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How much does powder vary from lot to lot.

 
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Old 04-24-2008, 06:34 AM
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How much does powder vary from lot to lot.

I just worked up a good load for my 300wm using IMR7828,the problem is,I started with a 1lb. bottle and now I need to buy more.I want to buy a 8lb. jug so I will be set for a while.Should I expect a difference between the 2 different lot #'s of powder?If so,what should I do about it?I was thinking about using my chronograph to get the new powder to shoot the same as the old,by tweeking the load with the new powder.Is that the right thing to do?
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Old 04-24-2008, 07:49 AM
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"How much does powder vary from lot to lot."

That's a broad question. We have quite a few makers and each produces more than a few powders, and they never tell us how broad a range they accept for cannister powder lots.

Bottom line, it's up to each us to determine if a new lot is much the same or a little faster or slower than a previous lot. But, I've never loaded up to the ragged edge of full pressure, as gaged from signs, so I don't worry about it. Never had a problem, never needed to tweak a charge to get good accuracy from an older load or powder lot.

I'd load a couple of rounds normally with the new lot and fire them, examine the cases for pressure indications and, if all is well, stick with that previous load.
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Old 04-24-2008, 08:44 AM
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I would err on the side of caution and work up to the same velocity as you planned. I have seen some pretty big swings in lots of powders imported in different years say from 04 vv133 to 07 vv133. The age and storage of the older powder may have played a role, I dunno, but the older powder is way slower. I dont think the variance I have seen would be enough to be dangerous unless you were right on the ragged edge with a slow lot and then switched to the same loading of a faster lot.
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Old 04-24-2008, 09:07 AM
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I always drop about a full grain and work back up in 1/2 grain increments checking for signs of pressure and chronographing these loads. Doesn't take much time. The 5 and 8 pound kegs are the way to go.
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Old 04-24-2008, 12:53 PM
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Quote:
Originally Posted by KQguy View Post
I just worked up a good load for my 300wm using IMR7828,the problem is,I started with a 1lb. bottle and now I need to buy more.I want to buy a 8lb. jug so I will be set for a while.Should I expect a difference between the 2 different lot #'s of powder?If so,what should I do about it?I was thinking about using my chronograph to get the new powder to shoot the same as the old,by tweeking the load with the new powder.Is that the right thing to do?
Absolutely. Every powder and every maker puts lot numbers on powder for a reason. The reason is because they can't make two batches of any powder exactly the same. Vihta Vuori powders are probably the most consistent from lot to lot but as eddybo mentioned, they still aren't exactly the same. Alliant is the worst in my experience for lot to lot consistency. I have seen as much as 3% variation in these powder's burn rates and that is like the difference between RL19 and RL22. So if you worked up your load with a slow lot of RL22 and then buy another lot and it is on the fast side of 3%, now your working with a whole new animal. Re-testing is crucial.

Let's say you find a load with RL22 that has great standard deviation and produces tiny groups and it is 65.5 grains. You also notice that the velocities go up roughly 55 fps with every .5 increment charge around 65.5 and the load above and the load below give average accuracy and average deviations. Then you buy another lot of RL22 and it is slightly faster burning. Well, now it has bumped you up 100 fps at the 65.5 grain charge and the accuracy has gone away. So you have to reduce the charge to 64.5 grains or thereabouts to get the speed and harmonics(accuracy) back. This is very common.

Hope this helps.
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Old 04-24-2008, 01:07 PM
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Should I be able to get as good of a load as I did with the original powder?I know I will probably have to tweak it a little.My original load was shooting an ES of 12,and SD of 4(4shots).I just want to make sure I can still get those kind of numbers from a different lot#.
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Old 04-24-2008, 01:46 PM
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Quote:
Originally Posted by KQguy View Post
Should I be able to get as good of a load as I did with the original powder?I know I will probably have to tweak it a little.My original load was shooting an ES of 12,and SD of 4(4shots).I just want to make sure I can still get those kind of numbers from a different lot#.
You shouldn't have any problem with IMR. Most of the time, I can duplicate the performance with a little tweaking. Sometimes, I have seen Alliant not quite get the same accuracy but velocities would be similar.
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