Advanced Marksmanship Chasing the WX

[rickp]

This past weekend at a shooting event i found myself chasing the weather. So i have 2 questions about it.
How much should temp change before one recomputs their dope? I loomed at some numbers in FTE and came up with 10deg when shooting past 400/500 yards. At that amount and distance the dope changes enough to affect when one rounds up or down 1/10 of a mil. And when shootin small targets it could make a difference.

My second question is is along the same lines: after you build your dope card upto what temp/ humidity/PA is that still good for?

 

[BOLTRIPPER]

Re: Chasing the WX

dtac cards and a kestrel, or a kestrel and some ballistic calculator that gins up DA/dope solutions.

 

[rickp]

Re: Chasing the WX

Im not sure what your saying here or how much wx change before having to recompute.

 

[DCR]

Re: Chasing the WX

He's telling you what to use to find your answer. Density Altitude (DA) and the tools to find it. Kestral and balistic program or DA card etc.

 

[BOLTRIPPER]

Re: Chasing the WX

savvy the guy from CT..................

 

[Lowlight]

Re: Chasing the WX

There is no "one answer" it depends on how temperature sensitive your bullets are to determine how much of an effect the weather will have. Usually 10 degrees is not gonna make that much difference, however if your system is sensitive to 10 degrees you have to account for it.

There is no substitute for going out and shooting it, and you'd be surprise how much is more you than all these other factors you are currently chasing.

Anecdotally, shooting the local matches here in CO on very small targets out to 550 yards, the weather didn't have any effect until 4 - 5 hours into the match, the last relay. Before then, there was no effect, I saw a 1/10th change when the temp went from 65 to almost 90 degrees, even then, it was small, 1/10th just to center up though not necessarily a miss. It was more me getting fatigued being on the line from 10AM to 2-3PM that did it.

I know you are looking for answers to what you consider a bad performance during the match, but I would suspect the answer is between your ears, not the rifle, not the ammo, not the weather.

 

[Lowlight]

Re: Chasing the WX

As a follow up,

Based on the results what were the sizes of the missed targets and were they all an issue of elevation ?

Also were they UKD and based on that was it simply a bad call ?

Provide some after action details to help determine if the powder was indeed temperature sensitive to within 10 degrees, or something else ?

 

[rickp]

Re: Chasing the WX

I agree, I think the issue is all me. I'm just trying to answer some other questions of thing that I did during the event, for example chasing the temp and updating FTE (WAY TOO AFTEN), so I don't do it next time.

I didn't know if there was a "wx change standard" for updating FTE or anyother form of dope.

I ran some arbitrary numbers today and with a 10 deg change the difference was negligible.

So how would one determine if the ammo is temp. sensitive when out shooting?

 

[CoryT]

Re: Chasing the WX

The best way to sus out temp issues is with a chronograp, a freezer, hand warmers and some range time. Freeze some ammo overnight, then pack it in cold packs in the cooler. Leave some at ambient and wrap some more in heat packs. Use some temp probes or thermometers to check the temp of the rounds, then shoot them over the chrono and record the velocities. Plot them on a graph along with the temps, it's normally quite linear.

Now plug the velocity ranges into the computer for the max range and mid range and see what effect it would have. When you see 2/10 of a mil shift, you need to update, under that there's a certain amount of shooter hold error anyway, so don't obsess.

If the targets are under 1/2 MOA in size, you are talking a pretty low percentage shot, UKD, field conditions, so +/- .1 mil dones not really amount to much.