Vihtavuori N160 temperature stabilty

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AndrewJS

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Hi, Has anyone seen a noticeable increase in pressure with N160 in hot weather? (30°C+)
I have reloaded for over 40 years and this has to be the worst powder I have used, but I may simply be shooting on more hot days.....
I am running105gr Bergers in a 243 at 2950fps and 162gr ELDMs at 3050fps in a 32" 7-270 WSM.
In the recent scorchio weather I had stiffer bolt lift and ejector marks in the afternoon when the temperature peaked. (The ammunition was kept in the shade as much as possible).
Below 20°C and I have no problems with N160.
Sadly my stock of H4831 and H1000 have gone and I'm wary of what's listed as "temperature stable".
Cheers Andrew
 
Just about any powder will increase pressures as ambient temperature increases.

In the old days “Tropical Cartridges” were a very real thing and were loaded to take into account working 30 plus degree temperatures of the tropics.

Modern powders are more stable and less temperature sensitive than older powders, but they still vary.

Was having a conversation yesterday with a friend who has found that some of his shoot really well in the winter, but not so well in the summer.

Following on from your post, I suspect that the velocities in the summer time will be a bit higher due to temperatures. This seems logical, as in some cartridges a tenth or two of a grain can make all the difference in group size. But a slight change in pressure thanks to ambient temperature could well have the same effect.
 
I’ve found N160 to be less forgiving in .243 - much more forgiving in .260 rem. Now using it in 6.5 CM and it seems well suited. I think it might be a quirk of the smaller bore, maybe try and find a node slightly below where you are or another powder?
 
This paper makes interesting reading.


It shows that most of the powders tested increase by 2 fps per degree centigrade increase in temp from 1°C to 36°C. So an increase of about 70 fps over that range. If you consider that an increase of 0.2grain of powder can be the difference between showing signs of pressure and not, running a load a touch below pressure signs on a normal Scottish day in the mid teens could easily start showing pressure signs at temperatures well into the 30s

It was part of a thread a couple of years ago

U

Thread '11 powders tested for temperature stability in 308 Win'

Thought this may be of interest to some...


Anyone want to buy some N140 and CFE223?

:-|:p
  • Like
 
Thank you all for commenting. I will drop back and look for a lower node to allow for these short heatwaves that seem to have become the norm here in the southern England.
I think I haven't noticed pressure problems before smply because I didn't shoot on really hot days. Places like Diggle were never hot!
 
Heym SR20 said:
This paper makes interesting reading.


It shows that most of the powders tested increase by 2 fps per degree centigrade increase in temp from 1°C to 36°C. So an increase of about 70 fps over that range. If you consider that an increase of 0.2grain of powder can be the difference between showing signs of pressure and not, running a load a touch below pressure signs on a normal Scottish day in the mid teens could easily start showing pressure signs at temperatures well into the 30s

It was part of a thread a couple of years ago

U

Thread '11 powders tested for temperature stability in 308 Win'

Thought this may be of interest to some...


Anyone want to buy some N140 and CFE223?

:-|:p
  • Like
Click to expand...
Interestign. I guess this makes load development in the warmer months of ones hunting climate preferable, to exactly minimize that risk.

Come the colder months, going to the range to make a poi shift test might then be a good idea however.

i do wonder how much fill rate% also might play a part in this. Normally a 95% FR or above is encouraged, no? but maybe going very close to 100% makes the loads more suceptible to pressure jumps in warm weather?
 
Scipio said:
Interestign. I guess this makes load development in the warmer months of ones hunting climate preferable, to exactly minimize that risk.

Come the colder months, going to the range to make a poi shift test might then be a good idea however.

i do wonder how much fill rate% also might play a part in this. Normally a 95% FR or above is encouraged, no? but maybe going very close to 100% makes the loads more suceptible to pressure jumps in warm weather?
Click to expand...
In my experience (way milder climate here) the 100 series Viht powders are more temp stable than the 500 . And (just a personal thought) I avoid too the full decades (130/140/160) and prefer those wich are in the middle (135 150 165). May be a stupid thought but cause the older powders are so well-knowed and, older on the market, those are top sellers and variation between diff lots may occurs easily.As per filling I try keeping it between 93/97,% but do not tear my hair out if a particular load need a light compressed 100% to 104% charge.
 
Motard said:
In my experience (way milder climate here) the 100 series Viht powders are more temp stable than the 500 . And (just a personal thought) I avoid too the full decades (130/140/160) and prefer those wich are in the middle (135 150 165). May be a stupid thought but cause the older powders are so well-knowed and, older on the market, those are top sellers and variation between diff lots may occurs easily.As per filling I try keeping it between 93/97,% but do not tear my hair out if a particular load need a light compressed 100% to 104% charge.
Click to expand...
Thank you very much for the real life feed back and experience Motard :-) Ah ok, so you arnt too worried about going over 100% then. Interesting. As a new reloader i am a bit nervous about that, but in time that might change, i guess. 🤠
But staying on the course of this thread, do you think that there might be a corelation between Fill rate and the effect of raised temps?

PS.And following on from this, how does one really know what ones Fill rate really is?
Because i took some loads from xxlreloading.com, where they use on reloading program i assume, and inserted the same cartridge, projectile and powder weight values into Gordons reloading too, and there were some %s difference in fill rate.
So how does one know just what the fill rate really is? I mean i guess it is easy to see if it is compressed or not, but i am not sure most reloaders can spot if they're dealing with a 92% FR or 95% ot 102 or 104? .:-|
 
Scipio said:
Thank you very much for the real life feed back and experience Motard :-) Ah ok, so you arnt too worried about going over 100% then. Interesting. As a new reloader i am a bit nervous about that, but in time that might change, i guess. 🤠
But staying on the course of this thread, do you think that there might be a corelation between Fill rate and the effect of raised temps?

PS.And following on from this, how does one really know what ones Fill rate really is?
Because i took some loads from xxlreloading.com, where they use on reloading program i assume, and inserted the same cartridge, projectile and powder weight values into Gordons reloading too, and there were some %s difference in fill rate.
So how does one know just what the fill rate really is? I mean i guess it is easy to see if it is compressed or not, but i am not sure most reloaders can spot if they're dealing with a 92% FR or 95% ot 102 or 104? .:-|
Click to expand...
hi Scipio, for developing a new load from start I use two reloading programs: Ql (paid vers) and Gordon Reloading Tool free (the owner unfortunately passed away but program still there, will add link at message end). Mind this not exclude a previous work on manuals (paper & web) from from both, powder and bullet, to acquire the starting load. Once You got it (starting load) You need measuring the internal volume of the brass you intend use possibly once shooted and reformed. This is easy: weight the empty case and then again it filled with H2o (dome stile at the mouth) and write down the difference. Adding this data to the new reloading project on both programs youll have a rough but thrustable filling ratio. Both Ql & Gordon's runs a complete lists of rather all the powders & bullets on the market (if not there is way to add new comers) and make the computing for You with the also the OAL you are whanting to use. But at the end youll fill a compress load just by hands, when you seat the bullett ad you ear crickets calling from the case 🦗🦗🦗🦗 😃
 
Last edited:
Motard said:
hi Sciopio, for developing one all new load I use two reloading programs: Ql (paid vers) and Gordon Reloading Tool free (the owner unfortunately passed away but program still there, will add link at message end). Mind this not exclude a previous work on manuals (paper & web) from from both, powder and bullet, to acquire the starting load. Once You got it (starting load) You need measuring the internal volume of the brass you intend use possibly once shooted and reformed. This is easy: weight the empty case and then again it filled with H2o (dome stile at the mouth) and write down the difference. Adding this data to the new reloading project on both programs youll have a rough but thrustable filling ratio. Both Ql & Gordon's runs a complete lists of rather all the powders & bullets on the market (if not there is way to add new comers) and make the computing for You with the also the OAL you are whanting to use. But at the end youll fill a compress load just by hands, when you seat the bullett ad you ear crickets calling from the case 🦗🦗🦗🦗 😃
Click to expand...
Thank You Motard! :-) And i have Gordons reloading tool! I do not have QL however, but if i also counter check with books, and online sites, (containing reloading program calculated loads), such as xxlreloading, and then of course build up loads safely, i think it should be fine. :) - I think i might wait to go for "a concert of the crickets" before i get more experienced however haha ,D
 
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