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temp stability of powder

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Unread 07-20-2010, 01:57 PM
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Re: temp stability of powder

My testing resulted in IMR4350 being more stable than H4350..
But that was before Hogdon got their hands on IMR!
I don't know about newer lots.
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Unread 07-21-2010, 12:27 AM
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Re: temp stability of powder

Originally Posted by Boss Hoss View Post
I tried the ice chest thing as well and found that the tests are not valid. Brass heats up Way Too Fast. Need to test in ambient conditions to get valid results but if it makes you feel better then fine.

Try it and you will see. I have done the testing on my competition guns and while the velocity variations are not as large as WMR (yes WMR is old but I have a lot of it and it performs in the mid size magnum cases) or RL 22 for example it is still present.

Example is H4350 for my 6.5x284 ---- with 49.3 grains and a 142 SMK (sorted by actual bearing surface with the Buhay gauge to eliminate any variable) the difference is avg of 2895 at 45 and at 85 2965. At 1K that is ugly unless you compensate for it which I do. These loads have a spread of less than 15 fps at 45 and 10 fps at 85 which is acceptable. Have done this on my sporters to a lesser degree as the shorter ranges the difference is not enough to worry about.

Specifically what results are you getting?

I freeze loaded cartridges overnight in a 0 degree freezer. I then transfer them to the range in a cooler( also frozen ) packed with Rubbermaid Blue Ice. Do they warm a little? Maybe but very little. I then shoot the frozen rounds first, usually two 3 shot groups at a time. I pull them from the cooler one at a time. I shoot these fast as not to have the rounds heat up in the chamber or as little as possible. I am shooting for data not groups. I let the barrel completely cool then repeat until I feel I am getting good data to analyze. This is usually 15-18 rounds. I then let barrel cool again, clean bore and then start with rounds that are not frozen and follow the same process. The outside temperature for these tests vary but I try to do it in the 80-90 degree range. Any warmer does not make any sense since I don't hunt big game in 80 degree plus weather. I work with a high and low only and average from there. Varmint rounds are all developed/finalized in 90+ degree weather since it is what temps I wiould be shooting in. From High to low I lose anywhere from 20 to 55 fps. depending on the load with Extreme powders. Yes 55 is a lot at longer ranges but I have seen 150-200 fps. differences with non Extreme powders. The only exception is a .243 Win load with H4895 and 55 grain BT that had a variation of 240 fps. I still have not figured out that one. I ALWAYS look to try and find a fault with a load. For example, if I shoot a real good group with a certain recipe in testing I will test that one recipe extensively before calling it good. I look for something bad. This process works for me. I have used it in everything from 17 fireball to 35 Whelen. I use it with all powders because Extreme powders are not always the most accurate but I try the Extreme first. With some powders I have a warm weather and a cold weather load. Is this an absolute scientific test? No, as there would need to be multiple barrels/twists/lengths/primers and even brass combinations that would need to be tested, plus even maybe freezing the rifle to make all things equal. But it works for me.
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Unread 07-21-2010, 03:59 AM
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Re: temp stability of powder

I notice a huge difference in H 414 when above freezing. Every 20 or so degrees would result in velocity increase and loss in accuracy.

I shot H 414 all winter with 190gr SPBT in my 30-06 and had no problems with accuracy, about 1moa at 400 yards in 40 degree temperature swings all below freezing. As soon as it got warmer I had to change to IMR 4831 so I didn't need 4 different loads standing by to use according to temperature.

I noticed that IMR 4064 was temp sensitive using 110gr bullets in my 30-30. I was shooting about 12 inches higher at 300 yards every 10 degree temperature change. When I moved up in bullet weight to 150grs it became much more stable. Testing was done between 50 and 80 degrees.

I changed powder to VIHT N 135 with the 110gr bullets and that works wonderfully. I only have tested those from 50 to 90 degrees so far.
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Unread 07-21-2010, 12:38 PM
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Re: temp stability of powder

I believe that temp sensitivity is affected by several variables. The bigger and fuller the case - the more pronounced any weakness with a powder becomes. I also believe that temp sensitivity can vary depending on the temp range itself. For example, RL22 may not exhibit much temp sensitivity when comparing between 32 degress and 60 degrees. But may begin to show bigger swings when comparing between 60 degrees and 90 degrees.

This is, in fact, what I found to be the case with RL22 & RL19 when I was reloading for my 300 RUM. In the end, I used H1000.

A couple more thoughts: It's easy to talk absolutes when basing them on our own experiences. But therein lies the danger. What works in VA may not work well in CA. Here in AZ, most bench rest shooters shy away from VV powders because they just don't perform as well as others in AZ competitions. But they all have several pounds of VV on hand when they go to shoot on the road, because it does shoot well in NM. Go figure.

Secondly, we all refer to air temp and forget that surface temp may be more important. This is a factor in states where the sun shines a lot - like out west. Remember hearing someone say that the temp was xxx "in the shade"? That may have a lot to do with what is actually happening with your rifle. Although you may be hunting at 70 degrees air temp, the temp inside your action/magazine is probably a lot higher. When shooting outdoors, I have noticed that after 8 AM in the summer, my barrel never cools back down. In fact, the barrel temp continues to get hotter the longer I leave it exposed to the sun.

In Phoenix they did a study a few years ago utilizing a laser temp reader - like the ones they use to check the temp of AC air coming out of vents too high to reach. While the air temp in Phoenix was 112 degrees that day, the sidewalk was closer to 130 degrees. A dark colored metal seat at a bus stop was 150 degrees; and the metal lid of a galvanized trash can was 180 degrees.

Just some more food for thought.
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Unread 07-21-2010, 05:54 PM
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Re: temp stability of powder

My testing was no more scientific than mentioned, and I'm sure that results represent a whole pile of factors combining in the abstract. With this, I give no credence to Hodgdon's 'Extreme' stability hype.. And they provide no more basis for their claims than I might to the contrary.

What I do know is that it absolutely cannot be predicted that Hodgdon's will be more temperature stable than any other. Only local testing would show it or not. Same with VVs powder..
Yet often it is implied as a psuedo-fact that mere use of 'extreme' powders alleviates the issue.

Not that I have a problem with Hodgdon. Hell, I think I have plenty of their whole line.
I focus on best results first in my choice of powder/brand. Mostly because, I'm not big in group shooting, but cold bore accuracy instead.
For this, keeping rounds in my pants pocket has worked well both at the range and in the field -regardless of temps. I do it as a habit now, always, including load development(cold bore).
Also, my guns are all single shot, loaded just prior to pulling the trigger.
So I figure my ammo is within ~10deg of body temp, and it has performed well there.

When I tested H4350-vs-IMR4350, it was for a 1K grouping gun, and of course I can't fire off 10rnds into a group without ammo potentially changing in temps, because I wouldn't be pulling them each from my pocket..

Good discussion
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Unread 09-02-2013, 08:52 PM
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Re: temp stability of powder

This is an old thread, and I am resurrecting it as some things were not discussed. I shoot in extreme temperature variations, both environmental and the temperature of the rifle, and thus the ammo. Central Montana is one of the worst places on Earth to shoot at long range if accuracy is the issue.....and long range shooting is the norm here. You CAN jump a whitetail in willow thickets by streams in nearby mountains....but that is NOT where the big mule deer are found.

Temperature sensitivity at ANY environmental temperature can be checked by firing a long string of shots at 1 minute intervals and checking the velocity with a chronograph. Immediately after firing a shot, place the next round in the chamber to let it "cook". The absolute worst temperature stability I have experienced is with IMR 3031 where with a 10-string shot I started with moderate .223 Rem velocity and ended the string with high end 5.56mm NATO velocities. FPE was well into the 1300's of foot pounds at the end. Every single shot had a higher velocity than the previous shot. This is practicaly unheard of with a temp stable powder.

Ball powder is not always as temp sensitive as some may claim. The military ball rounds I stockpiled were both made by FNM in 5.56mm and 7.62mm NATO, in the standard 62 grain and 147 grain bullet weights. Both use small ball powders and both show almost no velocity variation when doing long strings of shots. Velocity variations from shot to shot are due to the unequal powder charges, which are always thrown instead of individually weighed in military standard issue ammo. Bullet weight varies a couple of grains also. By about 4-5 grains if it is .308 cal 147 grain and supplied by Winchester. However, average velocity stays fairly constant with temperature variation in FNM military ammo. These are better performers than their domestic LC and WCC competition.

Hodgdon Extreme powders do rather well here, and I am converting many loads over to those powders. Ramshot is another powder line that has gotten my attention. Being Belgian, I would expect some of the Ramshot powders to be what was used in my FNM military surplus ammo. Ramshot TAC is especially noteworthy in .223 Rem applications. Especially if you want to throw charges without weighing them for volume shooting aplications such as prairie dogs.

H4895 and Varget often beat all other contenders in .223 Rem and .308 Win for me, with one offering slightly better accuracy while the other offers slightly better velocity, depending on bullet weight. I have yet to see any pronounced temperature sensitivity with either powder when firing long strings of shots. The downside is that charges must be individually weighed as neither one meters well. I generally choose a powder that gives a slightly compressed charge, as this provides consistency in "lightup" with no chance of "flashover" as well as giving no variation if the shot is angled up, down or level. I never shoot loads that fill the case below 90% capacity. 80% capacity can have a higher peak pressure than a compressed load, even if the velocity is low. Compressed stick powders generally give the lowest extreme spreads in velocity. I like to hear the "crunch of quality"when seating a bullet.

I have worked up too many loads at one temperature to have it shoot much worse at a widely different temperature. The Ultimate Sniper Manual says to change your zero with every 20 degree Fahrenheit change in temp and every 1000 foot change in elevation. You can't do anything about the change in air density with altitude variation. However, with the right powder AND load density, the 20 degree Fahrenheit rule does not necessarily apply. Notice I said LOAD DENSITY. A powder that in temp stable will STILL show velocity variation if the case is underfilled and you shoot up, down, or level. It has a different "lightup" in each situation, and that has NOTHING to do with temperature stability. Get ALL your ducks in a row before looking at temp stability only. Slight compression of powder, especially stick powder, seems to add stability to a load. A Lee factory crimp has also become standard, as bullets that are merely pushed into place will have different release forces depending how long the rounds have sat around. When pulling bullets that have been loaded for a long time, I can feel the "pop" as the metals shear apart. A round that was loaded yesterday will have a much lower release force and no "pop". A Lee factory crimp adds a more consistent release force as the presence or absence of metal bonding over time is swamped out by the factory crimp.
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Unread 09-02-2013, 09:11 PM
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Re: temp stability of powder

I have tested H4350 in my 284 win in 73-103 degree temps. My load has an es of 2 fps over four shots, according to the magnetospeed, done twice in the same conditions on the same day. This was done in 73 degree ambient air temperature, with the ammo and gun at the same temp. I then tested the exact same load in 103 degree ambient air temps with the ammo and gun at the same temp. There was a 5 fps change in average velocity over 5 shots with es staying at 2. Sd was 1.5 fps. Accuracy remained the same .5 MOA.

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