Temperature sensitivity?

[Stape]

Was reading through some posts yesterday and had read someone mention that they will not use 748 during the summer, or something to that effect. This got me thinking, because I use a lot of 748. How sensitive is it to temps, and what are those temps? I'm not going to be concerned about unsafe conditions exist at 100 degrees if you leave your ammo sitting in the sun, on an iron skillet, in your black driveway, in Arizona, but would like to hear of any adverse conditions in real word scenarios, like sitting in a range bag or ammo can on a hot summer day ect.

I would imagine there could be a velocity increase, and thus change your POI. I rarely load to the upper edges in the data, it just never provides me with the most accurate ammo, so why waste the powder.

Just curious on others takes on this. Living in NE and other very moderate climates, its never been an issue that anyone had addressed, but now I live in MO, and summers here get F'n hot.

 

[EddieCoyle]

I think it's overplayed.

Within microseconds of the primer igniting, the inside of the case is going to be a 3500-degree inferno. I don't think a few degrees either way at the start is going to change things all that much.

On the other hand, warm humid air is less dense than cold dry air, so I would expect rounds to hit lower (especially at long ranges) in the winter.

 

[eisenhow]

I don't know anything about 748 and rifle powders, but have some experience with some pistol powders. A few powders are reverse temperature sensitive including WST. If you ride too close to the edge with your PF you could find yourself shooting minor instead of major and for no-score instead of minor. Ask a banned NES member/attorney about a very hot Area 7 Championship he shot Open-Minor with his Limited-Major gun.



I think as long as your not near max or shooting over a chrono you'd never know.

 

[mac1911]

Best to just try some loads. Work up a load for the summer , then save 10 rounds and see how the shoot come next Jan when it's 4'F ......now you need to wonder if any change is you freezing your ass off or your ammo. Also you rifle maybe weather sensitive also. I have a M1 garand that will shoot around 4moa in the winter months but once june/july comes it will not hold a group. I figure it's a stock issue and humidity plays a role.

 

[cockpitbob]

The only time I've seen temperature matter is when shooting very long range 600y+ where slight variations in muzzle velocity start to show in noticeable changes in bullet drop. And you have to be real accurate in other respects (<1MOA) to notice the difference.

 

[jpm]

as eisenhow said, I think its only really a factor if you're on the edge of max loads

 

[Steve Marshall]

Absolutely there is a difference. However the difference is relatively minor. You would have to be at the extremely ragged edge at -30 degrees, use the same load at +100 degrees e.g. to slightly affect pressures and trajectory. The various extreme powders are attempting to solve a real yet minor problem. They are evolution rather than revolution. Most of the differences with these powders are usually size of kernels and deterrent coatings, relatively minor changes to effect minor improvements. Remember the "superperformance" loads from Hornady? I think it was. They refused to divulge what powder and the proprietary loading techniques. The improvement was usually on the order of 150 FPS or so in rifle hunting calibers. Back aways there was some Super powder from Vitahouri? ( 3n37? ) that gave an extra 100 FPS with .357 over the norm. Then there was short cut powders. They changed the formula for Unique and so it goes.

 

[NavelOfficer]

When it's extremely cold outside, I do much less shooting. That is temperature sensitivity to me!

 

[Stape]

Thanks for the input. I got crazy on the Dillon and loaded thousands of .223, granted my load is proven in my rifles and I've used it for years. I've never shot this load in super hot summer conditions and some of my ranges here are open cover where ammo might be sitting in the sun.

 

[NavelOfficer]

Yes indeed! Brass can get quite hot in direct sunlight. Just take advantage of "El Sol" when decapping your GP-11 brass...

 

[RKG]

I have observed a MV Delta, very small (on the order of 1%) between rounds fired at 40°F and rounds fired at 80+°F. Might be a concern of a benchrester, or maybe someone loading at the absolute max, but not for the rest of us.

I've used Win748 for a long time, in 5.56, .243, .308, .30-06, .30-30, and probably half a dozen other rounds, with nary a problem.