Real life experiences regarding powder variations from lot to lot?

[Doodlebugger45]

I have read warnings that say that powder burn rate can vary by as much as 10% from one lot to another. And then I have read that it's probably more like 5%. Both of these numbers seem really high to me just from a seat of the pants point of view. I mean, from my days in college in quantitative analysis, 5% would be totally unacceptable in an experiment. They must have some QC going on in the shop right? Granted, the way they make powder is a bit more complex than what we were doing in school, but not by much.

In my own experiences, I have not seen nearly that much variation when moving to a new lot of powder. I do remember having to increase the charge weight of Varget by about 0.6 gr (1.5%) to attain the previous accuracy in a .308 and I remember having to reduce the charge of RL-22 by about 0.5 gr (0.8%) in a 270 WSM to keep the same groupings. But those were pretty minor things.

So, I ask, am I just lucky? Or just not observant enough? Have any others out there seen these extreme shifts of 5% or more going from one can to another?

[g.willikers]

It seems the powder measurers cause more variation than the powder.

[mehavey]

See

http://thefiringline.com/forums/show...ght=powder+lot

[TXGunNut]

I've never found a measurable difference. I seldom use a chronograph or max loads and generally check group sizes and cases when changing powder lots, which isn't very often. I generally buy 2-3lbs of the same lot for rifle powders and then I'm set for years. Had no idea such a large variation was deemed acceptable.

[scsov509]

I've seen the most significant differences in pistol powders, and in fact just recently cracked a new container of Unique that was dropping charges about 6-7% lighter than the previous container. I can't say I've seen it as much in rifle powders, but then again I'm also not going through rifle powder as quickly as pistol powder. But on the pistol side I go through a more powered in higher volume loading and have certainly seen some variation from one lot to the next. Then again, on the pistol side it doesn't take much variation in weight to make a big difference when you're talking lighter charge weights to begin.

[Doodlebugger45]

Very interesting experiment mehavey. Well done. I guess I missed that thread when you wrote it. A 3% change in velocity is significant. Maybe not the end of the world, but significant nonetheless. It's a reason for me to buy my powder in much bigger amounts. During the past year, it seems like those 1 lb bottles of powder seem to evaporate overnight. I strongly suspect that little gremlins come during the night and siphon off a 1/2 lb out of all the rifle powders every night to do mischevious deeds. No way can I be shoooting that much!

At any rate, thanks for the info. Like I said, it hasn't been a major problem so far, but those 2 examples will probably become more common if I go out and buy a couple of 1# jugs when I need them rather than biting the bullet and buying 16 lbs of my favorite powders each time.

[RC20]

I know this is an old thread but its finally occurred to me that is a good explain of why some loads have gone from very good to not nearly so good.

So one of my notes to myself is to start doing a chronograph test on my good loads and then if they change, I can check the velocity of what I have now and I know what direction to look in for return to that velocity (faster or slower)

And blending of new and old powders would seem to help the transition .

I buy 8 lb jugs now, it saves a few bucks, powders I know are mainstays.

I can't do that with 4I4451 (yet) but I can try to buy two or 3 at once ad that will last a fair amount of time.

[Metal god]

I did a test of IMR 4895 from one 8lb jug to another . I'll see if I can find that test data . I do remember there was a difference , how much I don't recall . The fact it was not enough to imprint a memory makes me think it was not much but then again that was just one sample . My thinking is the 10% difference is likely the fastest burn rate a powder was ever released at compared to the slowest burn rate that same type powder was ever released at . They try to make lot to lot differences minimal so the likely hood you having two lots at each end of that extreme is low but still possible . I'd add that the longer and more you reload a specific powder will likely increase the chances you come across that extreme .

[hdwhit]

Doodlebugger45 wrote:
I have read warnings that say that powder burn rate can vary by as much as 10% from one lot to another. And then I have read that it's probably more like 5%.

What was the source for these "warnings"?

They must have some QC going on in the shop right?

Yes, they do.

Granted, the way they make powder is a bit more complex than what we were doing in school, but not by much.

When you start talking about making nitroglycerin and nitrocellulose blends on an industrial scale, the complexity is much greater than what goes on in a college chemistry lab.

In my own experiences, I have not seen nearly that much variation

When both logic and your experience tell you the unsourced warnings are probably wrong, why extend them any credibility?

So, I ask, am I just lucky? Or just not observant enough? Have any others out there seen these extreme shifts of 5% or more going from one can to another?

Remember that second-hand metrics like "equivalent shot placements" or "velocity" have - at best - only a loose connection to the burn rate of the powder. The fact you had to increase powder charge by 1.5% to get the same shot placement doesn't mean the burn rate was 1.5% different. If you are equating the two, you are mixing apples and oranges.

[Nick_C_S]

Just from the seat of my pants:

This last # of Unique I just opened sure seems to be spunky. 357 Mag, 9.2 grains (a set charge weight I've used for several years - book max is 9.7 grains, I believe) under a Speer 125gn UCHP showed considerable signs of high pressure. Flat primers. Sticky extraction.

I stopped shooting them after three or four cylinder's worth. Took the remainder back to the range a few days later for a chronograph session, and they were running 1358 f/s (4" bbl). The load work up with the previous lot of powder yielded 1359 f/s. So velocities were the same; but I'm guessing the new lot yields a higher peak pressure for some reason. I'll let someone smarter than me figure that out. Mean time, my "set" charge weight of 9.2 grains has become 8.8 grains for this lot of Unique (I have another unopened # as well).

[Unclenick]

The last Hodgdon printed manual I got (12 years ago?) said that they hold IMR powder to ±5% burn rate and the Extreme powders from Australia are held to ±3%. Norma's manual says burn rate varies 12% depending on the humidity you store the powder in. People often make the mistake of thinking a sealed container prevents water vapor contamination completely, but even if the seal were so good it could stop the 0.275 nm water molecules from drifting through, the resin the plastic bottles are made from, high density polyethylene has a water vapor transmission rate (WVTR or sometimes MVTR, with M for moisture) of 0.5 ml/100in²/24hr. So the water content of the powder eventually equilibrates with the environment RH. So it isn't always the lot number that's at fault, but rather the storage history.

Understand, this is a different issue from bulk density. Bulk density can affect burn rate, but I've been told the test is done with a specific weight of powder.

[Nick_C_S]

So the water content of the powder eventually equilibrates with the environment RH. So it isn't always the lot number that's at fault, but rather the storage history.

This would explain why on at least three occasions, I have opened a new # of propellant - same lot number - and with the same hopper setting, threw a heavier charge. I live in the dry California central valley.

[BigJimP]

I think Relative Humidity is the culprit here too.../ and I heard years ago, let the new can of powder acclimate to your shop conditions ( pull the paper seal off the bottle and screw cap back on lightly)... especially if the relative humidity in your shop/reloading area is stable.

I can see this might be an issue on a 8lb keg I get from the SouthEast and it comes clear across country by UPS or US Postal...inside a corrugated box, that might get a little moisture on it from day to day...

( kind of like letting wood acclimate to your shop conditions before you start building a piece of furniture ).

I have not noticed any significant difference in the powder drops, by weight, between lot numbers...but the powder I use for handguns meters very well, Hodgdon TiteGroup.

[gwpercle]

If you load maximum and maximum plus loads ( some do) then new lots need to be worked up.
Most of my reloading is mid-range and target (light) loads so if a lot is faster , even 15 % , it won't be dangerous ...with these types loads I have never noticed any difference from one lot to another.
Gary

[RC20]

That's some dang interesting information.

And to add a kicker. Never store Super Glue in a sealed bag or conainter other than its origanl.

Why? Well that gets into what makes Super glue activae.

Its the LACK of air, the bottle it comes from is air permeable (how much I don't know, they have it figured out so no numbers per Unclenik)

I knew of one case where the stuff was stored in a sealed plastic bag, set up harder than a rock. Yep, de-provide of oxy and it did its thing, in the bottle!

Best place to store it is the fridge (which is also a good place for meds, does two things)
\
1. It preservers them

2. Thieves looking for drugs don't go through your fridge!

[k4swb]

Originally Posted by RC20

Best place to store it is the fridge (which is also a good place for meds, does two things)
\
1. It preservers them

2. Thieves looking for drugs don't go through your fridge!

May 2007. Thieves broke into my house and stole a Glock G30 and for some reason that still baffles me found my stash of prescription happy pills in my refrigerator. Also took a pack of cigarettes out of the carton but left the rest.

[Mobuck]

My thoughts: If you're burning a lot of powder and buying powder consistently, the variance may be less noticeable than if you buy 8# and don't buy again for 10 years.
There is merit to rechecking the loads when changing ANY component. The recommendation to drop 5% and re-shoot data may be that CYA statement the lawyers demand. I'll continue to reduce and re-shoot as I've already experienced a catastrophic firearm failure and don't intent to repeat that experience.

[cw308]

I mostly buy powder in 8 lb. Containers , if it takes 8 months to finish , would the powder be the same from when I first started to when it finished ?

[BillM]

Most powders have very little lot to lot variation. In my experience VihtaVuori
powders are very consistent. I use a lot of Hodgdon HS6--it can vary a bit.
Have had to adjust powder .1-.2 gr. to get the same velocity (on a 8.8 gr charge)
Biggest variance I have seen is with Accurate Solo 1000. I've seen it vary 10%
(.4 gr) from lot to lot.

[Unclenick]

Powder is always deteriorating and the stabilizers scavanging the breakdown products. So, no, it won't be exactly the same. However, if you are not storing it at elevated temperatures, most of the time the difference will be undetectable except by an analytical laboratory over such a short period. Most of the time. Here are a couple of exceptions:

One is that the powder is chemically close enough to identical, but you changed the humidity level substantially. Norma has measured a change in burn rate of about 12% going from about 0% to 80% RH in storage. They ship the powder after keeping it at close to 50% RH, so if you got the powder from the factory quickly, it might start there and switch to your conditions.

Norma says it takes about a year for water levels to equilibrate with outside humidity in a loaded cartridge, so this is with water gradually slipping past the metal contact surfaces between the case and the bullet and primer cup. I don't see a reason to the the lid on a powder container is a better seal than those, so I would expect changes along the same order of magnitude, time-wise, in a powder container.

The other worst case possible problem has to do with getting a bad lot of powder. Every once in awhile the powder companies mess up, adjusting the burn rate by blending with a held back lot of the same powder type that was allowed to get too old before they blended it in, so all of its stabilizer was already used up and it was generating breakdown products too fast for the stabilizers in the newer powder to keep up with the scavenging. There have also been incidents in which, somewhere along the line, someone stored the powder in shipping containers that were exposed to sunlight and which can get as hot as 170°F inside in some locations. I've seen several reports of there having been a lot of IMR4350 around 2000 that would give obvious deterioration signs within two or three years of purchase. The same with a lot of Vihtavuori N140 from back in the 1990's. More recently, there was a recall on some lots of IMR4007SSC for premature breakdown. If you had the misfortune to get a lot like one of these, then 8 months could make a lot of difference in performance, but you should see obvious breakdown signs, like acrid smell or reddish dust coming off the grains.

Note that the main danger from breakdown is that it will break down the deterrent coatings faster than the nitrocellulose in the powder. That leads to a powder with a faster burn rate than it originally had, which can and does cause high pressures. In a couple of extreme cases, even gun bursts. So never load with a powder that has started to deteriorate, thinking you can still get a last set of loads off it. That is just asking for damage.

[cw308]

Unclenic
Thanks for answering my question.