Advanced Marksmanship Temperature sensitivity factor for AB39 and AB43 ammunition

[mberry223]

Hoping someone here has this data. I'm using iStrelok with good results. Now that the weather is warming up, I want to make sure I have the right data in the program. I know the powder in these loads is less sensitive than most, but I don't have any clue what number to input, the default is 1.4.

Anyone know the answer, or where I can find it?

Thanks!

 

[ShtrRdy]

You might just have ice down a few rounds, and also place a few rounds in the sun. Then using a laser thermometer, if you have one, measure the case temperature and fire the cold and hot rounds over a chrono.

 

[mberry223]

Thanks. Maybe I'm confused. I'm looking for a number that would represent the sensitivity. I've never seen it expressed that way before, so I very well could be imagining something that doesn't exist.

I received a PM from someone that knows their way around ballistics and they said their experience indicated 2 degrees per 1 foot of velocity.

For the purposes of the program, I'll try running that as 2.1 and see what it spits out.

 

[jdknotts1]

I left mine at the default 1.4 and it seemed to work just fine. Although I wasn't shooting in highly varying temps from one week to the next.

 

[mberry223]

I left mine at the default 1.4 and it seemed to work just fine. Although I wasn't shooting in highly varying temps from one week to the next.

We can compare at the comp next week. I'd hate to miss out on the advantage of a more stable powder. Kind of defeats the purpose of the advancement.

 

[damoncali]

Can you turn that feature off? Frankly, it's a goofy way to go about it. Measure the actual velocity at high and low temperatures and use that. Guessing based on some mathematical kludge is not going to be as accurate. If you must, use the data of those two points to estimate what velocity will be in between. It's probably the same thing the program is doing, but at least you'll know where you're guessing.

 

[mberry223]

Just to follow up in case anyone else ever has the same question, the solution is .3. On the program, there is a hot button that you press and enter in your velocity at two different temps. The information I was given said that they had seen a 1 fps difference per 2 degrees. I entered in my known velocity at one temperature, then raised the temp by 20 degress and added 10fps and the program spit out a temperature sensitivity factor of 0.3. Air rifles are listed as a 0, so 0.3 must be pretty good! Playing with the numbers and the firing solutions seem to be accurate based on my experience.

Thanks for the help!

 

[Mjolnir23]

Tag, been messing with that sensitivity factor myself quite a bit lately. I will give this a shot also and see how it does.

 

[jdknotts1]

I left mine at the default 1.4 and it seemed to work just fine. Although I wasn't shooting in highly varying temps from one week to the next.

I was wrong. It "seemed to work fine" in lower temps. Shooting the other day it got up to 85degs and I was up to .5mils off at 800 yds. I decreased the sensitivity and it started to sync up better. Definitely takes some messing with to get it right.