Let's Talk About MV Temp Tables In Ballistic Calculators!

[Steel+Killer]

First who uses this feature and how much of a difference does it make vs not?

Second I understand temperatures affecting powder burn rates and therefore affecting MV and that is what the MV Temp Table is for, but doesn't the Kestrel assume the ammo temperature is the same as the ambient/air temperature when calculating MV. Other words let's say you are on a hunt and the ambient/air temperature is 32F, but you just loaded your rifle with ammo that was in your pocket and close to your body temperature 98F or the sun warmed the rifle and also warmed the round in the chamber wouldn't that change the MV. I guess what I am getting at is it seems like in order for all this to be accurate the Kestrel needs to know the temperature of the ammo along with the ambient/air temp. Is that correct? @Kestrel Ballistics

 

[Dthomas3523]

The kestrel without temp table assumes bullet is moving at the velocity inputted at all times. For example, when MV table is turned off, and you have 2950 as your velocity in your profile, it always uses 2950. It then uses the current conditions and gives you data based on 2950 MV and current conditions. It assumes nothing. It could be -30 or 110 outside, and it still uses 2950.

When you use a temp table, you tell the kestrel that at X temp, the bullet is now going 2930, at y temp it’s 2950 and z temp it’s 2970.

With the table turned on, now the kestrel uses the current temperature and assumes your ammo is that temp and uses the appropriate velocity.

 

[Steel+Killer]

With the table turned on, now the kestrel uses the current temperature and assumes your ammo is that temp and uses the appropriate velocity.

That's what I am getting at with MV temp table turned on if your ammo is not at the current temp its going to throw it off slightly. Example you drive to the range in the summer 95 plus degrees with the AC blasting 70 degrees or less and your ammo is in the truck with you and hasn't had a chance to warm up.

 

[_Windrider_]

That's what I am getting at with MV temp table turned on if your ammo is not at the current temp its going to throw it off slightly. Example you drive to the range in the summer 95 plus degrees with the AC blasting 70 degrees or less and your ammo is in the truck with you and hasn't had a chance to warm up.

It’s gonna be off slightly either way. Point is to collect as much velocity data as possible and put it in the accuracy will be better that way.

 

[Steel head]

I use it for my 7mm, the distances I usually shoot will show a moderate change and it’s powder while pretty decently temp stable still does change.
I just chrony rounds when they’re at various temps and record the change.

 

[Steel+Killer]

So with all the other data that is collected by AB with their CDCs I am surprised they don’t have it to where you could input what kind of powder you have and then it could work that into the solution somehow. Seems like the burn rate for powders at different temps would have been analyzed by now.

Let me also say I get that when we’re getting down to this we are splitting hairs, but isn’t that what all this is about....

 

[brianf]

There is no substitution for record keeping as well as keeping your eyes open, no matter how good the program.

It’s freezing cold outside but your Ammo is warm/hot in sun etc

 

[Steel head]

So with all the other data that is collected by AB with their CDCs I am surprised they don’t have it to where you could input what kind of powder you have and then it could work that into the solution somehow. Seems like the burn rate for powders at different temps would have been analyzed by now.

It can change in different cartridges and pressure levels snd im sure other factors beymy pay grade.

Take R26, when I ran it hot I got a significantly larger temp swing than my current somewhat mild load.

 

[Steel head]

There is no substitution for record keeping as well as keeping your eyes open, no matter how good the program.

It’s freezing cold outside but your Ammo is warm/hot in sun etc

I’ve seen cartridges on a shooting mat in the sun be quite a few degrees warmer than air temp.

A lot of last year I took a temp gun with me.
Record temp and speed and log it in.
Poof- data for the kestrel and some things to watch out for.

 

[Dthomas3523]

Even burn rates will be off. There’s no way to know what that specific lot is doing. There’s also no way to know what the end user has done as far as storage and such.

You’d basically be adding more work for the same unknown results.

Also, what targets are you shoot that are small enough these tiny variations will matter and that you need a 1st round impact? We are getting into the area of unrealistic expectations.

 

[Deleted member 113831]

So with all the other data that is collected by AB with their CDCs I am surprised they don’t have it to where you could input what kind of powder you have and then it could work that into the solution somehow. Seems like the burn rate for powders at different temps would have been analyzed by now.

Let me also say I get that when we’re getting down to this we are splitting hairs, but isn’t that what all this is about....

The same type of powder changes temp sensitivity slightly lot to lot, then changes again once it acclimates to the climate you store it in.

That same lot of powder changes depending on case volume to bore ratio of the cartridge it is used in. (300Win vs 243Win for instance use some of the same powders).

Even the temp range can determine the magnitude. A certain powder might resist change really well from 0 degrees thru 40 degrees, then get a little more active from 40 degrees to 80 degrees, then get spikey from 80 to 100 degrees.

In the opposite situation, some temp resistant magnum powders resist change at hotter temps, but don't ignite well at all in colder temps. This can raise pressures because the powder column resists burning and just adds to the total weight of the ejecta. In this situation, you get a combination that actually has HIGHER pressures at low temp.

 

[Holliday]

That's what I am getting at with MV temp table turned on if your ammo is not at the current temp its going to throw it off slightly. Example you drive to the range in the summer 95 plus degrees with the AC blasting 70 degrees or less and your ammo is in the truck with you and hasn't had a chance to warm up.

Yep. I run a label on my hunting rifle for my elevation 70° warm hunt day. On the label I also have a 30° cold weather, cold ammo, delta. I usually keep mindful of how my ammo temp is changing on a cold day. If the ammo is warm, I usually split the difference. Seems to work well.