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I thought that a thread concerning load development and ambient temperature might be in order now.

Being that it is now mid-January, and most of us who shoot are somewhat cooped up, now is the time that much load development takes place amongst our ranks.  This is a natural way to beat the cabin fever we seem to endure each winter, especially if you live in the snow belt.

However, this tendency to develop a pet load during the winter months can and does have potential dangers!  Although we don't hear much about it any more from gun writers, the hazards still exist.  What am I talking about?

The hazards of working up a maximum load in any cartridge during winter months when the ambient temperature can be a full 50-60 degrees below temperatures encountered later in the year when the same ammo can and will be used!  A load that is worked up to absolute max during the winter, and all range testing and chronographing is done when the temperatures are near or below freezing, can and most likely be into the <span style='color:red'>red zone</span> once temperatures become comfortable for shirt sleeves!

I once worked up an absolute max load in my Marlin .375 Winchester using a BTB .377"-250g LFNGC bullet and a mighty stiff load of AA 1680, and fire-formed .30-30 brass.  That load, worked up one very cold week in December yielded 2360 fps with only slightly pushing the pressure envelope!  I was ectatic!  It was superbly accurate and repeated loading and firing of the same case revealed good case life.  I was in fat city!

Now, for the rest of the story.  Our fall black bear season began on a very hot September 15th that year.  Using my wonder load in the little Marlin .375 Winchester, I was loaded for bear.   I had an opportunity to take a coyote about noon that day, the temperature, while not having a thermometer handy, must have been near 80 degrees, I had been comfortable in a T shirt since before sun-up that day.

When I popped (at) the coyote, my world momentarily went black!  My shoulder cried out, and my right hand was wrenched open as the lever on the rifle sprung open!  I staggered backwards, and after recovering from the shock of surprise, assessed the situation.  I had missed the coyote from about fifty yards... I don't have a clue where that bullet went, but it must have left in the form of smoke and lead vapor!  The cartridge case remained stuck until I got home, removed the lever and the bolt from the rifle and drove it out from the muzzle with a brass rod!  The case had a huge hole where a primer once had been!

I double checked the loads left in that lot of ammo, it had all been loaded in the same session, with the same lot of brass, the same powder measure with an unchanged setting, primers out of the same box and bullets from the same lot.   After pulling the bullets from every fifth round and checking the powder charges, all was as recorded on the loading label.

Now, for the stupid part... I figured that something must have been wrong with the one load I fired.  It was the next day with early afternoon temperatures near 90 degrees.  I tested one more round out of the Marlin... again, pain, sprung action and a bullet with unknown destination.  Again, back to the shop to pull lever and bolt and drive out the case with a brass rod... with the same results as the round fired the previous day.

Although this is absolutely the most extreme case of this I have experienced, it was a sobering event, and it prompted me to make detailed notes not only of pressures but temperatures during those testing periods. (If you will notice our Printable Resources Loading Notes and Targets all have spaces for temperature)

Yes, we now have powders that minimize this pressure swing due to temperatures.  The new Hodgdon Xtreme powder series does minimize, but not eliminate this phenomenon.  I have noted over the years since my described experience significant changes not only in velocity but pressures as temperatures have fluctuated.

Back in the heydays of Ivory Hunting in Africa, the Kynoch ammo loaded for use specifically on the Dark Continent was loaded to pressure levels such that with the extreme heat of African exposure, pressures would not spike beyond the designated accepted standards.

We too can learn a lesson here.   Enjoy the winter load development sessions... but <span style='color:blue'>PLEASE</span> don't seek that magic MAX load with MAX pressures and MAX velocities!  Otherwise you might find yourself <span style='color:red'>MAXED OUT!</span>

I'm somewhat concerned about some of the loading data that people are sharing that has been recently developed, as although they may very well be within the realm of reasonable pressures now, in the winter conditions they have tested them, I suspect that some very serious pressure problems are on the horizon as ambient temperatures rise.

Use caution, enjoy the winter months, and keep GOOD records.

God bless,

Marshall
 

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Been there, done that! I was working up a hot load for my .357 Mag with WW 231 and a Rem 125gr SJHP. I was trying to achieve1450 fps. I don't remember the exact load I used but my GP-100 shot that load very well and cases popped right out of the cylinder. Of course it did, it was WINTER! I thought ....great, I'll just go ahead and load up a 1000 rounds and be done with it. That summer I spent many a nights with my new friend...The Kinetic Bullet Puller. I had to pound those rounds out of the cylinder with a hammer. STUPID!!!
Now I test in the summer and shoot in the winter.

God Bless

Chris
 

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Thank you for reminding us of this. I read a magazine test of just this very thing and loaded factory ammo was chronographed and pressure tested at varying temp from freezing to extreme desert heat. The results were surprising in the extreme spread of both velocity and pressure. One of the tests was a very realistic test of several cartriges left on the dash of a vehicle in hot sunlight for several hours, The cartridges were very hot to the touch and were way over factory pressure limits when fired. If your velocity is way over what it should be, chances your pressure limits are too.
 

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.

An example of what can happen when a load is developed in January and fired in August. Sitting in a hot pick-up for several hours didn't help, either.




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Hope that was the extent of the losses....

This is why I do most of my load work in mid April or May, most of the time these temps are pretty close to what we have during hunting season. THen I play with them right on through the summer. Even if it DOES eventually get cold I would rather sweat it out working up the load and know it's fine in the heat rather than the other way around.
 

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I know it is temping and rewarding to wring out a high velocity load with max accuracy. I always preferred to keep loads moderate for caliber. It is often easier to get better accuracy when a load isn't being pushed to the max. If I need more power out my rifle, I get a bigger caliber. I hand load for both economy and the accuracy challenge. I have seen a barrel obstruction blow up a gun with serious injury and I had a Mosberg 12ga bolt gun fire a shell before the shell was half way in the chamber. lucky I was still holding the shotgun at just above waist height. Top half of the shell blew off and it all came right up into my face. That would have cost me an eye had I not been wearing glasses. I though I was going to be permanently deaf. I was incoherent and deaf for about 10 min or so. I am more than a little wary now of pressure problems or malfunctioning guns.
 
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