Weather Conditions Affecting 0 ??? Please help.

[footman2000]

I would love some advice. I have a custom rifle I use in f-class competitions and practical rifle matches. I will have the gun 0'ed at 600yds then the next time I go out to a match I will have to re 0 1-2 MOA vertically. Once I reestablish 0 it punches tight groups and holds 0. Is this normal with a change in the weather conditions? Temps do vary.

I am shooting a Krieger barrel fully floated chambered in 6.5 Creedmoor, Surgeon action, on a Bell and Carlson Medalist Varmint/tactical stock. My Scope is a 10-50 x 60 Sightron with leupold rings. Everything is tight and secure as far as I can tell. Ammo shows very consistant velocities at 2830fps. I would love any advice you may have.

Thanks in advance,
Terry

 

[bigwheeler]

Re: Weather Conditions Affecting 0 ??? Please help.

Weather always affects a shot at 600 yards. Why do you think it's just in the rifle?

 

[billyburl2]

Re: Weather Conditions Affecting 0 ??? Please help.

Run the different temps through JBM, it will show the difference. The problem you are having is due to density altitude. This why I zero at 100 vs. further out.

 

[footman2000]

Re: Weather Conditions Affecting 0 ??? Please help.

I am not sure that it is in the rifle. I just want some reassurance that it is not. It is difficult when we shoot the practical matches at the Whittington Center. Targets are small and if you start off at the wrong 0, the day quickly becomes frustrating. We can test before the match, but we are shooting steel gongs and have no way to check actual impact sites.

 

[footman2000]

Re: Weather Conditions Affecting 0 ??? Please help.

It is not that I 0 at 600yds I just have a 0 with dope at 600yds. This is where I really start to see the variation of my impact sites.

 

[Lowlight]

Re: Weather Conditions Affecting 0 ??? Please help.

The answer is pretty clear, if you suspect a problem with the rifle you have to test it where the external conditions have a greatly reduced effect, like 100 yards. If it can't hold a zero at 100 it won't hold it anywhere else.

Weather conditions will change your point of impact you cannot get around this and is why most "target" competitions allow for sighters as opposed to ones that are more based in field shooting / tactical applications. For this you have to learn how your specific rifle / load combination is effected by changes in weather, such as barometric pressure differences and temperature.

Saying you shot your rifle last month at 600 yards and this week it was off, is one of those "D'uh" moments, of course it will be different, the conditions have changed. DOPE Is often defined as Data on Previous Engagement -- the key word here is "previous" -- it changes, and your data at distances beyond 300m which are visibly effected by weather are a dynamic number, not one to be set in stone in your mind, or anywhere else.

You need to learn and understand the effects of weather on your load, this helps you adjust for changes so you can be closer to center when engaging targets from week to week.

 

[gstaylorg]

Re: Weather Conditions Affecting 0 ??? Please help.

To what has been stated, I would also ask whether the competitions are all at the same location (ie. altitude)? If you are changing altitude for competitions at different locations it can affect your POI in addition to effects of changing atmospheric conditions.

 

[XTR]

Re: Weather Conditions Affecting 0 ??? Please help.

<span style="text-decoration: underline">Density Altitude</span>, you should learn about it. It has nothing to do with the altitude of the dirt on which you are standing.

I have seen my 1000 yd elevation can change by as much as a full MOA between the first relay in the AM and the last in the afternoon.

 

[footman2000]

Re: Weather Conditions Affecting 0 ??? Please help.

Thanks for the all of the information and opinions. First It does hold 0 There is no wandering at all to address Billy as stated in the initial post. After running numbers through JBM ballistic calculator with various atmospheric conditions realistic to colorado rifle club where I shoot regularl at 600 yds JBM has a maximum variance of 2 inches. Is there some other magical condition that is not accounted for? I have run several numbers over the past. It just does not make sense to what I am seeing. I really am not to concered with my rifle, just want to know if there is some explanation for what I am seeing atmospherically that ballistic calculators are not taking into consideration. I want to be able to increase my predictions of a long range 0. I understand, if there is not any atomospheric explanation then that would rule out one possible explanation and point to the rifle.

 

[Lowlight]

Re: Weather Conditions Affecting 0 ??? Please help.

I shot/shoot CRC in Byers and I have seen weather differences of more than 2" at 600 yards so you may not be understanding and inputing the differences correctly.

That said the single greatest effect on the bullet is the shooter, so you might want to look internally at your technique, cheek weld with more clothes on, position, etc. It's up to you to realize that an very few people can diagnose their own shooting, so I suspect if you were the cause it will continue.

You could have a scope problem, I would ask if you calibrated and tested the tracking on your scope but I suspect that is no as well, so you might want to check it across 100% of your useable adjustment range, that would be the most likely culprit beyond the rifle itself and you.

Good luck with your hunt, believe me consistency doesn't happen by accident and if it was easy everyone would be doing it.

 

[tnichols]

Re: Weather Conditions Affecting 0 ??? Please help.

I'm fortunate to be able to have a target at 658 yards from my deck for 5 months out of the year. It is a full size AR400 IPSC target that I get tired of lugging to and from the "range" (a soybean field). I don't take a shot at it everyday, but I usually run the numbers for it through ExBal just for shits and grins. Iowa can have 40-50 degree temp swings from one day to the next, and howling winds as well. It's interesting see how the numbers can change from one day to the next or even morning (30 degrees F) to late afternoon (65 degrees F) as another poster noted. I encourage you to do the same. When you get a free moment during the day, pull the weather from Weather Channel or your local airport and plug it in for a 600 yard shot, and note how it changes from day to day, and I'll think you'll find why your are seeing a shift from one event to the next.

 

[footman2000]

Re: Weather Conditions Affecting 0 ??? Please help.

Billy and XTR thanks for the info on Density Altitude. I originally thought it was a typo because I had never heard of it before. You guys rock and that is why I come to the pros for advice.

Thanks again

 

[diego-ted]

Re: Weather Conditions Affecting 0 ??? Please help.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I shot/shoot CRC in Byers and I have seen weather differences of more than 2" at 600 yards so you may not be understanding and inputing the differences correctly.

That said the single greatest effect on the bullet is the shooter, so you might want to look internally at your technique, cheek weld with more clothes on, position, etc. It's up to you to realize that an very few people can diagnose their own shooting, so I suspect if you were the cause it will continue.

You could have a scope problem, I would ask if you calibrated and tested the tracking on your scope but I suspect that is no as well, so you might want to check it across 100% of your useable adjustment range, that would be the most likely culprit beyond the rifle itself and you.

Good luck with your hunt, believe me consistency doesn't happen by accident and if it was easy everyone would be doing it. </div></div>
Lowlight, does the changes in DA affect pressure as well? I am taking it does. I had a load worked up for my 338 that was pretty stiff. I made up around 40 rounds and shot 30 with no problems. Then on a cooler day by maybe 20 degrees I started getting a sticky bolt, then a stuck bolt. I have since brought down the charge because I do not want that kind of pressure. I was confused why the first 30 rounds were fine?

Diego

 

[LawnMM]

Re: Weather Conditions Affecting 0 ??? Please help.

Yes, weather conditions affect the pressure of your load.

 

[XTR]

Re: Weather Conditions Affecting 0 ??? Please help.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LawnMM</div><div class="ubbcode-body">Yes, weather conditions affect the pressure of your load. </div></div>

Usually the weather effect on the load is temperature. We're not talking about external ballistics here. The usual problem is that a load that to some extent almost all powders burn faster at higher temperature, resulting in higher pressure, so a load that is at the edge at 55 or 75 degrees is too hot at 90F

The poster above who is getting sticky bolt in cooler conditions sounds like there is something missing from the puzzle.

 

[Pat Harrison]

Re: Weather Conditions Affecting 0 ??? Please help.

Not nessessarily. The powder can be inverse sensitive, some powders do get hotter as the temp goes down. One example is IMR 4756 which I use in my pistol. 8.5 grains behind a 125gr bullet will get me just under 1400fps (.38 Super Open gun) in the summer, 30C, but when it's -10C that same load will be pushing 1500fps.

 

[McCrazy]

Re: Weather Conditions Affecting 0 ??? Please help.

LL, the OP is seeing 1-2 moa difference at 600, not 1-2 inches. It is a more significant change but I am sure we all agree that environmental changes can still cause it.

Would be helpful if the OP could tell us from his data what the conditions were and where the rifle was hitting. Then we could see if the weather theory jives or if something else is amiss.

This thread should probably be in one of the marksmanship or exterior ballistics sub-forums.

 

[footman2000]

Re: Weather Conditions Affecting 0 ??? Please help.

The differences I have noticed are usually 6-8 inches high. I made the cardinal sin of not accurately documenting the conditions but I did not have the kestrel 4000 either. I did go back and glassbed the front lug very snug. I have not had a chance to get back out and check to see if it follows my ballistic chart better.