Temp sensitivity

[Mikecr]

While my guns will group well with various temps, none would be LR accurate over a 50deg window.
I don't know where GG got his data, or if it's valid, but the ~80deg line he mentioned is real.
Loads do seem to shift there.

It's implied that this is a bad thing(because of pressure jumps), but the truth is it's an advantage -provided you load developed above 80, and disciplined to use the barrel only within this tuned range.
After all, it's a relatively narrow range.
If I needed to, I would do the same for hunting below ~40degs, another line, where primer ignition (w/resp to capacity) shifts.

For long range shooting, there is no way I would use a single gun for a range of 40-90degs.

 

[Bart B]

For long range shooting, there is no way I would use a single gun for a range of 40-90degs.

Two of the barrels used on my .30-.338's were fired in competition in temperatures from the upper 20's (Raton, NM, early March) to high 90's (Port Clinton, OH, late July). Both held the same load of IMR4350 and RWS 5341 primers to under 3/4 MOA at 1000. Wish I'd been able to put 'em on paper that well in the cold weather when 'twas hard to hold still shivvering like jello in an earthquake.

I've had similar experience with .308's over almost the same ambient temperature range and observed no significant difference in accuracy through 1000 yards. But the zero will change; cold air's thick and cold powder's weak so the lower muzzle velocity means more drop. Hot air has the opposite effect. Such is life.

 

[azmetalman]

Check out this information from Hodgon.

http://www.hodgdon.com/smokeless/extreme/page3.php#top

azsugarbear hit the nail on the head. AZ is a land of extremes both in temperature and elevation. When temps reach 90 deg. I put my selected loads in a small lunch cooler with a couple of blue ice packs or frozen water bottles when I head for the range. I put a couple of layers of bath towel material between the cartridges and the ice packs. I take out 1 cartridge at a time and only when the barrel/action has cooled to my liking. This has worked well for me. I won't test loads when temps reach 100+.
This means shooting very early and not for very long during the summer. For what it is worth it works for me. RL22 and H4831sc are my mainstays for powder in the .270 and 30 cals. Always remember that what works for one rifle may not hold true in another or at least to the same degree.

 

[X-man]

You also need to consider what chamber the powder is going in.
In my 300Win rifles I get better accuracy with Rl-22 and have not found it to be twitchy. I do not shoot in 120 degree weather either so keep that in mind.

If I have my facts right the military uses H1000 in the 190SMk load?

 

[Bart B]

If I have my facts right the military uses H1000 in the 190SMk load?

In the .300 Win. Mag. ammo loaded by the USN's Crane Ammo Depot for sniper use I broke down had Reloader 19 powder in it and confirmed by talking with them.

I doubt any slower powder would give the consistant accuracy it does. IMR4350 under 190's and 200's HPMK bullets was the favorite back when the .300 Winnie was popular for long range prone matches.

 

[BrentM]

Interesting thread. One day I went out and pounded a rock at 800 yards. I had no vertical movement in the entire string. All landed with in.5 MOA. I would have to guess from chamber to fire each round was in for 30 seconds to 1 minute. I did take a break from the 1st 4 rounds and went down to check the results. Came back and shot the next 4. The barrel on this rifle gets a little warm after 6 consequetive shots so I like to give it a rest after 4.

I use retumbo which should be stable like 4831 and 4350 by Hogdon.

 

[Bart B]

Brent, if your barrel's a good one and properly fit to the receiver, your should be able to start with a cold barrel then shoot 30 to 40 shots 20 to 30 seconds apart and not see more than about 1/4 MOA rise in bullet impact at 800 yards. If it won't do that, something's wrong; probably the way it was fit to the receiver face; a common problem.

 

[BrentM]

Well I don't know much about anything really but this rifle seems to be solid. I have shot it from 10 degrees to 55 from 800-1500 and it always hits dead on with my shooter ap solutions. I have turned the powder temp section off and just shoot it. My un-scientific approach to temp stability for a hunting load. LOL. I am super happy I don't have to worry about 1 more thing affecting down range performance. My goodness I have enough stuff trying to destroy POI and powder temperature issue's would make me wanna cry.

 

[TOM H]

Brent, if your barrel's a good one and properly fit to the receiver, your should be able to start with a cold barrel then shoot 30 to 40 shots 20 to 30 seconds apart and not see more than about 1/4 MOA rise in bullet impact at 800 yards. If it won't do that, something's wrong; probably the way it was fit to the receiver face; a common problem.

I've been reading your post and just what barrel contour are you talking about. Also the test you talk about breaking down sniper ammo for the 300mag was that done thru the military and why was it done?

 

[Greyfox]

I doubt a 25 to 75 degree F change in powder temperature would shoot bullets close enough to the same muzzle velocity to have the same drop at 1000 yards with the same ambient temperature for both the bullet goes through. Note cold air has more density than hot air, so a bullet leaving at the same speed in each will drop more in the cold air than the hot air. And the 25 to 75 degree F powder temperature used in the same air temperature will end up with more drop at 1000 yards with the colder powder. If air and powder temperature were the same, the cold powder in cold air would cause even more bullet drop; less energy plus more dense air equals more bullet drop.

I think you are referring to my post. The shooting that I spoke of at different temperatures from 25-75 are at different locations and therefore corrected for changes in air density and temperature using my ballistic computer. Under those circumstances my impact points are on at 1000 yards at each location. I do confirm my 200 yard zero
which is usually on. When checking velocities at my home location in the Northeast, I have measured velocities at this location and they're very close from 25-75 degrees. This location is the initial conditions that are loaded into my ballistic program. The Retumbo load I use works across this range in my 6.5x284 and I'm now finding similar results in my 300WM. My rifle and powder are usually all at the temperature I'm shooting. I don't know about all the various effects of temperature, but using this approach my rifle is close enough out to 1000 yards to hit the vitals of several deer at the different locations and temperatures I hunt.

 

[Bart B]

I've been reading your post and just what barrel contour are you talking about. Also the test you talk about breaking down sniper ammo for the 300mag was that done thru the military and why was it done?

The barrel contours I'm referring to that held zero after several shots in succession were five different ones used in accuracy testing. They all held 1000 yard zeros within 1/4 MOA for at least 30 shots fired in less than 20 miinutes.

First three .30-.338 Win Mag barrels, 1.2" at the receiver, .9" at the muzzle, 28 inches long. One Douglas, one Obermeyer and one Kreiger. Win. 70 post '64 action with face squared to barrel tenon axis, squared bolt face and lapped lugs.

Fourth, a cut off and rechambered 30" Palma .308 Win. barrel (with about 2800 rounds through it) retapered to 1.2" at the receiver, 1" out about 3 inches past the reinforce then to .7" at the muzzle; total length 26 inches. New chamber was a .300 Win. Mag. Same action type and truing the bolt and receiver face up and lapped lugs.

Fifth barrel was a 30" Kreiger medium Palma taper fit to a single shot Paramount action with squared up receiver and bolt faces and lapped locking lugs. Only 20 shots were fired in under 10 minutes into 3.2 inches at 800 yards.

Ten or so .308 Win. barrels made by Hart and the military armory in Springfield, MA, were shot at 600 through 1000 yards with all sorts of ammo. Up to 25 or 26 shots would be fired in about 20 minutes and no stringing of shots happened in the matches they were shot in. Same for those other barrels above used for testing that were shot in many matches and they never changed point of impact while they heated up. I've seen more than a few folks shooting M1's and M14's in special rapid fire matches putting 24 rounds into a 600 yard target in 50 seconds; 1 foot groups or thereabouts which is pretty good considering precice sight alignment and picture are not attained. Those barrels were the hottest I've ever touched or fired myself.

The .300 Win Mag ammo was USN issued stuff given to me that I broke down to measure bullet release force and weigh the powder charge. I had called Crane, Indiana, ammo depot and asked them what powder was in the ammo by its lot number.

 

[TOM H]

The barrel contours I'm referring to that held zero after several shots in succession were five different ones used in accuracy testing. They all held 1000 yard zeros within 1/4 MOA for at least 30 shots fired in less than 20 miinutes.

First three .30-.338 Win Mag barrels, 1.2" at the receiver, .9" at the muzzle, 28 inches long. One Douglas, one Obermeyer and one Kreiger. Win. 70 post '64 action with face squared to barrel tenon axis, squared bolt face and lapped lugs.

Fourth, a cut off and rechambered 30" Palma .308 Win. barrel (with about 2800 rounds through it) retapered to 1.2" at the receiver, 1" out about 3 inches past the reinforce then to .7" at the muzzle; total length 26 inches. New chamber was a .300 Win. Mag. Same action type and truing the bolt and receiver face up and lapped lugs.

Fifth barrel was a 30" Kreiger medium Palma taper fit to a single shot Paramount action with squared up receiver and bolt faces and lapped locking lugs. Only 20 shots were fired in under 10 minutes into 3.2 inches at 800 yards.

Ten or so .308 Win. barrels made by Hart and the military armory in Springfield, MA, were shot at 600 through 1000 yards with all sorts of ammo. Up to 25 or 26 shots would be fired in about 20 minutes and no stringing of shots happened in the matches they were shot in. Same for those other barrels above used for testing that were shot in many matches and they never changed point of impact while they heated up. I've seen more than a few folks shooting M1's and M14's in special rapid fire matches putting 24 rounds into a 600 yard target in 50 seconds; 1 foot groups or thereabouts which is pretty good considering precice sight alignment and picture are not attained. Those barrels were the hottest I've ever touched or fired myself.

The .300 Win Mag ammo was USN issued stuff given to me that I broke down to measure bullet release force and weigh the powder charge. I had called Crane, Indiana, ammo depot and asked them what powder was in the ammo by its lot number.

So these barrels are not hunting barrels or nothing to do with long range hunting or any type hunting? I don't see any hard in telling us what these rifles were used for.

 

[Bart B]

So these barrels are not hunting barrels or nothing to do with long range hunting or any type hunting? I don't see any hard in telling us what these rifles were used for.

No, most were not. One started out as a Palma rifle barrel then ended up as a long range hunting one in .300 Win Mag.

Barrels don't know how they're being used nor what they're aimed at. Every one will behave the same way in any shooting discipline; they're just like bullets, cases, powder and primers.

 

[MNbogboy]

I find this post very interesting..
The OPs idea his first post of averaging chrono results
is pretty much what a lot of us do when developing loads at different temps..
Bart B was spot on when mentioned about chamber time and the thermal co-efficients of brass & powder...
Everyone will see big differences from time to time especially with warm temps...
Big mistake everybody makes sooner or later is to leave your live ammo out in the sun...
That brass "sucks" up heat from the sun fast, faster than the powder inside warms up by far..
Just a minute or two in the sun and the chrono usually shows it as a fast one and sometimes a beginner will blame the powder...
One theory is; with the "hot" brass, the heat transfer during the combustion is slowed and more energy is left to push the bullet..This is makes some sense and agrees with Newton..
Can we calculate and predict exactly how much?...
Probably not unless we had a lot more information including all the barrel dynamics including the dimensional/tempural changes a barrel makes as energy is applied from its external & internal enviroments..
But we can use our range data or even set up tests to get a better handle on it...
I often mark in my notes of extra chamber time with an individual shot..
These "usually" show extra velocity and sometimes I eliminate these from SD calcs...
This is "usually" depending on where the barrel is in its warm up cycle.
Personally I shoot all year long from below zero temps to 90 above and have never worried about powder temp sensitivity.
There are many more things you can try to control that will have a bigger effect on your results..
My opinion/advise is to collect your data in detail as you work up loads.
If you can not reach your goal over a wide range of temps with one powder or charge you may have to change powder or compromise velocity, but you can get there.
With all the data you collect you will be able to adjust for and shoot well with any conditions.
Randy