Powder Lot Velocity Change?

[chkunz]

I am seeing a velocity change of approximately 50 fps in one of my 223 pet loads. One possibility is that this change is the result of a change in powder lots. This pet load is with Reloader 15. Has anyone measured a velocity difference of this magnitude when changing powder lots?

I have recently started using a chronograph to assist in load development. It may just be that I am now seeing things that have always been there but since I was not measuring them I had no way of knowing.

 

[dkhunt14]

Yes have seen major changes. I had a lot of Varget that was slow. I also had a lot of RE22 that was dangerously hot. It was a couple hundred feet fast. Other things like the reading on the chrono., time of day you shot and temperature can change it some. Matt

 

[Shynloco]

Yes have seen major changes. I had a lot of Varget that was slow. I also had a lot of RE22 that was dangerously hot. It was a couple hundred feet fast. Other things like the reading on the chrono., time of day you shot and temperature can change it some. Matt

I can certainly echo what dk wrote. Lot changes can cause all sorts of havoc. IN ADDITION, ambient temps and other physical and atmospheric factors can take a great load and turn it into a mediocre or worse one. And you'll scratch your head wondering what happened. So whenever I change lots of any powder, I retest (briefly) to see if my previously loads still hold up or do I need to start anew in terms of work up. I will say if accuracy is suddenly slightly off, I change a few tenth of powder either way and see if that cures the change in powder lots. Just my thoughts.

 

[lawrence97]

When starting out with a new powder lot I always drop the charge a tad and verify with the chrono and bump it up or drop it to match my last load.

 

[Twoboxer]

I am seeing a velocity change of approximately 50 fps in one of my 223 pet loads.. . . This pet load is with Reloader 15. Has anyone measured a velocity difference of this magnitude when changing powder lots?. . .

Last week, running low on my 8lb jug of HP38, I began tests on a new batch of 10lbs. To maintain my pet load's velocity I needed a 3%-4% INCREASE in powder. The opposite direction and different basis for measuring, but you are experiencing a (eg) 1.9% change (in fps) if your original velocity was (eg) 2700fps.

 

[KevinThomas]

Never forget that smokeless powder is an organic compound. While the chemists at the plants can match burning rates within a particular range, it's not exact. There will usually be some degree of variation from one lot to the next.

 

[chkunz]

Never forget that smokeless powder is an organic compound. While the chemists at the plants can match burning rates within a particular range, it's not exact. There will usually be some degree of variation from one lot to the next.

Thanks for the reply and I understand completely and have read this many times but this is the first time I have used a chronograph to measure what is going on and I am trying to understand how much velocity is effected by things like lot to lot variations, temperature variations, etc. Can you quantify any of the changes that you have experienced?

 

[chkunz]

Yes have seen major changes. I had a lot of Varget that was slow. I also had a lot of RE22 that was dangerously hot. It was a couple hundred feet fast. Other things like the reading on the chrono., time of day you shot and temperature can change it some. Matt

Thanks for the reply. Since I am using a chronograph for the first time I am trying to quantify the effect some of these variables have on velocity. It also bothers me greatly that I have no way to calibrate the chronograph so I have no way to separate the errors form the variability of the instrument.

 

[chkunz]

Last week, running low on my 8lb jug of HP38, I began tests on a new batch of 10lbs. To maintain my pet load's velocity I needed a 3%-4% INCREASE in powder. The opposite direction and different basis for measuring, but you are experiencing a (eg) 1.9% change (in fps) if your original velocity was (eg) 2700fps.

Thanks, it sounds like a 2% change in velocity lot to lot is not unusual?

 

[KevinThomas]

Thanks for the reply and I understand completely and have read this many times but this is the first time I have used a chronograph to measure what is going on and I am trying to understand how much velocity is effected by things like lot to lot variations, temperature variations, etc. Can you quantify any of the changes that you have experienced?

The only report I've ever seen done on this topic was from IMR some years back, and they cited velocity changes of 1.7 fps per degree of temperature change, up or down from an nominal 70 degrees. As for variation in relative quickness from lot to lot, I suspect that may be something that's used within the manufacturers themselves, but hasn't been published. No where that I've seen, anyway. For a canister grade powder, they have to maintain it within a range that will be safe with existing published data, but we seem to be talking about somewhat more minute changes here. Exactly what those parameters may be, I don't know.

 

[Twoboxer]

The only estimates I've seen for lot variance is +/- 5% from target, probably a bit conservative. But which can be a 10% swing. And has probably contributed a bit to "start 10% below max and work up".

IMO, a 2% powder charge change is not remarkable at all. And I'm not sure what your powder charge was and would need to be to get your usual velocity. But it's probably even less than a 2% powder charge change.

 

[Shaggy357]

If I use an 8 lb canister of powder for primarily one gun, I always ensure I have a new jug available before I run out of loaded ammo. As I work up the load with my new lot of powder I can compare new reloads, with existing ammo. Temperature, humidity, elevation, and chrono reading variability should be minimized by shooting both loads on the same day. Least amount of shooting variability will make the confirmation of lot to lot variation in the powder much faster and easier.

 

[dmoran]

Load a few up to both your current Lot and the new Lot at one in same safe/conservative charge, and shoot them alternating between the two, in the same test session. The POI and chronograph (if you have one) will show the significance between the two.
Or is how I go at it.....
Donovan

 

[Eric Leonard]

I switched lots of H4350 last summer and in my BRDX load of 36 grs and CCI450 primers and 105 VLDH bullets,at 3020 fps,had shot over 1,000 rounds same lot,,first shot with new lot blew primer out of case,,had to back down to 34.8 to hit that speed and it wouldnt group for crap,,

 

[chkunz]

Load a few up to both your current Lot and the new Lot at one in same safe/conservative charge, and shoot them alternating between the two, in the same test session. The POI and chronograph (if you have one) will show the significance between the two.
Or is how I go at it.....
Donovan

Great recommendation, thanks.

 

[chkunz]

If I use an 8 lb canister of powder for primarily one gun, I always ensure I have a new jug available before I run out of loaded ammo. As I work up the load with my new lot of powder I can compare new reloads, with existing ammo. Temperature, humidity, elevation, and chrono reading variability should be minimized by shooting both loads on the same day. Least amount of shooting variability will make the confirmation of lot to lot variation in the powder much faster and easier.

This is a great recommendation, thanks.

 

[amamnn]

You'd be surprised at how much the density of you powder can vary from lot to lot. This is especially true of the flakey powders and of Alliant in particular. There is nothing inherently bad or dishonest or sloppy about this fact--it merely needs to be noted and action taken to negate any deleterious effects caused by this variation. Serious shooters at some point learn to buy their powder in quantity to avoid having to recheck density and adjust loads. This being said, a 50fps variation in your MV is well within tolerance and margin of error when using ANY chronograph to work up a powder charge......in many people's opinion, a waste of time and money to begin with, but that is another can of worms.

Anyway, if you are seriously concerned about lot to lot powder density, you can actually measure it with tools and instruments readily and inexpensively made available to hand loaders. You will need a powder dipper of known volume as expressed in cubic centimeters (CC) and a scale capable of measuring weight in grams (G) most digital scales will do this. The better scales will have check weights included at purchase, which is something you want. This whole process can be done with imperial or US Customary measure (drams, ounces etc.) but the numbers do not crunch easily, as they do in metric measure. If you actually do this, you will see why the big dome rocket sceintists all use the metric system; they're rocket sceintists, they're not stupid; they don't like wasted time and energy any more than you do.

SOUNDS COMPLICATED BUT IS SIMPLE TO DO

So, what we want is a measure of the actual density as related to mass, but don't worry about the relatives that's what motel 6 is for they can stay over there, (using weight/volume) of the powder and luckily, in the metric system there is a sort of check density against which all density can be compared. The magic check substance is plain water (ideally pure, but tap water works just fine unless you live in Gila Bend, AZ) In the metric system water has the known mass of----ready?----1 (one)---and the comparison of the known volume of your powder as carefully scooped, and the weight of that volume will give you the density (mass, sorta ) of the powder as compared to water. This is easy to do in because a cc and a gram use the same measuring stick unlike ounces of weight and ounces of volume (fluid ounces) So---we carefully scoop our powder (Lee scoops work quite well) and drop it on our scale. and do a little tiny harmless painless math. You may even use a calculator like the one on your computer.

You do this------->divide weight (G) by volume (cc) and you get a fraction which tells you how dense your powder is compared to water. So, 2 grams of powder by weight divided by 2.2 cc of powder by volume equals .909 or 90.9% of water density. You write this on the jug of powder and when you buy a new jug you do this again. Or you can just buy powder from someone who keeps tolerances closer. BTW, don't divide cc by G that will not give you the info you want--AND--there are powders that are denser than water, so it is possible to get an answer over 100%

All in all a fun way to top off a rainy afternoon after checking case weights and volumes of a few hundred pieces of brass--or you could just buy Lapua or Noma to begin with..............