@ 03:39 am (GMT)
Peter BjerregaardHi 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 mms.
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 wouldnt have been able to do this.
@ 10:27 am (GMT)
Re: Difference between two batches of powderHi Peter, thanks so much for taking the time to post your experiences and supportive information. Very much appreciated.