Accuracy lost on warmer weather

[FrogFire7]

I'd be curious if you loaded to the same velocity you were shooting in the winter, if the loads would shoot the same

 

[Joe-boy]

This interesting topic has come to a conclusion of not really having a conclusion. I once tried shooting cold and warm cartridges one after another and they grouped pretty much similarly. Also it seems that the accuracy at 150 meters is significantly worse than 100 meters. I've also shot terrible groups at colder weather since, so it looks like there is something a bit mysterious happening here and it's not just the ambient temperature that is playing tricks here.

My best guess is that this was a case of being on the edge of a node and poor stability of 53 gr vmax in a 1/12" rifling. I've since switched to 50 grain vmax which seems to be behaving a bit more consistently.

 

[Mike Matteson]

Well it's going to be over 115 degrees today . Yes it may be 65 degrees difference so let's say the change is 1.5 FPS per degree in temperature rise……. That will be 96.5 feet per second and if your at the threshold or upper limit of the charge and pressure let alone accuracy then the cooler is a good idea.

Sorry being so lone getting back. Part of it is that your max load and are hot loads to start with. In Mexico-North I worked up a load for my 308NM a great many years ago in the winter there. (if you want to call a winter) Weather changed about 50 degree between times. I had a 165gr Nosler at 3400fps and excellent grouping in the winter time. It got to be in the early summer or June, and The first one round down the tube that that type of powder load, just to see if anything had changed. I below a primer out of my case and had a hell-of-time getting my bolt open. One thing for sure I hadn't done any checking on how powders reacted to temp. A close friend with me that day brought that up. I took 49 out of 50 cases apart back at home. Changed to H4350 and lost a 100fps, but never had a problem after that. I hunt in weather from -20 to 110+.
Both times I had work my load up to about 5grs above the max shown on any reloading manual. I know that hot and I load that way in all my rifes. I do work up loads to achieve that those increase powder loads. That was the first time I ever when about the reloading manual callout. I stop at or below creatoring the primer. Lord help me if I am showing ejector marks on the case. I stop before getting there. Now I do run ups on my powder loads of anywhere from between .25grs to .5 grs in single loads to just watch for how my primer are reacting to the different powder loads. I combine that in ladder test now.
A 30fps variation is about 8.5" @ 1000yds. A 50fps variation would change your bullet by as much as 14" @ 1000yds. So tell me where you want to be at.
I Learned a lot here over the past few years.