Changing to new batch of powder- what safety margin do you need?

Hi all, if I have a load worked up and I am changing to a new batch of the same primers and/or new batch of same powder, how much do I need to back off. I have a mild load for my 458 lott which was a few grains off maximum. It is 2195 fps and maxes out around 2270 fps. So basically it is not close to max load. Do you back off to minimum or do you have a safe percentage from maximum where it is OK to load and then use a chronograph to check ?

You talking just different lot of powder but same type? Just load how you normally would.

I agree. Never heard of anyone backing off when using newer powder or primers of same type. Possibly might be something target shooters or long range metal bongers might be worried about. Not for hunting loads.

Ontario Hunter said:

I agree. Never heard of anyone backing off when using newer powder or primers of same type. Possibly might be something target shooters or long range metal bongers might be worried about. Not for hunting loads.

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Nah different lot will affect percormance a bit. But thats why you just re confirm 0 its not going to be anuthing worth worrying about

farmer_john said:

Nah different lot will affect percormance a bit. But thats why you just re confirm 0 its not going to be anuthing worth worrying about

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I was agreeing with you.

Nhoro, since you are using the same powder with no changes in brass, primers or bullets I'd load a few rounds using your current load, say 5 or so and run them over a chronograph as well as check them for group sizes. I doubt you will see a significant difference.

Nhoro said:

Hi all, if I have a load worked up and I am changing to a new batch of the same primers and/or new batch of same powder, how much do I need to back off. I have a mild load for my 458 lott which was a few grains off maximum. It is 2195 fps and maxes out around 2270 fps. So basically it is not close to max load. Do you back off to minimum or do you have a safe percentage from maximum where it is OK to load and then use a chronograph to check ?

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Great question. This is just what I do with great confidence. I use Quick Load software. I had a chance to talk to the inventor of the software and she told me they are very conservative in their recommendations due to legal concerns. Therefore I always first choose my desired FPS as my starting point then second ensure it is with QL PSI max. just me

Nhoro said:

Hi all, if I have a load worked up and I am changing to a new batch of the same primers and/or new batch of same powder, how much do I need to back off.

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You would do yourself well to pay close attention to any powder changes, even within the same lot #!

And this goes especially for any of the Reloader and Accurate Powders. No two kegs are created equal, even within the same lot#. Years ago I started blending most of the powders I use. I am fortunate, I actually run pressure equipment here and able to get pressure data. Like most of us, I have been lazy at times, and just used the same load I had previously done pressure work on, when getting a new batch of powder, this caused an issue and an increase of 10000 PSI as well. And when you are working at 45000 PSI, an increase of 10000 PSI is subtantial and could lead to problems. On this particular load which was 42 grs of this powder, I had to back down to 39 gr to equal the previous 42 gr load. On another occasion in a larger caliber I had worked up loads that were perfectly safe at 62000 PSI with a 115 gr of this powder, from One, 5 lb keg. I eventually used that 5# Keg, and started with another one, but fortunately I did drop the charge. Had I used the 115 gr load with the new 5# Keg, it would have blown the rifle. I had to drop to 95 gr of the same powder, new keg, to equal the same velocity and pressures! On the next 5# keg of the same powder, it had to be lowered to 85 gr to equal.............. This could have led to a dangerous failure. I had to start load data on this cartridge over, and had to discontinue use of that powder completely. I still look for that very first Magic 5# keg, even blending different powders together, but I have yet to be successful in finding that magic 5# Keg that I started with.

I have not seen extreme changes in the IMR, Hodgdon, Winchester, or Ramshot powders. Minor differences yes, but nothing that would cause extreme concerns.

Regardless however, I blend all Reloader and Accurate powders. I blend IMR, Hodgdon, Winchester and Ramshot powders that I tend to use a lot of. Those that I do not use a lot of, I watch and test carefully when changing from Keg to Keg. I don't even pay attention to Lot#s anymore, I have seen major differences within the same lot#. We must keep in mind, before we receive a given powder, we do not know how it has been kept and the environment it has been kept in previously.

I have a clean uncontaminated 5 gallon bucket I use to mix and blend in. RL 7 is a powder I use a lot of, so I normally purchase 15+ lbs, pour it all in the bucket, mix it up thoroughly, and repackage it, and label it the day or month blended. Then it is off to the range and using the pressure equipment test the loads for the New Batch. Data kept from then on in that cartridge, references the Batch Date in each entry.










Accurate 2230 is not a powder I use much of. It is or has been decent in 458 Winchester, and that is all I have ever used or tested it in. In 2013 I did a lot of data work with 458 Winchester and used some 2013 Vintage AA 2230 in some of that work. I had previously found some serious differences from 2011 Vintage AA 2230 to 2013 Vintage, by 3-5 gr of powder and 5000-7000 PSI. In 2022 I wanted to do some new 458 Winchester pressure data and elected to purchase some new AA 2230 for that. I did a comparison between 2013 Vintage and 2022 Vintage, and found the 2022 Vintage gave 5000 PSI less pressure than the 2013 Vintage, with only 30-40 fps less velocity with the same bullet. This was a plus I suppose. But, it shows you cannot just change powders without checking it and using safe practices.



And below, you can easily see a vast difference in the two Vintages of 2230.




Yes, making a powder change, I would pay very close attention, not just Lot# to Lot#, but from one can of powder to the next. I strongly recommend using larger 5# + kegs instead of 1# cans. Yes, you should drop by 10% to test. At minimum. If below where you were, work your way back to the velocity you were getting.

Primers within the same make and #, has never shown to be an issue. For instance, I have never seen a major difference in Federal 215s from one to another. Primers can be an issue if you were going from Federal to say Wincheser or CCI, or reverse.

Brass can be a big issue too, I think I have seen more of a difference in changing from one manufacturer of brass to another than primers. All brass is not created equal.

Michael458 in my case, my load is already around 10% below max. Considering the pressure curve, it is more than 10 %short of a no pressure signs load. So I think I have the reduced load already

Having worked in the industry, please allow me to post the following.

For Winchester and IMR propellants (and probably most others), the manufacturer achieves lot-to-lot consistency by using what is called a Reference Lot. Upon making a lot a particular propellant, the new lot is tested alongside the Reference Lot. Only those lots that meet very narrow requirements for density, velocity, and pressure compared to the Reference Lot area designated “Canister” and released to the reloaders. This process ensures that reloading data remains relevant and the expected velocity is achieved with safe pressures. Incidentally, those powder lots that do not meet the requirements for Canister are used for factory ammunition where pressure and velocity are controlled for each application.

Most all loading books warn to back off loads 10% from maximum when changing ANY components.
I usually don't and have had no adverse surprises, but generally am using components of the same lot numbers.
Some powders do change quite a bit over 10 years, as noted above.

It is good to have someone on board here who does a lot more reloading than me. I'm sure I have not shot fifteen pounds of rifle powder in my lifetime and I've been shooting and loading since 1964. But again, I doubt the variations in zero and/or pressure encountered when changing to a different supply of the same powder would be significant if one is not pushing the envelope to start with. Or looking for match grade performance in the next zip code. It seems most of the recommended "max" loads in the factory manuals/data sites are well below the actual "red line." MEC shotgun loading data for their bushings is WAY below anything that would be dangerous, in my experience anyway (which is MUCH more extensive than my rifle reloading experience). Perhaps this is the reason why? If there are pressure variations within lots, the manufacturers surely want to recommend reloaders stay well below the potential danger zone. Best way is to be conservative when publishing maximum load data.

My own loading started back in 1968 with a 6.5 Rem Mag. I think I put over 15 pounds of powder out of that, the 1969 through 1972 BRNO Fox Hornet and Ackley .22-250 before Apr. 1972 when I joined "The Force".
The last powder I reduced before loading back up, was Re#7. The old powder I was using in my .17AckHornet was all grey/brownish, small short kernals. I'd worked up some good loads with it running the then-new 25gr. Vmax at 3,640fps. I ran out of the original 4 pounds I had and the new powder, another 4 pounds looked like it was the old powder mixed with some IMR4198. That spooked me a bit. I then checked more of the new lot in a local gun shop in 1 pound cans and it was identical to the new Re#7 I had purchased. I reduced the load by 1 1/2 gr. and then worked back up to my original load in 2/10gr. increased, according to my memory, 12.3gr. as max again. Accuracy restored and so was the velocity.

For hunting purposes I don’t bother backing off. I have even used different lots when using up a bottle and here can be a difference In minute ES or SD numbers but for what your using the accuracy won’t change.
Guys who are deep into consistency will definitely back it off and re-confirm the load though.

@Nhoro, I didn't see the type of powder you were using. I'm reminded of the fact that you might not have access to the powders we are accustomed to using. I have a number of AH buddies that live in Africa and complain bitterly about the lack of consistency with Somchem powders. My friends tell me that they have to call the factory to get comparisons between two or more lots of the same type of powder.

Great thread. I learned something new.
I thought I was a reloading geek but @mdwest running pressure tests is very cool. Mixing is also a new one to me to homogenize across pound increments. Bravo!

My only contribution to the thread is that whether you trust the manufacturer to control variation or not, you'll have less if you buy the larger containers (or blend them)

I buy by the pound during development trials and then buy in 8# jugs when finished with the expectation of minor adjustment initially from the big jug.
I don't reduce my loads but I don't load very hot. I probably should though.

Another consideration to minimize variation is to realize powder is hydrophilic and storage environment matters.
A .50 cal ammo can holds most 8# jugs airtight and they're protective.

Cool and dry for powder storage. If the powder has rust in it or smells strongly acidic, it has deteriorated. Makes good fertilizer in that condition, aparently.
I just opened previosly unopened can of IMR 4198 and it was rusty, has red rust in it. After the snow melts and the ground thaws, I'll spread it in ghe garden.
The can was the old steel, so was quite old.

Nhoro said:

Hi all, if I have a load worked up and I am changing to a new batch of the same primers and/or new batch of same powder, how much do I need to back off. I have a mild load for my 458 lott which was a few grains off maximum. It is 2195 fps and maxes out around 2270 fps. So basically it is not close to max load. Do you back off to minimum or do you have a safe percentage from maximum where it is OK to load and then use a chronograph to check ?

Click to expand...

I have never changed loads just because I bought a new can of the same powder or a new batch of the same primers. I do check the zero just to make certain that the zero hasn't changed, but I don't remember any occasion when there was much of a difference. I wouldn't worry about it.

michael458 said:

You would do yourself well to pay close attention to any powder changes, even within the same lot #!

And this goes especially for any of the Reloader and Accurate Powders. No two kegs are created equal, even within the same lot#. Years ago I started blending most of the powders I use. I am fortunate, I actually run pressure equipment here and able to get pressure data. Like most of us, I have been lazy at times, and just used the same load I had previously done pressure work on, when getting a new batch of powder, this caused an issue and an increase of 10000 PSI as well. And when you are working at 45000 PSI, an increase of 10000 PSI is subtantial and could lead to problems. On this particular load which was 42 grs of this powder, I had to back down to 39 gr to equal the previous 42 gr load. On another occasion in a larger caliber I had worked up loads that were perfectly safe at 62000 PSI with a 115 gr of this powder, from One, 5 lb keg. I eventually used that 5# Keg, and started with another one, but fortunately I did drop the charge. Had I used the 115 gr load with the new 5# Keg, it would have blown the rifle. I had to drop to 95 gr of the same powder, new keg, to equal the same velocity and pressures! On the next 5# keg of the same powder, it had to be lowered to 85 gr to equal.............. This could have led to a dangerous failure. I had to start load data on this cartridge over, and had to discontinue use of that powder completely. I still look for that very first Magic 5# keg, even blending different powders together, but I have yet to be successful in finding that magic 5# Keg that I started with.

I have not seen extreme changes in the IMR, Hodgdon, Winchester, or Ramshot powders. Minor differences yes, but nothing that would cause extreme concerns.

Regardless however, I blend all Reloader and Accurate powders. I blend IMR, Hodgdon, Winchester and Ramshot powders that I tend to use a lot of. Those that I do not use a lot of, I watch and test carefully when changing from Keg to Keg. I don't even pay attention to Lot#s anymore, I have seen major differences within the same lot#. We must keep in mind, before we receive a given powder, we do not know how it has been kept and the environment it has been kept in previously.

I have a clean uncontaminated 5 gallon bucket I use to mix and blend in. RL 7 is a powder I use a lot of, so I normally purchase 15+ lbs, pour it all in the bucket, mix it up thoroughly, and repackage it, and label it the day or month blended. Then it is off to the range and using the pressure equipment test the loads for the New Batch. Data kept from then on in that cartridge, references the Batch Date in each entry.

Accurate 2230 is not a powder I use much of. It is or has been decent in 458 Winchester, and that is all I have ever used or tested it in. In 2013 I did a lot of data work with 458 Winchester and used some 2013 Vintage AA 2230 in some of that work. I had previously found some serious differences from 2011 Vintage AA 2230 to 2013 Vintage, by 3-5 gr of powder and 5000-7000 PSI. In 2022 I wanted to do some new 458 Winchester pressure data and elected to purchase some new AA 2230 for that. I did a comparison between 2013 Vintage and 2022 Vintage, and found the 2022 Vintage gave 5000 PSI less pressure than the 2013 Vintage, with only 30-40 fps less velocity with the same bullet. This was a plus I suppose. But, it shows you cannot just change powders without checking it and using safe practices.

And below, you can easily see a vast difference in the two Vintages of 2230.

Yes, making a powder change, I would pay very close attention, not just Lot# to Lot#, but from one can of powder to the next. I strongly recommend using larger 5# + kegs instead of 1# cans. Yes, you should drop by 10% to test. At minimum. If below where you were, work your way back to the velocity you were getting.

Primers within the same make and #, has never shown to be an issue. For instance, I have never seen a major difference in Federal 215s from one to another. Primers can be an issue if you were going from Federal to say Wincheser or CCI, or reverse.

Brass can be a big issue too, I think I have seen more of a difference in changing from one manufacturer of brass to another than primers. All brass is not created equal.

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thank you, sir for that informed insight

I would suggest that if your loads are not top-end book loads, then you likely dont have to change anything, however you should check your new loads for accuracy and point of impact.