W760 temperature sensitivity question

[Chilly807]

That's exactly the point I was making, my moderate 243 loads were still safe but considerably faster in hot weather than when they were developed, in early spring.
If they'd been on the hot end of the scale, they'd be even hotter in summer weather.
As Bad Bob said earlier, there are less sensitive powders that work well, so why deal with W760 if you don't have to? I've got about half a pound of H414 left that'll just sit on the shelf in case I can't get anything else at some point.

 

[bearhunter]

In fact this is my main concern, I'm loading right now for moose next month but what if i'm shooting for training next summer.....

Larry

If you're loading now, for next month, you will be fine then and next spring without any concerns.

I've taken velocity checks on H414/W760 at -40C, +25C and +35C. The load was developed at +25C.

The rifle used was a 7x57 98 Mauser, with 139 grain Hornady SSTIL.

Load - 51grn W760 over CCI250 magnum primers.

This load generates 2850 fps average out of a 24 inch barrel, safely on a 98 Mauser, may not be safe in an older model action.

Velocity at 25C = 2850 fps.

Velocity at -40C = 2780 fps.

Velocity at +35C = 2890 fps.

I have large, blended lots of W760 and H414 so I don't worry about lot to lot variances.

Depending on how fast or slow your particular lot of powder is, there may be a minute difference. Likely you're purchasing canister grade propellants so the difference may not even be noticeable. Canister grade powder factory controls are so close these days that most folks don't even bother to check the lot numbers or notice a difference in the accuracy of their ammo.

I'm a tad anal on such things, simply because it used to be something that had to be watched closely. It's also the reason I started blending all lots of the "same powder type designation."

 

['Boo]

The worst pressure excursion I have had was using a supposedly temperature insensitive powder - H4350

I had some 300 WSM loads worked up at ~16-18 degrees Celsius that were wonderfully accurate. As luck would have it just before the season opened temperatures were in the upper 20's . When I went to the range to confirm zero before the season started the first round blew the primer out of the case.

After running a bunch of the so-called temperature insensitive powders out of a dozen different cartridges over several season I suspect most so-called improvements in powders are wishful thinking at best.

 

[huntingfamily]

I was using W760 in my 7x57 model 70 for a while. Good powder for velocity and accuracy but I found it is definitely temp sensitive.
Switched over to H4350 and it has been better in that regard.