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Difference between two batches of powder

09 Jan 2023
@ 03:39 am (GMT)

Peter Bjerregaard

Hi All
Just a short write-up of my latest “findings”.

When at the range it occurred to me, I had two rounds left from the very last of an old can of powder. And a bunch of cartridges from a newly opened can. Two cans, different batch #, different age and “open-time”. Why not test it?

Shot new and old rounds intermixed. Range 100 meters. Kongstad electronic target.

Double-grouping. Note each group very small ~ 0.15 MOA/ 4 mm center to center. No shooter error.
ES between groups 36 mm/1.4 inches = 1.2 Moa @ 100 meters.

There might be batch differences, but Norma has a reputation of very little difference between batches.
First working hypothesis: Different relative moisture content.

From “Allt om krut & lite till” by Sven-Eric Johansson. (“All about powder and more” by a former Norma engineer) RP15 = MRP.

Powder is hydroscopic. A new can of powder is in equilibrium with a relative moisture content of 40-50. During summer in Denmark typical values are 60-65 indoors. In winter 40-45. The “old” rounds were made late summer when moisture content in the air peaks. If we hypothesize a difference of 10% rH -> difference in V0 of 0.5-1 %. This should lead to a difference @100 meters of a few mm’s.

Second hypothesis: Purely batch difference. Might also be true.

Are the differences enough to alter barrel harmonics? I do not have the answer, but the result might make you go hmmm… And should lead to always check a new batch at the range. Or even an old can that has not been used for some time.
And especially in summer: Do not leave powder out in the air to long.

My thanks to Grant @True-Flite for the barrel and accurizing my old K98 action. Otherwise, I wouldn’t have been able to do this.



28 Jan 2023
@ 10:27 am (GMT)

Nathan Foster

Re: Difference between two batches of powder
Hi Peter, thanks so much for taking the time to post your experiences and supportive information. Very much appreciated.


We are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.