Sighting in during hot weather then hunting in cold?

[MichelD]

If I sight in this week for example at 24 degrees Celsius and then shoot at game in October at 10 degrees C or colder will my POI be different?

This is with 270, 280, 7x57 or 300 Winchester magnum if it make a diff.

[Fred1]

Not enough to matter hunting. I know I cant hold a rifle (or bench one) that well where temperature would make any difference to my POI. But if you are one of those guys shooting dimes at 100 yards in competition it might make a difference.

[Weatherby Fan]

If I sight in this week for example at 24 degrees Celsius and then shoot at game in October at 10 degrees C or colder will my POI be different?

This is with 270, 280, 7x57 or 300 Winchester magnum if it make a diff.

In theory yes as the air is thinner when hotter and thicker when cold so POI would/could change slightly, but as Fred says hardly enough to worry about in hunting situations, I've never worried about it.
Most animals are shot inside of 200 yards so not worth worrying about IMHO

[Swissrallyman]

You will have muzzle velocity differences, if sighting in when its hot and hunting in the cold will reduce your muzzle velocity. If you have a chrony you can check yourself. If you develop a load in the cold and its near max pressure you could get dangerous pressure spikes in the heat. Some of the extreme powders are not supposed to be temperature sensitive enough to make a difference but better safe than sorry. I remember testing 308 reloads und let some of the rounds heat up in the sun on the hood of my truck until they were quite hot...instant 100fps muzzle velocity increase and cratored primers. That was with a semi mild target load.

But if you are shooting factory ammo I wouldnt worry just confirm your point of impact before you go hunting in the cold.

[Busterpayton54]

Short range doesn't matter hunting wise really but I've found up to 14fps per degree centigrade with what was supposedly a temperature stable powder, so you've not only external ballistics to deal with but also internal.

Now if you are signing in at 30c, and might see some 400 yard shots in -30c, well it might be worth assessing.

Just for fun I punched this into my ballistic program, .300 win mag, federal blue box at 2960fps muzzle, 100yard 0, temp 100f, 300yards you 14" and the 500yard drop is 60.5".

Simply changed the temp to 0f and at 300y you have 17" and 500y you get 74" drop.

That is not even taking powder sensitivity into account. Also this is assuming the rifle stayed at a 100yard 0.

Oh oh and then you get into barrel harmonics, where it may end up hitting higher than predicted.

Final result, it might be good enough but you never know until the bullet hits something.

[Lastcar]

Just getting started with reloading. When developing a load how does one decide what temps to test those loads?

The obvious answer seems the same temps you'd expect to normally shoot, or take the most important shots. I.e. hunting season temps.

Seems heat of the summer is a poor time to develop a load?

[bearheart]

Shoot year round, keep a notebook, it's fun, educational, all the cool kids are doing it! Temp will make a differnce the further you shoot. Also if you reload, some powders are temperature sensitive.I try to stay away from them.

[BgBlkDg]

No, the opposite is true in that IF your handload does not show excessive pressures at 85*F, then it is more likely to be safe and reliable at usual hunting temps. I prefer to work up loads, as I am currently doing, at the hottest part of the year and then load in bulk during the post-Christmas period until about May.

Now, be AWARE that many contemporary rifles will NOT show "traditional pressure signs" when the actual pressures are approaching the 70,000 psi level where cartridge brass begins to "flow" and cases may rupture. This, is due to various factors in manufacturing and it thus becomes even more useful to have and USE a properly set up chronograph.

When, you get to the top velocity given in PRESSURE TESTED data, as in the Nosler No. 7 and 8 manuals, STOP THERE. I can go into exhaustive detail on this, but, am too sore tonight to sit here much longer.

Where Michel's query is concerned, I would never worry about this as temp. swings only make a difference in very long range shooting and the cartridges he refers to with contemporary powders will all be close enough in BC hunting season temps. so that the concern is groundless. How, many actually hunt at -20 or even 0*F, so, check your scope at the place you hunt and call it good.

[tigrr]

What powder? Your asking a too general of a question. Some powders as mentioned are temperature sensitive. Some are not.

[Alfonz]

Just getting started with reloading. When developing a load how does one decide what temps to test those loads?

The obvious answer seems the same temps you'd expect to normally shoot, or take the most important shots. I.e. hunting season temps.

Seems heat of the summer is a poor time to develop a load?

Bingo! That's how I would go about it.

[Lastcar]

What powder? Your asking a too general of a question. Some powders as mentioned are temperature sensitive. Some are not.

Depending on the caliber and various loads in the manuals:

H4831SC
H4831
IMR4350
Varget
Super Performance
Hybrid 100V

I'll look into them and see which seem to be more sensitive to temps.

Sounds like there is lots of live and learn ahead. "Live" being key. Or at least not get seriously hurt.

Certainly going into it cautious and careful. Starting with the minimum and will work my way up from there.

Starting tomorrow night. Looking forward to a new aspect of shooting and learning something new.

[Shooter Jr.]

Varget is pretty temperature stable. most double base, extruded powders are. I've recently gone to load development with IMR 8208XBR in hopes of some consistent MV's.

[MichelD]

OP here.

I'm using H4350 in the 7x57

Federal factory loads in the 270 and 280

H4831 in the 300 WM

[tigrr]

A little experiment is in order. Take 4 rounds and put them in the freezer. Put them in a cooler with ice packs and go to the range. Shoot them at a target, over a crony would be good.
Shoot 4 rounds out of your warm pocket over a crony. Aim at the same dot on the target and see if there is a change in point of impact. Compare crony numbers.
I have seen a difference of 30 feet per second in rounds fired in summer and winter but it meant little in hunting rounds.

[tigrr]

H4350 is actually quite stable. 5fps spread
H4831 is less stable. 25 fps spread.
My 270 likes IMR 4064 and it is 5fps spread.

[brian]

Realistically if you sight in now then you should put a few downrange before you go hunting on the 10th just to make sure you are still zerod in and everything is working right. That'll both answer your question and make sure you are good to go.

[Fred1]

Holy crap! You guys are great! Oh the science... Now how am I going to shut all that out of my head when im trying to shoot!?!?! I can over think a shot bad enough without reading all this. geez...... Pretty interesting stuff though!