Tuning loads for cold weather?

[LongBomber]

Been playing with the labradar and some test loads in my 260ai and 6.5cm in the cold.
I developed a load for the 260ai in the summer around 65 deg. 129LRAB and RL17 in Lapua brass, ran a ladder from 44.6 up to 46.6, hit two nodes, the low node was wider so went with the middle (44.8gr) and did a seating depth test. Running 3044fps, with an ES under 20 for 25 shots in the summer temps and very good accuracy.
Was out last weekend plinking at my gongs, 28'F temps. Running a speed of 2995fps, still good es and accuracy. But a loss of basically 50fps.
Played with a small ladder today at the same freezing temps. 44.5-44.9 in 0.1 steps, speeds were 2993 to 3008 fps. Was only shooting at 100y but the group was about 1/3moa for the 5 shots.

Now my question is, would you move up a few tenths in powder charge to hit the summer speeds and test to see if that load is still in tune? Or accept the lower speed?

 

[Tex LR]

My preference has always been to prioritize accuracy over velocity. If your happy with the group size, I would not worry about 50fps unless you like the dial in process and have the time / materials.

 

[The Oregonian]

Been playing with the labradar and some test loads in my 260ai and 6.5cm in the cold.
I developed a load for the 260ai in the summer around 65 deg. 129LRAB and RL17 in Lapua brass, ran a ladder from 44.6 up to 46.6, hit two nodes, the low node was wider so went with the middle (44.8gr) and did a seating depth test. Running 3044fps, with an ES under 20 for 25 shots in the summer temps and very good accuracy.
Was out last weekend plinking at my gongs, 28'F temps. Running a speed of 2995fps, still good es and accuracy. But a loss of basically 50fps.
Played with a small ladder today at the same freezing temps. 44.5-44.9 in 0.1 steps, speeds were 2993 to 3008 fps. Was only shooting at 100y but the group was about 1/3moa for the 5 shots.

Now my question is, would you move up a few tenths in powder charge to hit the summer speeds and test to see if that load is still in tune? Or accept the lower speed?

I agree with the above poster on accuracy over velocity. I would check to see where you are in the node, however. That is, if you are still in your sweet spot but now on the edge of it, you may want to move back to the middle. If you hunt in weather 30 degrees colder, will that take you below your accuracy window?

So I would test loads a few tenths below where you are and also to the upper edge of your summer mode to see how things perform. I would let that dictate whether or not I adjusted anything for your go to load.

In other words, just make sure you have an accuracy window on either side rather than trying to squeeze 50 fps out of it. I am a self taught reloader and load developer but that is my $.02.

 

[Mikecr]

Sounds like you did a great job with your load development and testing so far.
I wouldn't change a thing

 

[LongBomber]

Velocity wise I am now below the node, but the ES and accuracy is still hanging in there.

I might have to do some testing to see if the accuracy falls apart at longer ranges, and maybe test with some increased charges. It looks like 0.8gr should get me back up to the speed of the node from the summer.

 

[Mikecr]

If the loads are for hunting, then don't forget that this needs to be COLD BORE ACCURACY to hold meaning. That is, not hot bore grouping.

 

[Greyfox]

Been playing with the labradar and some test loads in my 260ai and 6.5cm in the cold.
I developed a load for the 260ai in the summer around 65 deg. 129LRAB and RL17 in Lapua brass, ran a ladder from 44.6 up to 46.6, hit two nodes, the low node was wider so went with the middle (44.8gr) and did a seating depth test. Running 3044fps, with an ES under 20 for 25 shots in the summer temps and very good accuracy.
Was out last weekend plinking at my gongs, 28'F temps. Running a speed of 2995fps, still good es and accuracy. But a loss of basically 50fps.
Played with a small ladder today at the same freezing temps. 44.5-44.9 in 0.1 steps, speeds were 2993 to 3008 fps. Was only shooting at 100y but the group was about 1/3moa for the 5 shots.

Now my question is, would you move up a few tenths in powder charge to hit the summer speeds and test to see if that load is still in tune? Or accept the lower speed?

IMO, I think you have a couple of options. The first, if your velocity/temperature curve is consistent, and your ES and accuracy holds, you can leave your load alone and program this the curve in your ballistic calculator (at least in the AB App.) to account for this change. According to your results shown you are loosing approximately 1.3FPS per 1 degree of temperature change. This is pretty close to the reported temperature stability of R17. While it's certainly an option, if you change your charge weight to accommodate velocity, you may have to chase it at various tempertures between the extremes.
Another option would be to try a different powder that could provide better temperature stability. For example, H4350, with a similar burn rate delivers .16FPS/degree. I have found this powder to deliver this level of stability at the temperature extremes in my 6.5x47 and 6.5CM.
See the chart below:

 

[Benny338]

IMO, I think you have a couple of options. The first, if your velocity/temperature curve is consistent, and your ES and accuracy holds, you can leave your load alone and program this the curve in your ballistic calculator (at least in the AB App.) to account for this change. According to your results shown you are loosing approximately 1.3FPS per 1 degree of temperature change. This is pretty close to the reported temperature stability of R17. While it's certainly an option, if you change your charge weight to accommodate velocity, you may have to chase it at various tempertures between the extremes.
Another option would be to try a different powder that could provide better temperature stability. For example, H4350, with a similar burn rate delivers .16FPS/degree. I have found this powder to deliver this level of stability at the temperature extremes in my 6.5x47 and 6.5CM.
See the chart below:
View attachment 114210

Agreed 100%. Change powders or calculate for temp. If you start doing different charges to always make the speed the same it will get even more confusing and you will always be trying to take certain loads for certain weather.

 

[Trnelson]

I've been down that rabbit hole with WC867 years ago. Trying to use different charges to maintain a velocity window as temperatures changed. It was a larger change in velocity as temperatures changed. My load would fall out of the accuracy window if it was too cold or worse yet spike into unsafe pressures if it was too warm. The same load that shot 3,220 at 30• would stick the bolt and blow the primer right out of the case if you tried to fire it at 90•. That was an embarrassing mistake that I was fortunate enough to get through with just a trip to the gunsmith and not the emergency room.
I had loads worked up for every 10• change with a temperature written on the case, worse yet I had to carry a selection of them while I hunted and try to plan ahead as to what I would need to have.
Eventually, as better powders entered the market I went to them. Looking back it seems crazy, but it's what a lot of us did some variation of to maintain suitable accuracy.