Changing ammo to maintain zero across temps

[RTH1800]

Has anyone ever expiremented with using hotter lots of RF ammo in cooler weather to maintain a consistant velocity and stay closer to a consistant zero?
At the range I realize you just shoot the most accurate ammo. For precision hunting you do not always have a chance to check zero immedately before the hunt. Would it make sense to simply use a bit faster ammo on a cool morning?

 

[_Windrider_]

Has anyone ever expiremented with using hotter lots of RF ammo in cooler weather to maintain a consistant velocity and stay closer to a consistant zero?
At the range I realize you just shoot the most accurate ammo. For precision hunting you do not always have a chance to check zero immedately before the hunt. Would it make sense to simply use a bit faster ammo on a cool morning?

Here is what i would do. Zero the rifle for the flattest shooting of the loads you will be using. Then without changing your zero, shoot the other loads and not the offset. with that info, you can build very reliable field cards. Truth be told, at 100 yds you wont see a significant change, but as the ranges increase you obviously would. but thats why we have BC's.

 

[6.5SH]

Here is what i would do. Zero the rifle for the flattest shooting of the loads you will be using. Then without changing your zero, shoot the other loads and not the offset. with that info, you can build very reliable field cards. Truth be told, at 100 yds you wont see a significant change, but as the ranges increase you obviously would. but thats why we have BC's.

This also allows you to use your zero stop if so equipped.

 

[_Windrider_]

This also allows you to use your zero stop if so equipped.

that too

 

[Nodakplowboy]

Get a dedicated hunting rifle that shoots dedicated hunting ammo.

 

[RTH1800]

I think you missed the point. With temperature changes, velocity changes. I am trying to find a way to use ammo to correct the difference. If I dial in at 75 degrees and hunt on a 25 degree morning using the same data.

 

[_Windrider_]

I think you missed the point. With tempature changes, velocity changes. I am trying to find a way to use ammo to correct the difference. If I dial in at 75 degrees and hunt on a 25 degree mourning using the same data.

Honest question, what ranges are you taking shots at?

 

[RTH1800]

Muzzle to 125 yards or so. All headshots.

 

[_Windrider_]

Muzzle to 125 yards or so. All headshots.

Don’t even worry about. You will not see any change at 125 yards.

 

[RTH1800]

I do absolutely see changes. That is the point.

 

[RTH1800]

At 100 yards every 10 FPS change in velocity is 1/4" vertical spread. So, if you go 40 FPS you are talking about 1".

 

[ma smith]

Don’t even worry about. You will not see any change at 125 yards.

I don't believe this is correct for rimfire, IIRC the come up on 22LR from 55 to 100yds is already ±1.8mils at constant temperature. Seems it would be easier to run a different ballistic card for 25 and 75? To make this work perhaps put your zero stop at -.5 to reset zero with out also doing zero stop (some scopes are more of a hassle to do ∆ stop than vs just turret zero).

 

[RTH1800]

My interest is to see if anyone has used ammo to maintain consistant POI over varying temps.
I am not interested in other options or debating that it makes no difference.

Thank you.

 

[_Windrider_]

I don't believe this is correct for rimfire, IIRC the come up on 22LR from 55 to 100yds is already ±1.8mils at constant temperature. Seems it would be easier to run a different ballistic card for 25 and 75? To make this work perhaps put your zero stop at -.5 to reset zero with out also goidn zero stop (some scopes are more of a hassle to do ∆ stop than vs just turret zero).

yeah, but we are not discussing rimfire.

EDITED TO ADD: IM A DUMBASS AND MISS THE RF PART OF THE ORIGINAL POST.

 

[RTH1800]

We are absolutely discussing rimfire as stated in the opening sentence and we are in the RF section. Thanks.

 

[_Windrider_]

My interest is to see if anyone has used ammo to maintain consistant POI over varying temps.
I am not interested in other options or debating that it makes no difference.

Thank you.

copy that, good luck. i think you are chasing waterfalls. just as an aside, as i know you dont want my opinion, you could just plug numbers in JBM and see where the drops change and at what velocity temp. but i reiterate, at 125 yards it doesnt matter. but im also wrong a lot.

 

[_Windrider_]

We are absolutely discussing rimfire as stated in the opening sentence and we are in the RF section. Thanks.

OH HOLY SHIT! See, im wrong. I didnt even see RF. Ignore everythiung i said. sorry to derail this

 

[RTH1800]

No problem I enjoy many of your post and insights.

 

[264win]

Interesting idea.
I have experimented with running different ammo for summer and winter, but not different lots of the same ammo.
Are there significant speed differences in quality match ammo lots ?

 

[RTH1800]

Yes,
Eley Match and Eley Tenex are marked with test gun velocity on box. It is normally lower that what the actual velocity is in my rifles. From memory I think it varies from 1045 to over 1080 or a bit higher. I will check my lots tonight. I always put it on shelf in order of ascending velocity.

 

[b6graham]

Interesting idea.
I have experimented with running different ammo for summer and winter, but not different lots of the same ammo.
Are there significant speed differences in quality match ammo lots ?

Yes. Could be 30-40fps from one lot to another

 

[Near miss]

All my ammo lots have recorded MV for few different temperatures.

I use it and have found it to work excellent.

I think finding a lot that starts the MV from where the other ends will be a challenge, not to mention that they might have horizontal offset.

To keep ballistic variables to minimum, you should use the same ammo and finding just the right velocity will be hell, I mean lot testing in it self is already hard, to include that it must run at certain MV.. It does not sound easy.

 

[grauhanen]

Has anyone ever expiremented with using hotter lots of RF ammo in cooler weather to maintain a consistant velocity and stay closer to a consistant zero?
At the range I realize you just shoot the most accurate ammo. For precision hunting you do not always have a chance to check zero immedately before the hunt. Would it make sense to simply use a bit faster ammo on a cool morning?

Muzzle to 125 yards or so. All headshots.

Using "hotter" lots of ammo for headshots out to 125 yards to make up for an expected velocity drop due to cooler morning temperatures is likely to be frustratingly difficult.

The reason why is that it's impossible to predict the MV of an individual round, regardless of whether its from a hotter lot or not. The average MV of a lot of ammo is not the MV of any particular round, it's the average obtained in testing. The first round in the chamber, whether it's from a hotter lot or not, won't have a MV that is knowable unless it's chronographed. The only thing that can be said is that it should be within the ES of the box of ammo from which it came. Standard velocity match ammo will have the smallest ES, but it can easily be over 30 fps.

Anyone concerned that slower MVs due to cooler morning temperatures will cause a missed headshot at 125 yards might do well to get a bit closer to the target. Using different ammo is not sufficiently reliable for one shot accuracy. In any event, if the expectation is that morning temperatures are sufficient to cause a significant reduction in MV, aim a wee bit higher or adjust the scope a little.

 

[RTH1800]

Since we are discussing small differences it seems I can find transistions or zones that are within an acceptable deviation.

 

[RTH1800]

Using "hotter" lots of ammo for headshots out to 125 yards to make up for an expected velocity drop due to cooler morning temperatures is likely to be frustratingly difficult.

The reason why is that it's impossible to predict the MV of an individual round, regardless of whether its from a hotter lot or not. The average MV of a lot of ammo is not the MV of any particular round, it's the average obtained in testing. The first round in the chamber, whether it's from a hotter lot or not, won't have a MV that is knowable unless it's chronographed. The only thing that can be said is that it should be within the ES of the box of ammo from which it came. Standard velocity match ammo will have the smallest ES, but it can easily be over 30 fps.

Anyone concerned that slower MVs due to cooler morning temperatures will cause a missed headshot at 125 yards might do well to get a bit closer to the target. Using different ammo is not sufficiently reliable for one shot accuracy. In any event, if the expectation is that morning temperatures are sufficient to cause a significant reduction in MV, aim a wee bit higher or adjust the scope a little.

I agree with your statements about SD etc. I do not agree with your conclusions.

I am not so concerned about "cooler morning air" as I am with hot, warm, cool and cold seasons, all of which I hunt in. In the midwest tempatures can vary from 120 deg to -20. I do not hunt the extrems but I do hunt from 20 to 90 degrees.

I will work up some data and post it here when I get it figured out.

 

[littlepod]

With a given lot of ammo, and a zero at say 25 yards. The ammo going at 1000fps and 1080fps isn't going to have much shift in zero.

So if you know what the velocity is due to different tests in temperature, just plug it into your calc and you'll know how it'll affect your POI at 125 yards. So for example on a hot day your round is 1099fps, and you'll be at say 1.7mils at 100yards. On a cold day at 1025fps, you'll be at 2.2mils at 100 yards. So if you have data/test on the ammo you are using, you'll know your proper adjustment based on the temperature.

Now at 125yards, you also have things like the atmospherics come into play. If I really wanted precision hunting, I'd just carry my kestrel, have accurate MV-Temp and be good to go.

Am I answering the right question? For our 2-day matches, this happens quite a bit. We start on a cold morning at 40 degrees, and by the 2pm with us baking in the sun at 80 degrees, the bullets have diff velocity and we account for it shooting out to 300 yards.

 

[RTH1800]

Not sure how to say this. I’m not interested in your ideas other than using ammunition to maintain point of impact in changing temps. And yes 80 FPS is the 8/10 of an inch at 100 yards.

 

[littlepod]

The most I can think of is using SK LRM at 1110 fps, and a slow lot of SK+ running at 1055. In the cold, SK LRM could drop velocity down to similar to SK+ in normal temps.

 

[RTH1800]

Eley is available in a rainbow of velocities.

 

[RTH1800]

My shelf has velocities listed from 1043 to 1084.

 

[Klay23]

I’m sure this can be done but it would be tedious. And I think accuracy could suffer. “Most” match ammo is going to be say 1080-1030fps. Not sure how much drop that would have and how much temp would need to change to make that work. But maybe find something like federal automatch which I don’t think is subsonic and then something like center x which is going to hover around 1080. I’m sure there are better examples but it would be work to figure out temp and FPS drop

 

[beetroot]

Biggest question is what sort of error are you currently seeing and what can you tolerate?
What ammo are you currently using?

Yes in theory this will work but you could well run into POA/POI issues.
I'd buy a few different packets of ammo and test it, that's the only way to know for certain.

The theory is sound so actually testing it is the only way to know for certain

 

[Gleedus]

I realize your not interested in other Ideas. So please bare with me and I will answer your question.
I have no idea what experience you have with using and acquiring drop data.
Using a ballistic app is very simple its accurate and if your only shooting 125 yards your data can be off quite a bit before the prediction is outside of your group size/velocity ES. As littlepod noted we use this in matches for much further distances very successfully.
Some apps have a option to enter your Zeroing environmentals and then account for that as well. (Something I dont use)
Looking at 125 yards from 0⁰c-25⁰c (32⁰f- 77⁰f) the velocity change is approximately half of the total elevation shift the other half is due to air temp/air density. In order to do this with ammo velocity you would need to use double the actual velocity difference to equal the same drop unless you still use a app to account for air temperature changes. In which case you may as well just use the app.

Now does this actually work? The short answer is no. I have done testing looking at lots and their effects down range. BCs are not always consistent lot to lot even at the same velocity but normally very close. If we look at the drag coefficient from 1000 fps to 1300 there is a huge change so your measured drop at 100 yards does not perfectly correlate to velocity with out a BC change. If for instance we were always looking for 1070 fps this wouldn't be a issue but if we are to account for weather changes as well then our starting velocity will not be the same.
If we hit cold weather and your 1070 lot drops to 1040 you would need your 1130 lot that has now dropped to 1100 to have POI the same. But now with the higher velocity you have more time of flight at a higher drag because of the increased velocity further complicating it. You might be on at 100 yards and off at 50.

Now having said that there is some valid reasons to run a winter ammo and a summer. In my tests at 200 yards Eley force in the winter shot better then contact but as the weather warmed up and velocity increases the contact the shot the same as the force did at the same velocity. The force now at the higher velocity didnt shoot as good. But the drop data is different due to air temp changes yet.

Go have some fun and test it shoot 100, 125, and 150 yards and measure actual drop. You will find some interesting things if you try a bunch of different ammo and how it tracks with velocity and a ballistic calculator.

 

[ma smith]

If you can shoot an unkown distance target at 2moa you are a pretty dang good shot, in terms of using 22LR





[Talking about UKD > 100yd]

 

[grauhanen]

Eley is available in a rainbow of velocities.

My shelf has velocities listed from 1043 to 1084.

You say that like you believe it's possible to pick and choose a particular MV by picking a box of ammo with a certain MV printed on it. That doesn't assure you of a thing because that's not how it works.

Those are the average MVs of a number of rounds in the Eley test barrels. They are not the MV of each round in the box. MV will vary from round to round, with some faster, some slower. Average MV can vary from rifle to rifle. You can't know what the MV is in your rifle until you check it with a chronograph.

 

[RTH1800]

Amazing grasp of the obvious.

 

[jLorenzo]

I think it would be easier, more effective and more consitent to use the same ammo and dial the changes in drop using a good ballistic calc to figure out the difference.

 

[sarcasmn]

I would think this is where a dope (data on previous engagements) book would be useful. You'll need to go out and shoot in the conditions you are expecting and records those results. This may take a little time for hunting because things will change as your rifle heats up. For my hunting rifles I shoot them in various conditions and always record the so called cold bore shot as this is the shot you will likely be taking when hunting. Now if you are hunting squirrels or something where you will take multiple shots at then the data on successive shots will be pertinent. I have gone so far in cold weather to wait as long as half an hour between shots to see what a really cold barrel will do.

I live in Georgia where it is hot in the summer and gets below freezing in the winter. I am going to try using biathlon ammo this year to see how it works in the colder months as an experiment. I can't see how you are going to get the results you want without going out in the environment you are planning and recording solid dope for those conditions with that specific ammo.

 

[ballisticdaddy]

I have ran quite a bit of rimfire ammo across a Labradar and have found 50 fps difference between boxes within the same lot, within the same brick. Even if you listed each lot by MV as you have suggested there is no way to ensure consistency within each lot over the temp range that you are referencing. I believe every post in this thread was members trying to assist but seems you have an amazing grasp of the obvious

 

[RTH1800]

Some things are obvious to me.

If you are getting 50 FPS ES you are shooting sub optimal ammo.

It’s also obvious you either cannot read or ignore what you do read. I have no interest in your or other opinions. Simply don’t care at all. I clearly ask for experience with a very specific topic.

 

[ballisticdaddy]

Some things are obvious to me.

If you are getting 50 FPS ES you are shooting sub optimal ammo.

It’s also obvious you either cannot read or ignore what you do read. I have no interest in your or other opinions. Simply don’t care at all. I clearly ask for experience with a very specific topic.

Lapua Center-X, SK Rifle Match + SK Long Range.....sub optimal Good luck chasing your tail!

 

[RTH1800]

Try some Eley Tenex.

 

[Booner1334]

Has anyone ever expiremented with using hotter lots of RF ammo in cooler weather to maintain a consistant velocity and stay closer to a consistant zero?
At the range I realize you just shoot the most accurate ammo. For precision hunting you do not always have a chance to check zero immedately before the hunt. Would it make sense to simply use a bit faster ammo on a cool morning?

I think the simple answer is yes, use the hotter ammo, as it would possible reduce one of the many different variables when shooting in warm vs cold temperatures.

Off the cuff, I can think of at least 4 different variables, some of which you have no control over, that will effect your poi. In general, I think the only way you're going to come close to the same point of impact in various temperature situations is from your dope. Nothing is better than practice.

1. Air density- cold, dry air being more dense than warm, moist air; use 'hotter" ammo in the winter to reduce the loss in velocity when shooting in colder, denser, more resistant air. This is where a ballistic calculator may be of help.
2. Keep your ammo warm to help reduce the variance in velocity caused by the temperature sensitivity of the powder and to keep the lube soft.
3. Does your rifle shoot differently when it's cold vs when it's warm? Maybe try a barrel tuner to mitigate changes in velocity and/or harmonics due to temperature changes. Keep your firing pin dry so the oil on it doesn't slow down ignition speeds.
4. Do you hold the rifle differently when you're wearing gloves and a heavy coat?

 

[BisSilent]

Has anyone ever expiremented with using hotter lots of RF ammo in cooler weather to maintain a consistant velocity and stay closer to a consistant zero?
At the range I realize you just shoot the most accurate ammo. For precision hunting you do not always have a chance to check zero immedately before the hunt. Would it make sense to simply use a bit faster ammo on a cool morning?

I'm sure someone has is the answer to the 1st question.

No, is the answer to the 2nd question. Use a ballistic app and don't be a dumbass!!!

 

[RTH1800]

Slow day in the trailer park?

 

[b6graham]

I'm sure someone has is the answer to the 1st question.

No, is the answer to the 2nd question. Use a ballistic app and don't be a dumbass!!!

reading comprehension a bit much for you i see

 

[BisSilent]

reading comprehension a bit much for you i see

Naw!!! It's just a stupid idea...that's why the scopes have turrets.

I equate it to taking the door hinge pins out to get out the door when all you needed to do is turn the door knob

 

[b6graham]

Naw!!! It's just a stupid idea...that's why the scopes have turrets.

I equate it to taking the door hinge pins out to get out the door when all you needed to do is turn the door knob

so your turrets and ballistic app are 1000% going to give you the zero offset and dope thats perfectly repeatable with one lot of ammo shot at 80 degrees and another lot shot at 25 degrees

 

[BisSilent]

so your turrets and ballistic app are 1000% going to give you the zero offset and dope thats perfectly repeatable with one lot of ammo shot at 80 degrees and another lot shot at 25 degrees

My money is on Applied Ballistics being 1000% better at it than y'all!!

I hope you're Trolling and really not that stupid!!!

You said it yourself earlier that you can have 30-40 fps speed differences in the same box of ammo.

 

[...]

honestly, trying to match ammo to the temperature to keep zero sounds like a lot more work than figuring out what your dope will be on 1 lot of ammo for any given temp....

at most i could see having a "winter lot" and a "summer lot" of ammo.....but saying "im going to shoot Eley tenex at 80*, and Lapua midas at 70* and eley black box at 60* and Lapua polar at 50*" sounds like a fuck ton of work.


personally i like to reduce as many variables as possible, and the brand, and more specifically, the lot of ammo, is the biggest variable we have in rimfire.