the lower end.

By all means, use a reputable ballistics solver and prove your point.

 

[Reburn]

By all means, use a reputable ballistics solver and prove your point.

How long are we supposed to wait for it?

 

[JF_Idaho]

 

[JF_Idaho]

 

[JF_Idaho]

Hard to edit that together. The first 2 represent 100° change in powder temp, the 2nd 2 a 100° change in weather.

The weather accounts for .4 moa
The powder temp accounts for 2.9 moa

Both at 500 yards

 

[ResearchinStuff]

So what powder has a 2.5 fps per degree temp sensitivity like you've shown? H4350 is about .2, it is among the most temp stable. TAC, a double base spherical powder, ie temp sensitive, is 0.82 fps per degree. Your velocity change of 250 fps for 100F strikes me as competed unrealistic.

 

[JF_Idaho]

Well to answer your specific question, that's the sensitivity factor that strelok added when I selected the cartridge.

But, even if we go to the sensitivity you listed of H4835, I'm still right, correct?

So after moving the goal posts, how about you show me on a ballistic calculator how I was wrong?

I mean your assertation was that powder temp has no effect....and regardless, the effect air temperature has on trajectory is minor, contrary to what you said.

 

[JF_Idaho]

And upon further research the fps drop per degrees for powders are measured from 33° to 100° , so I am guessing that there is a more drastic change from 33° to 0°. Although, that is an assumption.

 

[ResearchinStuff]

The goalposts haven't moved. You showed a velocity change that doesnt match any powder in existence, and it is because you have your solver set up improperly using a default value that is nonsensical.

My h4350 load, with the correct .2 fps per degree correction factor:
5000 ft da, 0F


5000 ft da, 100F


500 ft DA, 100F


500 ft DA, 0F


At 500 yards, changing the temperature causes about a 10 fps difference in retained velocity. Changing density altitude by 4500 ft causes a retained velocity change of about 90 fps. Solutions for 500 yards, 0F and 100F differ by 1 click or less at the same DA. Solutions for 500 yards at the same temperature, but 4500 ft different DA differ by 1-2 clicks.

 

[Reburn]

Well to answer your specific question, that's the sensitivity factor that strelok added when I selected the cartridge.

But, even if we go to the sensitivity you listed of H4835, I'm still right, correct?

So after moving the goal posts, how about you show me on a ballistic calculator how I was wrong?

I mean your assertation was that powder temp has no effect....and regardless, the effect air temperature has on trajectory is minor, contrary to what you said.

Do yourself a favor and un check the box consider powder tempature in strelok.

Also do yourself a favor and always speak in DA. Density Altitude. Its the only metric that matters.

 

[TaperPin]

Density altitude is easier to visualize in a graph.

Adiabatic lapse rates vary, but are often listed as an average. On a clear dry day it’s over 5 degrees per 1000’

 

[JF_Idaho]

I can't really uncheck consider powder temperature, when I am literally considering the powder temperature.

I'm not understanding how density altitude translates to this conversation specifically.

0° @ 1000ft is more dense than 0° @ 2400ft correct?

So in this specific instance we are taking a 100° swing at a specific altitude. I understand that could be interpreted to different numbers at different density altitudes (correct?) Just don't see how that is relevant to this topic.

But, I will try to learn more about it. If there's something I'm missing, please explain.

While H4350 may translate that way, as you even said it is one of the most temp stable powders. The exception, not the rule. I know Alliant Reloder powders are very temp sensitive.