Temp Sensative Powders

[BearNaked]

For the people that use temperature sensitive powders, do you adjust your charges to the temp of the day you are shooting? I have a load that is salty at the 70-90 degree temperature but once it goes above 100 then it opens up. The higher the temp, the more pressure which equals more speed which is now out of the optimum range. I am sure it will change once temps drop below 40 but here in south texas that will only last for like 2 weeks.

For the trolls:
Yes I can change to a powder that is not as temp sensitive. still not the question.
I use a certain powder for the velocity and groups I get with it.
Yes it could be me having an off day but still not the question.

 

[JMGlasgow]

I usually find a load that works well for average temps in my area. I also look for pressure signs when hot and back off if needed.

If I have to back off down to the next accuracy node then so be it.

 

[spife7980]

The only thing that I use temp sensative powders in are hunting rifles and I dont really worry that much if it opens up to an inch on the hot days or the few freeze days we get. Thats with something like 4064. Rl15 or something double base or really sensitive might be another story and is exactly why I dont use the double base powders, Im scared of them.

 

[NFAJohn]

I am sure it will change once temps drop below 40 but here in south texas

I’m in Houston and RL22 is my powder of choice in 4 different rifles I load for. I do my load development in the summer time and just rock on. I stacked it deep when I built my 300WM and see no real reason to change powders as my load is lights out in my 300 and 7stw.

As far as adjusting the data for when I’m shooting I just input the velocity at different temps into my kestrel and let it spit out firing solutions.

 

[steve123]

Heck, I add or subtract a 10th or two on insensitive powders depending upon the time of year it is.

The worst example I experienced with temp sensitive powders was AA2520. 125fps from a summer day to a winter morning. I thought my scope was broke, lol.

I used to use R17 quite a bit and it wasn't too bad. I changed over before I got to experiment much with it. Spring to fall it averaged a 40 fps swing.

 

[OLD308]

I’m in DFW area and have never had the accurate load be over pressured in the summer. But I don’t chase velocity. From 223, 308, 6.5, 7mm, and 300 win all have the same effect. If your chasing velocity over accurately your situation could be the norm. Hope this helps.

 

[BearNaked]

I have been running rl17 and on the super hot days, it opens up to an inch. If its a normal day then it is shooting a solid 1/2" groups.

I was just curious if anyone ever messed with the charge due to weather. Mostly for long range shooting. I'm not worried about a 1" group at 100 yards on anything but once you reach out there, that starts to grow a lot more than I would like.

 

[XLR308]

The majority of the cartridges I use temp sensitive powders in are fairly small cases 223, 68spc and I use quite a bit of H335, 1200R but I generally work up to max or near in above 90° temps. I haven't noticed any great differences in accuracy for hunting but I haven't used them in freezing temps either.
That was when I lived and hunted in South and central Texas and central Arkansas now I am in Colorado so that approach I don't think would apply.

 

[Subwrx300]

I have been running rl17 and on the super hot days, it opens up to an inch. If its a normal day then it is shooting a solid 1/2" groups.

I was just curious if anyone ever messed with the charge due to weather. Mostly for long range shooting. I'm not worried about a 1" group at 100 yards on anything but once you reach out there, that starts to grow a lot more than I would like.

Like @XLR308, I have a small caliber 224V that I use CFE 223 with due to reliably precision. However it is temp sensitive (about .6-.7fps per deg) and I've got three loads at .1 intervals to use for different temp ranges:

25.0 = 65-90+ (summer shooting)
25.1 = 50-80 (transition shooting)
25.2 = <32 - 60 (winter/transition)

Target velocity is 2,740. 25.2 grains at 115 deg shot 2788 and at 32 deg it shot 2711. Each .1 changes velocity about 20-25fps but temps will drop/increase velocity by about the same. It was an easy test to run to find good calibration factor, but you need to have good Chrono data and temp over time to be sure. I put 10 rounds into ice filled cooler, 10 normal rounds in empty cooler (65-70deg), and 10 rounds on my dashboard for 2 hours (115 deg in direct sun). Shot two 5 round strings each with 2 min between over Chrono to find temp sensitivity factor. Then loaded .2 intervals for ladder test from 25-25.8 to get velocity per charge graph.

I'm fine shooting within a -+20fps range throughout the day: for longest targets, might need one extra click in morning, perfect though lunch and one less click at hottest part of the day. No big deal. Wind will kick my ass long before .25moa elevation change and most targets seem to be more forgiving vertically than horizontal.

 

[mcfred]

I agree with SubWRX above. Run the numbers, collect data and plan accordingly.

On a .223 I use in the local matches with ball powder, I collected velocity data when it was 'cool' and use that data and load all the time. A water bottle (cool or warm as necessary) and some insulation in the pack stabilizes temps well enough to stay on target for several hours at the club matches where I routinely see up to 35˚F temp swings. That works fine unless it's some extended winter camping/hunting trip where everything freezes. Then just collect data for effing cold and use that. IMO 40 FPS isn't going to make a difference for hunting inside 400yds with 'modern' cartridges.

 

[Subwrx300]

For reference, here is a picture of POI at same ammo at 75 deg 2740fps (top), 32deg 2711fps(middle) and 115deg 2788fps (bottom). All shot at 300 yards in 80deg air temp. The two shots in hot ammo we're JUSSSTT off the target to left about 1/4" (holes in plywood backer). Top right bullet of top group was sighter (and fouler). Dots are 1".