Powder lot-to-lot variation

[alzo]

I'm just curious....for those of you who check such things, how much variation have you noticed switching from one lot to another of a particular powder ? Was the variation enough to cause you to alter your load ?

 

[ReloaderFred]

I've only had to alter a load once due to lot variations since starting to load in 1963. That was in the late 1970's, when changing over to a new keg of Winchester 748. For that keg, and that one only, I had to drop my load for .223 one full grain.

I usually try to buy my powder by at least the 8 pound keg, and usually by the 32 pound case, just so the lot will be consistant for the greatest number of loads.

Hope this helps.

Fred

 

[The Bushmaster]

Now days powder really doesn't chage that much between lot numbers. But with that said...Keep an eye for the one that does. I usually load mid range for a new lot and compare it over my chronograph. If it is within reasonable fps of the last lot then I proceed to load as usual...

 

[alzo]

Thanks for the replies. I thought there would have been more. I wonder if that is indicative that most people don't recheck their loads when switching lots, or indicative of nothing at all.

 

[243winxb]

No variation using IMR powder for year. The company blends many batches of the same powder to make one lot number.

 

[Walkalong]

The powder companies go to great lengths to get each cannister lot the same. They have to.

That said, always check a new lot.

 

[Larry E]

Some powders are really consistant from lot to lot, others less so and by enough to make things sticky. It never hurts to do a little pressure check when going to a new lot of powder unless you're loading well below maximums. Since I tend to push the limits I check pressures when changing powder lots. Haven't blown anything up in 38 years either.

 

[The Bushmaster]

Curious Larry...But how do you check pressure?

 

[ReloaderFred]

Larry sneaks into your place at night and tests his new loads through your guns.............

Fred

 

[Ol` Joe]

A good way to insure the pressures from a new lot of powder are comparable to your old is to chrony a load that is about 1.5-2 grs lighter then your max charge. When you get a new canister of powder load up the same charge and recheck with the chrono. If the velocities are very close you can figure the pressures are also, and go to your regular loading. If there is a wide spread in the velocities between the two loads the pressures are likely quite varied also. I`d work the load back up in this case.

BTW, I`ve read the industry standard is a 10% total allowed variation in powder burn rate. (+/-5%) Some are better, some are close to the allowable tolerance.

 

[The Bushmaster]

I was wondering why my guns got dirty and I never had them out of the safe...

 

[Clark]

My experience is that IMR and Alliant powders are so close lot to lot that the difference cannot be measured in velocity or threshold or long brass life. The spread in a group overlaps the spread of a group from another lot. This is a variation of less than 1%.

Sometimes I think AA powder is really surplus bulk powder with a 10% variation.

But then, the experiences of one handloader, me, is purely anecdotal.