Strelok temp sensitivity factor

[StockDog]

What formula are you guys using to get tge "Temp sensitivity factor in %".

I took info from the other thread with change in fps of 50 fps change between 0 and 125*. I divided the change in temp by 125 to get my best guess.

Either

50 fps change / 125 = .4. >> Or 4%

I can also see the following.

2580fps velocity //50 fps change = .019. >> 1.9%

Strelok
308
175 SMK
42.9 RL 15
Velocity 2580

 

[Starosta]

There is a description of this formula on Strelok+ page:
www.borisov.mobi/StrelokPlus/

Without any guarantee but it makes sense to me this should be valid for all Strelok versions.

4. On how many percent bullet speed will change at change temperature on 15 degrees:
Suppose, you have 2 bullet velocity mesurement. 1 and 2 (for different temperatures):
TempDiference = temp_2 - temp_1;
SpeedDiference = speed_2 - speed_1;

TempModifyer = SpeedDiference/TempDiference*15/speed_1*100;

TempModifyer - this is parameter we need for input to my ballistic calculator.
2.5% - this is for very middle quality powder. Best powders can have 1.2 or so.

Hope it helps.

 

[Joop]

There is a description of this formula on Strelok+ page:
Strelok+.Ballistic calculator for Android

Without any guarantee but it makes sense to me this should be valid for all Strelok versions.

Hope it helps.

This is what I found, as well. I've just started using Strelok over this last summer. I've been using 1.2 recently and it seems to work well. I have not shot in any huge temp swings, yet (probably only 30-35* total), but it's been accurate, so far. The true test will be in another couple months when temps are 60-70* lower than my initial zero.

 

[StockDog]

It has been very close for me too. I use the knights program as well. It allows for atmospheric changes but not temp changes with powder. I don't think it matters that much between 40 and 90* under 800 yards.

I am going to compare actual data and make adjustments. I'll reconfirm the zero and confirm velocity with drops.

Thank you both very much

 

[Joop]

Bumping this thread just to relate an experience I had the other day. So far, it was the coldest day I've shot while using Strelok (42 degrees). I've been working on a load using H4831sc for my 6.5x55 Tikka. I finally got the velocity nailed down with my chronograph and my measurements on paper. However, Strelok was still a bit off (like .3 mil at 550 yards, so quite a bit!). I checked all of the data, a few times over and all appeared to be correct. Given the temperature swing, I thought I might play with the sensitivity factor to see how much of an effect it would have. In short, I ended up setting it to "0" (was using 1.2, before) and it was dead on with my chrony/hard data. Even when set to zero, I noticed that it still changes the trajectory a small amount, but not nearly as much as the 1.2 setting. It was calling for a lot more drop than I was getting, but after setting it to zero, it was on the money, like I said. So, while I'm still not completely educated on how this setting works, I would recommend playing with it a bit and see what works for you. On the plus side, my load is staying faster at cooler temps than I had anticipated, which is always a good thing, especially up here in the winter.

John

 

[Deleted member 10043]

I was going to start a new thread if nothing came up with a search. Zero is obviously disabling the function but for those that are anal I have been using .3% for H4831. A very immaterial difference but a difference it does make...

So, I enter the actual measured difference and Strelok calculates the %. Also, the OP incorrectly converted .4 to 4%. .4=40%. He should had stopped at .4 and used that. I have not backed into how Boris uses the .3 to calculate muzzle velocity based on current temperature. But we can divide the difference above and see the difference is not .3%. He is using it as factor in a formula to get the quotient above.

 

[TRAC]

I is some testing regarding this feature on strelok with 2 factory ammo in last 2 years.
First of all it works very well IF YOU INPUT CORRECT DATA.
This app is doing an linear interpolation, for this needs at least 2 valid / verified values to interpolate in between.
My advice is not to use any arbitrary % or out of internet factor.
Is well known the fact that powders are not affected by temperature in a linear way, from 0 C/ 32 F to 10 C/ 50 F you can have a very stable temp with low muzzle velocity change but over 15 C / 59 F to have some spikes also over 25 C / 77 f to have another jump, this is the reason you need valid data for all temp range you are shooting in.
If you use a data book and record muzzle velocity or drops in different environmental conditions is easy to get a muzzle velocity for a specific temp.
Ideally is to have a measurement at each 5 C / 40 F change work between your temp extremes an input in strelok only this who make sense.

For example if you get
850 m/s at 0C
853 m/s at 5C
859 m/s at 10 C
870 m/s at 15 C
884 m/s at 20 C
898 m/s at 25 C
928 m/s at 30 C
931 m/s at 35 C
notice this spikes, jumps in speed use them in Strelok as references, intermediary data will be close enough, is no need to input 850 at 0 C also 857 at 10 C because if you use 850 at 0 C and 870 at 15 C and you interpolate for 10 C (strelok will do this for you) you will get 863 m/s close enough from 859 m/s (what you got in the field), closer the measured values, closer to reality results.
From my testing I got to the conclusion this app needs at least 4 known values to be able to get correct results, maybe with stable powders needs less.

Mine is like this, yes I know very unstable powder, is Lapua factory ammo.

 

[Deleted member 10043]

Thanks for clearing that up. I went back and checked my settings and I have consider powder temp turned off so my % is not only incorrect I'm not even using it.

 

[Deleted member 113831]

With the multi-BC funtion and the ability to record actual multiple velocity windows affecting powder burn rate, Strelok Pro has been by far the most accurate program I have. I have AB and 4DOF on my phone as well. I have compared them all extensively and Strelok is not only equal to, or better in the accuracy dept, but the user interface is by far the easiest to navigate.

 

[1jonathan1994]

I use AB but strelok is good if you input good data.
Compared streloks formula to its outputs and I figured out they have a Fahrenheit to celcius conversion wrong in the software.

What the formula says to use or what you calculate is actual - You multiply that by 5/9 for C/F.
Factor x 0.56 = strelok %
Usable values are .09 - 0.14 for Hodgon extreme and IMR enduron powders.
.17 - .28 for most good single base stick .
.3 - .4 for temp sensitive stick.

.5 -.8 should be close for ball powder.

Edited data.

 

[Conaso]

Have you notified Igor Borisov of your discovery?

 

[Deleted member 10043]

I use AB but strelok is good if you input good data.
Compared streloks formula to its outputs and I figured out they have a Fahrenheit to celcius conversion wrong in the software.

What the formula says to use or what you calculate is actual - You multiply that by 5/9 for C/F.
Factor x 0.56 = strelok %
Usable values are .4 or less for Hodgon extreme and IMR enduron powders.
.8 for most regular single base.
1.2 should be close for ball powder.

That is way too high. .1 for Extreme and Enduron. .2 to .3 for other single base.

 

[1jonathan1994]

Have you notified Igor Borisov of your discovery?

No. I quit strelok way back.

 

[1jonathan1994]

That is way too high. .1 for Extreme and Enduron. .2 to .3 for other single base.

You are correct. I went back to my work and I was using 0.17 for factory hornady based on observed data and the 5/9 correction.
I'll edit above.

 

[sabrecross]

Have you notified Igor Borisov of your discovery?

I posted 1Jonathoan1994 observation on Igor Borisov's Strelok's FB page and asked him to take a look at it.

 

[Conaso]

sabrecross - good man!

 

[Mattio]

I use strelok successfully by keeping my sensitivity factor at 0 or .1... shooting from 40-90 degrees hasn't made much of a difference for me.