Powder Temperature Sensitivity

[GeauxTide]

Had a discussion that got me thinking more about this subject. I've been going to and fro on Varget and H4895 in my 308 bolt guns. 4895 has given a SD of 7 on a particular load. I've been using 4895 since the 70s in 308 and 30-06, hunting in temps down in the 20s and I've not had any issues. In the Battle of the Bulge and the Chosin Reservior campaign in Korea, temperatures were Zero to -30F. The M-1 Garand and the Browning 30 Machine operated fine on the 4895 powder loaded in the 30-06 cartridge.

I was visiting with a target shooter who tells me that I'm going to have trouble with CFE223 in my 6.5 Grendel, recommending XBR-8208. I'm not a target shooter, so I'm not worried about my .2" groups going to .5 or 1" in colder weather. I haven't chrono tested in cold weather, but will do so. I would appreciate any thoughts.

[Bart B.]

Contact the powder company asking what you should expect at various cold temperatures.

[old roper]

This may help.

https://www.hodgdon.com/extreme-rifle-powders/

[GeauxTide]

Thanks, wasn't aware that H4895 was an extreme powder.

[Unclenick]

Yep. It's a tad faster than IMR 4895. If you look at Hodgdon's data, you find the maximum loads of H4895 in the .308 Win and the .30-06 are all around 2 to 4 grains lighter than the IMR 4895 maximums.

As to temperature stability, this is a process to do with deterrent coatings and it has to be tailored to particular bullet and cartridge combinations for maximum effect. In some other combinations, it can have no clear effect at all. Also, most velocity variation is caused by a warm barrel heating the primer up. The powder's contribution is small, so you may not detect the difference between a compensated and an uncompensated powder outside of where your first cold barrel shot will go. For hunting, that matters a lot. For target shooting with sighters, it doesn't matter at all.

This article has some good information on the subject.

[hounddawg]

I have not used anything except XBR 8208 in my AR Grendel so I can't speak of other powders but the XBR gets me 1 MOA'ish results with a mid priced upper and 120 gn SMK's. Word at the range was to be careful at the top end of the recipe with 8208, supposedly it can spike pretty fast if you try and push the envelope. I never saw any problems shooting it in 90 and 95 degree temps but then I stayed under the max recommended charge by a few tenths. I lost interest in the rifle and never fine tuned the load. I do have a couple of hundred Barnes TSX's with which to develop a hunting load. That is one of those to do list kind of things for me at the moment. Let us know how the CFE .223 works for you

[Metal god]

I was visiting with a target shooter who tells me that I'm going to have trouble with CFE223 in my 6.5 Grendel, recommending XBR-8208. I'm not a target shooter, so I'm not worried about my .2" groups going to .5 or 1" in colder weather. I haven't chrono tested in cold weather, but will do so. I would appreciate any thoughts

I agree that CFE 223 is not a good choice if you’re going to have large temperature swings .

[Don Fischer]

Just my opinion but over the years I have read a lot about this problem of temp sensitive powder's. I'm not sure how much of it is true other than to say that it does make sense to some degree. Say you develop a load in 50* weather, how much change in temp does it take to actually make any meaningful difference?

[Unclenick]

The temperature compensator in QuickLOAD for an IMR4895 load in 308 Winchester that produces 60,000 psi at 50°F (10°C), will produce 62,131 psi at 68°F (20°C), so an increase of +18°F (+10°C) increased pressure about 3.55%. Going up another 18°F (10°C) to 86°F (30°C) increased the pressure by almost the same percentage, to about 64,240 psi. I tried going from 70 to 88 with W748 and got an increase of 3.6% and change. So the numbers are all in that range for non-temperature stabilized powders.

In most instances, the change won't take you from a reasonable pressure to proof pressure, but it can change enough to take a tuned load off its sweet spot.

[old roper]

Living here in Co @ 7700ft and yesterday it didn't get much above 42 and if I was going to range 8/9 this morning it be mid 30. Lot hit range on days like this to check zero.

Unit's I hunt DOW has rifle range and it open May thru Nov and get real busy non resident/resident during hunting season check zero.

[RC20]

The actual firing of a gun (Bulge/Chosin) has almost nothing to do with powder (assume its good powder) and vastly in those conditions with how they lubed the gun (or left them dry probably)

It has nothing to do with what temp stability is about. The powder was chosen (no pun intended) to work in extreme conditions. Temp stability type is less variation than its older counterpart powder, its still there, supposedly less though some test have shown that is not true across a -40 to 120 degree comparisons.

The velocity variation in combat are a non issue. Even more so in the human wave attacks ala Chosin.

As Artillery is the main killer even a variation enough to cause a miss (and at what range) is not a major factor either. Allies once they got un-confused has outstanding artillery (and tank) support including the VTF fused artillery shells that were released (actually radar shells that did an much more effective air burst).

Both battles had solid air support.

[Bart B.]

Centerfire rifle ammo shoots bullets faster as the powder heats up from hot barrels. Rounds need to fire within 15 seconds of chambering. Or come down a click on the sight every 20 to 30 seconds of powder cooking time. Come back up to zero as barrel heats up. Run tests with your ammo to see what's best.

People at the Camp Perry nationals have blown a chance to win or break a 1000 yard record due to hot powder. A boat in the impact area caused a check fire. Two minutes later when the range was safe and firing resumed, the next shot for score struck the 9 ring at high noon. The hot powder shot the bullet faster.

[Jim Watson]

Elmer Keith knew that. When he had a miss called at Camp Perry and hadn't fired, he took the round out of the rifle and set it in the end of the cartridge block to cool.

Powder "burn" is a chemical reaction and is inherently affected by temperature.
I would like to see an explanation of the "reverse temperature sensitivity" reported for some Ball powders, it does not fit the physical chemistry.

[Unclenick]

I've never seen reverse sensitivity claimed for any of it. It is possible someone got a load hot enough that it moved the bullet barrel time to a phase of barrel bending that caused the bullet to exit low and print low on the target, so they thought they had reverse sensitivity.

[old roper]

Bart, don't you get sighter and total time for all is 50 mins

[Unclenick]

Different matches have different time rules. For Palma, you get 22 minutes for all sighters and 15 record shots on a target. For 600-yard Slow Fire in the National Match Course, you get 1 minute per shot and no sighters, or 20 minutes for 20 record shots. For team matches, 45 seconds per shot may be used.

At Camp Perry, the clock stops if the Guard has to send a boat out to chase away some ignorant boater who has ignored the buoys and gone into the bullet impact zone. Afterward, shooters are given time to get back into position, and the clock starts again. Normally, the RO orders "ceasefire" and "unload and make the line safe" before the Guard boat goes out. It sounds like somebody failed to obey that latter part of the command in the instance Bart is referencing. The only exception I recall seeing was a stop of the clock while a great blue heron flew across the firing line, after which it was started again without all the fanfare. Only a few seconds involved there, but enough to cook a round some.

[Bart B.]

Originally Posted by old roper

Bart, don't you get sighter and total time for all is 50 mins

Some matches don't allow sighters.

Sometimes a sighter is allowed if check fire time is longer than what rules cover.

Not aware of any 50 minute time rule in NRA's high power disciplines.

Download the NRA's high power rule book from:

https://competitions.nra.org/competi...es/rule-books/