Powder temp sensitivity

[Popsbengo]

What do members of the forum think about the significance of powder temperature sensitivity specifically with regard to shooting in the UK ?

I use Vhit N140 & N540 in .308 and N570 in .338.  It's rarely colder than 5C and hotter than 25C and I've seen little variation in POI at 600yds. I've not attempted to chronograph cold/hot velocity, is it worthwhile?

[TJC]

1 hour ago, Popsbengo said:

What do members of the forum think about the significance of powder temperature sensitivity specifically with regard to shooting in the UK ?

I use Vhit N140 & N540 in .308 and N570 in .338.  It's rarely colder than 5C and hotter than 25C and I've seen little variation in POI at 600yds. I've not attempted to chronograph cold/hot velocity, is it worthwhile?

POI at 600 yards with the temp and powders you refer to is minimal ie 3”. At 1000 yards with the N500 series of powders you are talking close to a 35 FPS difference between 5-25C change, or 10 inches in POI. Effectively, it is 1 FPS change per 1 degree F change. It’s another variable you can control by either accounting for it through accurate data collection or by using a less temp sensitive powder (1FPS change is deemed very sensitive). With a 338 at greater distances than 1000 the effect will be magnified and the effect of temp on velocity isn’t always linear so as you get up into the high 20s the effect can be more marked making accurate data collection extremely valuable. 

 

[Popsbengo]

1 hour ago, TJC said:

POI at 600 yards with the temp and powders you refer to is minimal ie 3”. At 1000 yards with the N500 series of powders you are talking close to a 35 FPS difference between 5-25C change, or 10 inches in POI. Effectively, it is 1 FPS change per 1 degree F change. It’s another variable you can control by either accounting for it through accurate data collection or by using a less temp sensitive powder (1FPS change is deemed very sensitive). With a 338 at greater distances than 1000 the effect will be magnified and the effect of temp on velocity isn’t always linear so as you get up into the high 20s the effect can be more marked making accurate data collection extremely valuable. 

 

I'm aware of the theory and effects, I was more interested in the experience of others and the practical need to bother measuring variations. Out of interest where do you get your data from? Have you tested or are you reporting information you've gleaned from other sources? My understanding (received wisdom) is temp. variation is somewhat specific to calibers so not necessarily transferable in terms of x fps/degree.

[brown dog]

Pops,

Have a read of this old thread.   I think your answer's in there

 

 

[TJC]

My data is real world recorded here in the U.K. and the US. I take handloads and factory ammunition to both places and specifically record the effects. We often shoot matches in the US at 50F in the mornings and over 90-100F in the afternoons so it becomes critically important. 

As to your other question, I’ve seen similar effects in .308 and 6.5mm but I think a bigger variable than calibre is lots. They can vary considerably hence the benefit of buying same lot powders in bulk. 

Below is one example I’ve recorded that shows some readings. 

 

[Popsbengo]

28 minutes ago, brown dog said:

Pops,

Have a read of this old thread.   I think your answer's in there

 

 

Cheers Brown Dog, that's the sort of thing I was after. I suspect even if the tested data varies between batches etc it's a useful starting point.

[NigelM]

I run RL15 in a 6.5x47 Lapua. Temp sensitivity is 2fps/deg C. I run a sub 10 deg load at 39.5g and a 10 deg plus load at 39.3g. The rifle loves 2900-2920 fps and to keep it inside that band I find I need to run two different loads.

US powder makers are getting very good at making temp stable powders like Target and H4350 but the European makers are a bit behind. I will be trying RL16 over the next few months as that is said to be much better. I hope the rifle likes it!

[Chanonry]

Well, I wonder if there is more to this than powder temp sensitivity.

I definitely see effects in winter and at short range as well. Zero drops are measured by the inch.  Tends to be a zero shift than much variation on the trajectory itself. Now I don't have great data, but I am not imagining this.  I think,

Looking at even extreme temp swings say zero'd at 10C and shooting in -10C (not often that extreme but sometimes) then powder sensitivity does not explain these shifts.

Possible culprits include primer temp sensitivity; mechanical effects of cold on the rifle/scope; was the zero a true cold bore; zero shift over time (funny it always goes down).....

 

[Popsbengo]

17 minutes ago, Gluv said:

I have viht 165 at 0.8 fps per degree based on my own measurements, seems pretty accurate....I don't walk around with a thermometer just for fun you know ! 😉

Gluv🇬🇧

What you do for fun Gluv clearly is no business of mine.  Put that weasel down.. 😂 

 As a target shooter I'm not really expecting or needing a first cold-shot 'V' bull so the minimal differences between a British warm day and a cold day seem a bit academic. I do think it's important to keep your ammo temperature as constant as possible during a session, especially on sunny days (even been known at Eskdalemuir).  There's just so many damn variables  - brilliant isn't it!

[Popsbengo]

1 minute ago, Gluv said:

I don't think ammo temp really matters if shooting at 600 yards or so .When shooting long range , I know it makes a big difference . It's all the little things that add up to become a big thing at distance . 

Gluv🇬🇧

You're correct (oo that hurt me). We shall see how much on Monday 25th. 

[Popsbengo]

Just now, Gluv said:

I shall bring my thermometer gun and Tommy Robinson mug for you to swoon over 👍😂

Gluv🇬🇧

Oh you had to go and ruin it...  For that I'm going to put only EU approved ingredients in the chilli 😁  You will be so stricken with gas that it'll be a wonder if you hit anything past 300yds