MOA changed-conditions or equipment?

[silver star]

Last summer I attended precision rifle training in which I was able to create very good dope for my setup.
JP CTR02, 18” barrel, shooting Hornady Match 75grain.
Dope is/was spot on for 100, 200, 300, 400, 500 & 600 yds.
Summer time, 100 degrees, gun clean, wind <5mph.

This past Sunday I attended a match on the Hi Power range at OKCGC.
Shot 200, 300 & 600 using dope from past summer.
Winter time, but 40 to 50 degrees, wind <18 from left rear 1/4, gun dirty from 3gun match day before.
No problem at 200. Shot low at 300 and while I thought it strange I just adjusted and shot.
However at 600 I was 18” low or 3 MOA at that range.
My question,
Can climate have that much affect?
If so I would guess that I need to make notes in my dope book.
OR:
With heavy use on gun and optics, >4k rounds, in that period of time should I ignore climate change and adjust MOA due to use and abuse?

Scope, Trijicon, TR-24-3G

 

[Wall]

was it the same ammo?

 

[TroyF]

The first place i would look is at the ammo as well. Same brands doesnt mean a whole lot, ive seen variance in lot numbers of the same brand.

Each time I change from one lot number to the next, I have to check my dope.

 

[Wall]

Each time I change from one lot number to the next, I have to check my dope.

Troy checking his dope

 

[Matt1911]

Is this the free crack giveaway?

 

[silver star]

I bought a case lot back in the summer in order to have extra after zero established.
This ammo is from that same case.

 

[Wall]

Then I would blame conditions. The scope is quality as is the rifle.

 

[brandt9913]

Some rifle powders can be very temperature dependent. When shooting 600 yds, you can throw off elevation 2-3 MOA just by leaving a round chambered in a hot rifle for more than 5-7 secs. Same goes for the ambient temperature being 30-50 degrees cooler. When I was reloading with RE-15 for matches shot in summer months, I would have to adjust 2-3 MOA at matches in the afternoon versus strings shot at 900am before it got hot.

I planned to switch to Varget because they claim it is less temperature dependent, but I discovered action pistol and 3 gun. I haven't shot a 600 yard match since then.

 

[silver star]

Some rifle powders can be very temperature dependent. When shooting 600 yds, you can throw off elevation 2-3 MOA just by leaving a round chambered in a hot rifle for more than 5-7 secs. Same goes for the ambient temperature being 30-50 degrees cooler. When I was reloading with RE-15 for matches shot in summer months, I would have to adjust 2-3 MOA at matches in the afternoon versus strings shot at 900am before it got hot.

I planned to switch to Varget because they claim it is less temperature dependent, but I discovered action pistol and 3 gun. I haven't shot a 600 yard match since then.

Wow! That fits my situation.

 

[TroyF]

Some rifle powders can be very temperature dependent. When shooting 600 yds, you can throw off elevation 2-3 MOA just by leaving a round chambered in a hot rifle for more than 5-7 secs. Same goes for the ambient temperature being 30-50 degrees cooler. When I was reloading with RE-15 for matches shot in summer months, I would have to adjust 2-3 MOA at matches in the afternoon versus strings shot at 900am before it got hot.

I planned to switch to Varget because they claim it is less temperature dependent, but I discovered action pistol and 3 gun. I haven't shot a 600 yard match since then.

Definitly the next place to look. Sound advice from Phil.

 

[henschman]

Colder air is more dense, and creates more resistance for a bullet traveling through it, so it would make sense for you to hit low in colder temperatures, all else being equal. What really matters is ambient air density, but temperature is one of the big 3 variables that affects it (the others being humidity and pressure). How much temperature affects your POI at various ranges really depends on the load, like always, but a rule of thumb I have heard thrown around that seems to work well with standard rifle cartridges is 1 MOA for every 20 degrees, which would be spot on for the numbers you report (3 MOA low at 600 for a 50-60 degree lower temperature).

Any time you get to do any known distance shooting, bring a notebook and pen and WRITE EVERYTHING DOWN, along with the conditions that it was shot in. This way you will have more of a composite picture of what your rifle does under various conditions (wind, temperature, etc.), and you will know how to compensate. Just 2 data points to compare, like you now have, is very valuable information. You now have a good idea of how many MOA to compensate per degree, from the baseline temperature of when your rifle was zeroed: you know that for that particular load, you just use the rule of thumb of 1 MOA per 20 degrees.

 

[silver star]

Colder air is more dense, and creates more resistance for a bullet traveling through it, so it would make sense for you to hit low in colder temperatures, all else being equal. What really matters is ambient air density, but temperature is one of the big 3 variables that affects it (the others being humidity and pressure). How much temperature affects your POI at various ranges really depends on the load, like always, but a rule of thumb I have heard thrown around that seems to work well with standard rifle cartridges is 1 MOA for every 20 degrees, which would be spot on for the numbers you report (3 MOA low at 600 for a 50-60 degree lower temperature).

Any time you get to do any known distance shooting, bring a notebook and pen and WRITE EVERYTHING DOWN, along with the conditions that it was shot in. This way you will have more of a composite picture of what your rifle does under various conditions (wind, temperature, etc.), and you will know how to compensate. Just 2 data points to compare, like you now have, is very valuable information. You now have a good idea of how many MOA to compensate per degree, from the baseline temperature of when your rifle was zeroed: you know that for that particular load, you just use the rule of thumb of 1 MOA per 20 degrees.

Thanks for the info, good stuff.

 

[jtischauser]

Colder air is more dense, and creates more resistance for a bullet traveling through it, so it would make sense for you to hit low in colder temperatures, all else being equal. What really matters is ambient air density, but temperature is one of the big 3 variables that affects it (the others being humidity and pressure). How much temperature affects your POI at various ranges really depends on the load, like always, but a rule of thumb I have heard thrown around that seems to work well with standard rifle cartridges is 1 MOA for every 20 degrees, which would be spot on for the numbers you report (3 MOA low at 600 for a 50-60 degree lower temperature).

Any time you get to do any known distance shooting, bring a notebook and pen and WRITE EVERYTHING DOWN, along with the conditions that it was shot in. This way you will have more of a composite picture of what your rifle does under various conditions (wind, temperature, etc.), and you will know how to compensate. Just 2 data points to compare, like you now have, is very valuable information. You now have a good idea of how many MOA to compensate per degree, from the baseline temperature of when your rifle was zeroed: you know that for that particular load, you just use the rule of thumb of 1 MOA per 20 degrees.

I did not know this. Great rule of thumb right there.

 

[Mac MacDonald]

I handload all my rounds, except shotgun. I chrony my loads and know the feet per second (fps) at a given temp (if you dont reload, chrony about 20-rounds from your ammo supply and use that as your base). Once you know your fps you're golden. You can perform a bunch of math or use an app, on your phone, that uses your gps coordinates to account for elevation, temp., wind speed, barometric pressure, etc. This will tell you what your come-ups and drops are at any given moment in time. When I shot F-Class I used an app religiously.

Here is a link to the app I use http://ballistic.zdziarski.com/ pay the extra cash and buy the field edition. You won't be disappointed.

I may not be the best 3 Gunner, yet ;-) but I can shoot all x's in an F-Class match with my Remington 5R F-class rifle (check the link in my signature).

 

[Mac MacDonald]

I planned to switch to Varget because they claim it is less temperature dependent, but I discovered action pistol and 3 gun. I haven't shot a 600 yard match since then.

I use Varget for my .308, .243, 30-30, and 5.56. It is a great powder and is insanely consistent. It is not too sensitive to extreme heat but cold temps seem to effect it's performance. That being said, it is the most consistent powder I've used so far.

 

[TroyF]

Awesome rifle Mac!

 

[dennishoddy]

Some rifle powders can be very temperature dependent. When shooting 600 yds, you can throw off elevation 2-3 MOA just by leaving a round chambered in a hot rifle for more than 5-7 secs. Same goes for the ambient temperature being 30-50 degrees cooler. When I was reloading with RE-15 for matches shot in summer months, I would have to adjust 2-3 MOA at matches in the afternoon versus strings shot at 900am before it got hot.

I planned to switch to Varget because they claim it is less temperature dependent, but I discovered action pistol and 3 gun. I haven't shot a 600 yard match since then.

This!
Its amazing how enviromental conditions will have an effect on powders. I see some manufacturers are targeting this problem with new formulations.
I've experienced the same, shooting the same round, same powder at Okla levels vs high country elk hunting. Not only temps but altitude.

 

[KurtM]

"Changes in atitude, changes in latitude, nothing remains quite the same." Or so sang Jimmy Buffet, the king of long range shooting I can only assume.

 

[dennishoddy]

"Changes in atitude, changes in latitude, nothing remains quite the same." Or so sang Jimmy Buffet, the king of long range shooting I can only assume.

Or the long range Margaritta!