Mixing powders of the same type

[eb in oregon]

My opinion. Much has been said and written of mixing powders.

The first rule is never ever mix two unlike powders. Which is not the same as duplex or triplex loads. Those are carefully layered. Mixing two different powders is a really bad idea.

So that takes us to mixing powders of the same brand and type. For example: Unique is Unique. H110 is H110. Any specific powder is essentially the same as the can just run out before that run of reloads are done. I'd offer the thought that all lots of powder must meet certain criteria to meet industry or factory standards. So each and every lot of that particular powder must meet the standards. As such, one lot 10 years older will mix with a new lot as they were both manufactured to specification.

There is the matter that on occasion a particular lot proves to be more consistent, which is what target shooters look for. However for the average guy using a new can on top of an old can means nothing. In 40 years that thought has not been proven wrong.

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[drstrangelove]

One notable exception… Alliant Steel, lot #14 came very close to ballistic deconstruction… 3500psi over safe max in a pre14 published load… compared to other lots it was at least 25% more recoil in my gun, and required a 10% reduction in powder to equate prior lots. That was subsequently quietly corrected by mnfr w.o them admitting fault.

There may be other instances with other powders… I only happened upon this because I was just into SG reloading and was reading everything.

 

[eb in oregon]

Alliant Steel, lot #14 came very close to ballistic deconstruction

True, but that wouldn't affect all powders nor would that have made a difference if dumped onto a different lot. Things happen.

 

[drstrangelove]

The dilution of uncertainty is one way to deal with it. Just saying YMMV especially if some powder is way older than the new powder. I would rather use up a know entity if hopes of keeping groups small and pheasants falling rather than pieces of shotgun. Ladder loads and SG patterning are your friends.

 

[P7M13]

Ladder loads and SG patterning are your friends

This. Due diligence in load development is required.
I have not encountered much variance from one lot to the next. Back in 2012-2013, when it was hard to find more than a bottle of powder at a time, I would test different lots, then blend the two, and develop my load from the blend. It works well for me.