Load development in hot weather ??

[280AIDave]

i am about to start working up a new load and with the 85 Deg + heat does anyone have advse ?
The guys in the south deal with it all the time. Do you have to re-work the loads once hunting weather or cooler-cold conditions come around ?

 

[Bbear]

Temps in hunting season here in my part of Texas may run from the sub-freezing mark to 80 degrees. Even temp-insensitive powders, you'll see a change in the grouping and in the drop at distance. If the majority of your shots are inside of 300 yards, no big deal. If, however, you are loading for BR, you'll need to re-do your loads. You may only have to tweak the powder drop a tenth or three grains of powder, but it's there and it will make a difference from being ON a node and being off of one.

 

[T-shooter]

Try chronographing the loads in hot weather and in colder weather, try to match the same average velocities.

 

[338 dude]

i am about to start working up a new load and with the 85 Deg + heat does anyone have advse ?
The guys in the south deal with it all the time. Do you have to re-work the loads once hunting weather or cooler-cold conditions come around ?

Yes .Warm weather if your powders unstable will yield questionable results but it will let you know your max load fairly quickly

 

[D-4297]

Be a really happy camper if I got to shoot in a high of 85-90F . Shot some load work-up at BA today and it was only 107 . That load should work "DOWN" to around 75F before it has to be adjusted Up a little . We all have our crosses to bear ... Seriously ; Start with about 75 to 80% of a "Book" load , and dial it in from there . Your HOT temp range is my nice fall day temp and a 90-95% load that works at 85 might be over the edge at 95F in your climate . Nothin wrong with bein cautious . I have a load I shoot in my winter temps , 40's to 60's , I won't even chamber above 95 degrees .

 

[Zero333]

For hunting big game your load will be good.

I've worked up loads in the hot summer and hunted with them in the winter and only had to adjust my zero. If the loads opened up any I couldn't tell and it wouldn't of been enough to miss.

 

[INTJ]

Several years ago (1999) a fellow named Stan Watson (OKShooter on a couple forums) did an extensive test with temperature and powders. He was a professional ballistics consultant for the Army. He tested some powders in a pair of 30-06s, a pre 64 M-70 and a Rem 700 with an Oehler PBL statin gauge/chrono. He found that the temp resistant powder he tested did indeed have less variation in pressure that standard powders.

See the pic for a summary. Please note that it’s propellant temperature that is the issue, not outside air temperature. Also, the only sure way to know is to test for yourself.

With LR BR it is never an issue because you always check and adjust your load prior to each match. With little BR it is not an issue because you are loading at the match and adjusting for micro conditions.

For hunting, I always use temperature resistant powders. While no powder is 100% unaffected by temperature, the ones designed that way do seem to have an advantage. I have been able to work up loads in 100 degree weather and then shoot them in the 30s with no meaningful difference in velocity. I was using cartridges that were in the 300 WSM to 338 RUM range, and I think larger cases may be less sensitive to variations than smaller cases. I also always choose the lower node in a hunting rifle.

 

[Texas10]

I worked up a 308 load back in April, which for here in Central Texas was unusually cool due to a lot of rain. The best load was 43.0 grs of Varget and 168 gr SMK. Shot literal one hole groups at 100 yds out of my Shilen Select Match bull barrel, with the high temps for the day still in the 70's.

Lately however, it wasn't performing so well, so I loaded up an abbreviated OCW and shot it at 210 yds yesterday. Starting at 42.6 grs I shot a .4 moa, 5 shot group, while 42.8 shot a .8 moa, 43.0 shot a .9 moa, and 43.2 shot a .3 moa group. The temp was 98 F and light rain was falling occasionally.

While none of that really matters with a hunting load, I was a bit surprised to see a Varget based load vary so much from the temperature as it is one of the least temp sensitive propellants available. But then I'd seen the same thing with my 223 load and Varget, having dropped the charge at bit to keep it shooting well in Texas Summer temps.

 

[Ned Ludd]

My experience with the effect of temperature on load development is that it is much worse when a load is worked up in cooler temperatures (i.e. ~50-55 degrees F or less), and then used in much warmer temperatures (i.e. > 80-85 degrees F). Loads I've worked up during the warmer months seem to shoot reasonably well in the late fall through early spring, whereas loads worked up when it was fairly cool seem to fall apart during the hot summer months and have to be adjusted to avoid over-pressure and accuracy/precision issues.

I really have no good explanation why this should happen. Nonetheless, re-working a load developed in cooler temps to adjust it for warmer weather is usually not too difficult. I find that dropping the charge weight to bring the muzzle velocity back down to what it was in the cooler temperatures usually brings everything back in line.

 

[INTJ]

I worked up a 308 load back in April, which for here in Central Texas was unusually cool due to a lot of rain. The best load was 43.0 grs of Varget and 168 gr SMK. Shot literal one hole groups at 100 yds out of my Shilen Select Match bull barrel, with the high temps for the day still in the 70's.

Lately however, it wasn't performing so well, so I loaded up an abbreviated OCW and shot it at 210 yds yesterday. Starting at 42.6 grs I shot a .4 moa, 5 shot group, while 42.8 shot a .8 moa, 43.0 shot a .9 moa, and 43.2 shot a .3 moa group. The temp was 98 F and light rain was falling occasionally.

While none of that really matters with a hunting load, I was a bit surprised to see a Varget based load vary so much from the temperature as it is one of the least temp sensitive propellants available. But then I'd seen the same thing with my 223 load and Varget, having dropped the charge at bit to keep it shooting well in Texas Summer temps.

If you didn’t record velocities you don’t know for sure that it was temperature that was causing the issue. There are several other factors that can cause what you are describing.

 

[Metal God]

I'd say if you're working up a load in the heat and may later use it in cold weather there is less danger involved for pressure spikes so you should be gtg there . You tend to get pressure spikes if you are shooting in hotter weather then you worked the load up in , also if you are at max pressures in the lower temps you can really get high pressure spikes shooting that same load in hotter weather .

The only way to know if accuracy is going to be an issue is actually testing the load in cool temps . Some put there ammo in a cooler for a short time to lower the temp of the ammo then test it to see what difference there may be . In that case though your barrel will still be hotter then the ammo so not sure how that would effect results . When I'm testing specific match loads I record the ambient temp outside and the barrel temp before shooting each charge . There is rarely a 10* variance from outside temp and my bore temp when I start each charge . How ever if you put your ammo in a cooler and get it to say 40* but your barrel is 80* . That is not going to give you an accurate representation as if you were shooting in 40* temps because in later case your barrel would be closer to 40* as well .

You will almost certainly have a POI shift which is easily corrected with a quick range trip and a new zero .

 

[Stepsjframe]

When we lived in the northern mid west, our club held matches all year around.
It could be as hot as the tropics in the summer and with snow and ice winters.
The loads could be very different with changes in the weather.
Sometimes the ammo would be chronographed for major and minor.
Loads from summer might very well fail to make the required power factor in winter.