At What Temperature is Load Testing Safe?

J

jackstrawIII

New member
I've spent the winter developing test loads for several of my guns. I started at the listed minimum and increased in 0.5 or 1.0 grain increments (depending on the acceptable ranger for each cartridge) up to the listed book max. So now I have a bunch of loads I'll shoot, select which powder charge gives the best accuracy, then load up a bunch of rounds with that powder weight for hunting/target shooting later in the year.

With that said, I know I need to be on the lookout for pressure signs as I work my way up in charge weight. I've read that cold temperatures can lower the pressure of the charge. My concern is, if I test my loads now when it's 20 or so degrees F outside, I could end up selecting a load that's fine now, but generates too much pressure when I use it later in the summer or early autumn.

Here's my question: at what temperature is it ok for me to start shooting these test loads without worrying about pressure due to temperature increase later in the year? 30 degrees? 40? 50? Sunny and 75?

Here is a list of the the calibers I've loaded, and what powder was used:
223 - Varget
308 - Varget
270 - H1000
6.5x55 - H1000
358 - Ramshot TAC

I've heard that the Hodgdon Extreme powders (Varget and H1000) are "less" temperature sensitive? Does that factor into all this?

Thanks in advance.
 
First of all just because you have a listed Max load it doesn't mean that you need to go to it. You should have been checking perhaps 3 rounds then go up and load another 3 rounds... You could easily find that max is not safe in your rifle... as you inspect the cases. And then have to take the hot (in safe) loads apart.

As far as what temp. goes. All though I am not a chemist and have not tested for temps. I feel confident enough that I can tell you to watch the extreme hot temps like laying the cases in the hot summer sun for long periods of time. We have some new super powders out there now that clime to be in sensitive to temps but don't push it.

I'm sure some one out there can give more details.
 
I do the majority of my load work ups during the summer. It's not too unusual to be at the bench at 100+*F and putting up with long waits for the barrel to cool down some. Pays to do loads for several rifles. I generally try and do four and make a day of it.
Ok so the whys and wherefores? Simple, if high pressure is gonna show up, it's during that time of year. Any top load I work up will be safe come hunting season. Some of the powders I use, Winchester's WMR (long discontinued BTW) is one I have a decent supply and when shot at the range at Raton New Mexico just before my elk hunt, when temps run from +30F to pushing zero, I have found that it hasn't made much difference in point of impact, at least from my rifles. :confused: It does make me question temp sensitivity. Any load work I do this time of year will be double tested again come the hot months to insure they don't give too high pressures.
Paul B.
 
I will limit my comment to your use of H1000 in the 270 Winchester: According to my 2005 Hodgdon manual, the maximum load for 130, 140, and 150 grain bullets, are all compressed loads with that powder. the 130 grain load shows somewhat low pressure. I don't believe you can get enough of that powder in the case to damage your 270. If you stopped at maximum charge, you should be entirely safe, WITH THAT POWDER, IN THAT CALIBER.
 
Here's my question: at what temperature is it ok for me to start shooting these test loads without worrying about pressure due to temperature increase later in the year? 30 degrees? 40? 50? Sunny and 75?
Click to expand...

I like Friar Frog's rules of Internal Ballistics:


A (Very) Short Course in Internal Ballistics

Fr. Frog's Rules of Internal Ballistics
1) There ain't no magic powders!
2) There are no magic cartridge cases!
3) Details! It's in the details.
4) Inconsequential increments are meaningless.
5) Most gun writers are pathological liars.

http://www.frfrogspad.com/intballi.htm

I have developed loads in all temperature ranges, shooting over a chronograph , recording velocities, recording temperatures, looking for the gross signs of pressure, and nothing to date is a perfect predictor of future performance. What inevitably has happened, is that the loads I developed to book velocities at 75 F weather conditions, I have had to cut after having pressure issues in rifle matches above 75 F. This is even more true for loads developed in high 40's or low 50's F weather. My chronograph cuts out when temperatures are in the low 40's. Things go a lot worse in 90 F. And this is even with the so called extreme powders. Most of my issues have been with H4895, which is an outstanding powder. But being an "extreme" powder has not meant that higher temperature and match conditions will not lead to hard extraction.

I can say, colder conditions bring very little pressure problems, but once temperatures go up, and the rate of fire goes up, you will experience things.

I am going to say, pressure is not your friend. If you can do the same job at a lower pressure, your life will be less frustrating. Things go bad faster at higher pressure. I have had and will continue to have more and more problems with maximum loads. They are so frustrating. No problems at the bench, problems at the matches. Argh.

This is more of a philosophical idea, but how much velocity do you need?. I recently tested my first production year M70 Winchester in 30-06. I bedded the action, free floated the barrel. I cranked out some standard loads that I have used before in my 30-06 match rifle. That rifle has a Wilson 26" match barrel. Velocities in that rifle for the same loads are above 2600 fps with a 175 grain bullet. Which, by most shooter's standards, is slow. So are the velocities I recorded in this rifle, which are below 2600 fps with a 175 grain bullet, unacceptable?


Code: 
[SIZE="3"]1937 mfgr 30-06 Winchester M70 24" barrel,  		
								
								
148  Israeli FMJBT 59.5 grs WC852 IMI cases CCI 200			
								
23-Jan-17	T = 59 °F							
								
Ave Vel =	2658	 						
Std Dev =	27							
ES =	76	 						
Low =	2628							
High =	2704							
N =	10			 				
								
								
175 SMK 48.0 grs AA4064, wtd, lot 2398 Czech, TW54 CCI #34 OAL 3.30" 		
								
23-Jan-17	T = 59 °F							
								
Ave Vel =	2590	 						
Std Dev =	30							
ES =	97	 						
Low =	2551							
High =	2648							
N =	10			 				
								
			
								
175 SMK 48.0 grs IMR4064 wtd, lot E89AU, 1989 powder,  TW54 CCI #34 OAL 3.30" 	
								
23-Jan-17	T = 60 °F							
								
Ave Vel =	2563	 			 	 		
Std Dev =	27				 			
ES =	92	 						
Low =	2525							
High =	2617		
N=        10	[/SIZE]

Even though I would like the 175 grain bullet to be going at 2650 fps, I don't think a 175 grain traveling at 2563 fps is going to bounce off the hide of any animal hit with it. So, really, how much velocity do you need?. Velocity goals set the amount of pressure stress you are going to create on your cartridge case and rifle. I believe the pressures I am experiencing with these loads is likely to be 45,000 psia, based on a SWAG of the velocities. At these pressures, I don't believe I am going to have pressure problems when things get hotter, especially as these are well characterized loads in other rifles. When is enough, enough?

I would recommend sticking to mid range loads if you are developing loads in cold weather, but, if you want to really know how they will perform in hot weather, there is absolutely no substitute for shooting them in hot weather.
 
Read the above information for an answer to your problem. I'm constantly amazed at the amount of information on this forum and the lengths folk are willing to go to make that information available.

I'm just posting with an anecdote from a gun writer showing op has a valid question.

The gun writer developed a varmint load in the winter and one summer day he grabbed is rifle from the rifle rack in his pickup truck, where it was very hot and took a shot at a coyote. He didn't hit the coyote and didn't see where the round hit and the coyote didn't act like a bullet had just whizzed by so he took another shot, same results. He found out the velocity had increased to where the jacketed bullet was coming apart when fired.

So the question is a good one.
 
In the days when the sun never set on the British Empire, Eley and Kynoch would provide "tropical loads" for the sportsman going on safari or shikari in the tropical summer.

Modern powders like Hodgdon Extreme and IMR Enduron are said to be less temperature sensitive. But powder "burn" is a chemical reaction and is bound to be at least somewhat affected by temperature.

I would not take winter maximums out in the summer.
 
JackstrawIII,

If you used loads from a manual, the top loads in most of the current manuals have been pressure tested in SAAMI standard conditions of 70±10°F. They recommend conditioning reference ammunition at 70±2°F and 60±5% RH for 24 hours before firing, and I suspect most folks with controlled testing areas just keep them that way all the time, but don't know it first hand. The critical chamber dimensions of the test gun will be SAAMI minimum specs with a plus 0.0005 inch tolerance. For all the loads you mention, the barrel length of that gun will have been 24±0.010 inches.

Given the above, these same loads are likely to be low in cold temperatures, particularly for cold barrel shots. Denton Bramwell showed barrel temperature matters more than ammo temperature to actual pressures, so later shots will come closer to warm weather pressure.

So, what could go wrong for you? Three things:

  1. You have a load near to one showing pressure signs in cold temperatures, so you can expect you'll have to lower it in warmer temperatures.

  2. Due to differences in barrel time, the load most accurate in the cold may not be the most accurate in warm temperatures.

  3. If your house is very dry in winter and the powder gets very dry, the burn rate will increase. Norma's load manual has details on this. It takes about a year for water to equilibrate in loaded rounds, so you'd need to let the ammo sit that long in more humidity to clear that up. How much difference it makes depends on your humidity. Burn rate can increase as much as 12% going from 80% RH to near 0% RH in the desert. If it is in the range of 40-60% you should be OK.

What can you do about it?

When you shoot to test summer loads in the cold wear an ammo belt under your coat so it stays warm. Fire a couple of fouling shots to warm the gun up, then reach into your coat for each round as you load. Keep up a rate of fire that doesn't let the gun cool too long between shots, and this will be closer to warm weather shooting as far as pressure and barrel time go.
 
Uncle Nick almost always says everything you need to know, not that other folks don't have great info and experience.
I'll try to only mention a few things. Ime Some of the reloader powders have velocity differences of 100-150 fps between hot and cold days. And the observed pressure differences are are extreme. I use a lot of the extreme powders, varget, retumbo, h100, h4831 and ar comp.I usually load to pressures where I'm satisfied with the velocity and accuracy and I can still get ten or more firings with neck sized brass, usually norma. All powders, even the extreme series react differently to the very hot days. Eric Lang, a ballistic guru drew out a graph for me when I had a similar question. It showed the pressure v.s. temperature and that even the extreme powders showed significant increase after 70F. As uncle Nick mentioned the testing near 70F that seems to be a benchmark for most powders before pressures start to climb quickly. I suppose this post already plenty of info but I hope this helps a little bit.

Sent from my SM-N920V using Tapatalk
 
Oh, we should mention that the new IMR Enduron line of powders are temperature compensated, too, giving you more options in that regard.
 
Short version. As long as you're under 100 degrees I think you'll be OK, especially with the Varget loads. Assuming you didn't exceed the max load in the load manual. Most book loads are calculated at around 70 degrees. Most powder will vary 1-2 fps per degree of temp change. Varget and most of the temperature stable powders are only changing velocity about 1/2 fps per degree.

It is something I consider. Here in GA 105-110 degrees at the range during summer time is common and upper 90's aren't unusual in early deer season. Ammo left in a vehicle could be over 140 degrees.
 
Those powders probably won't be terribly sensitive to temperature in those applications; but you never know.
Last summer, there was a discussion here about a Varget load that a member found perfectly safe and sane during the winter, but blew primers in the summer.



The only way to know is to test.
Like many things in reloading, every load is unique. There's no way of truly predicting what's going to happen until the trigger is pulled. We can make fairly safe assumptions, based on experience and boatloads of professional and amateur testing


Some thoughts:

In my own experience with temperature sensitivity and testing...
I've tested half a dozen cartridges from well below freezing, on up to about 105 F, specifically seeking temperature insensitive loads. All hunting loads get tested in cold, moderate, and hot weather; since I hunt from the heat of summer (coyotes, varmints, and antelope), to the depths of winter (late season elk, cougar, bunnies, etc.), and nearly any rifle can be used for nearly any of that game.

Some powders are tame and predictable, with only minor variation.
Some powders are quite volatile and much more unpredictable than 'experts' would have you believe.
And some powders don't do what they're "supposed to".
Every load is unique, and they don't always play by the rules.


In my own development and testing of my "one load to rule them all" .270 Win load (it took several years), all powders that should have been "temperature insensitive" turned out to be too erratic with even just 30-50 degree temperature changes (even if superbly predictable and consistent within a narrow temperature window). Yet, the best powder to come out of my testing was RL-19, a powder that every one of the 'experts' had singled out as being the "most temperature sensitive" in my list and some had flat-out told me it would never work across the ~100 degree temperature range I was looking at. :rolleyes:

That doesn't mean that RL-19 is not temperature sensitive, though. It just means that my particular bullet, case, case prep, sizing method, primer, rifle, chamber, powder charge, seating depth, and powder combination showed extreme consistency and temperature insensitivity.

As for temperature...

My testing of the .270 load started at about 40 F (late winter), went up through 98+ F (mild summer), back down to below freezing (next winter), and then over the roller coaster again, down to almost 0 F and back up until I maxed out at 105 F (two summers later).
Generally, the initial test increments were roughly 20 degrees apart.
Most other temperature testing has been done under similar conditions (often starting in mid to late winter, and going on from there).


One of the best tools to use to see how temperature is influencing the load, is a chronograph.
You'll see increased, decreased, or erratic velocities long before you see pressure signs. (Unless running right on the ragged edge, to begin with.)


As mentioned, don't leave ammunition in the sun (even in the winter), and don't leave it in a closed vehicle unless it is thermally protected. -- I use 50 cal ammo cans, but wrap them in a towel, coat, or blanket in warmer weather. It works fairly well to insulate and stabilize.
 
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