Node interpretation

[Gregor.Samsa]

I just began load development on a new rifle/ barrel (6 creedmoor, 26" proof barrel). I am following Erik Cortina's PRS load development advice where he tested primer & powder combos using a 10 shot method.

https://www.patreon.com/ErikCortina/posts?filters[tag]=PRS%20Load%20development

I realize that 1 shot for each powder charge is not enough statistical evidence to draw a full conclusion, but it should show a pattern and that's where my question lies. I am testing 105 berger boat tails (not hybrids) vs Barnes 112 match burners and also testing h4350 vs n550 as I've been able to obtain some n550 and my h4350 supply is dwindling. The test results show that h4350 to spike and plateau in terms of velocity whereas the n550 is more linear and flatter in this regard. I was not shooting for groups at all but The n550/ 112 match burner combo shot lights out event with the different powder charges but had a lower velocity. Is the flatter, more consistent nature of the n550 a good thing or does this display a lack of a node and would I be better off selecting a charge within h4350's plateaus? Thanks

 

[Newbie2020]

Wrong conclusion. You’re assuming the powder charge left a flat spot when it’s actually the accumulation of the myriad tiny loading variances which created the “flat spot” or “plateau”.

Flat spots are a myth. Increasing charge weight in a linear fashion yields a concomitant linear increase in pressure and a subsequent linear increase in muzzle velocity.

Either pick a charge weight based on desired velocity, or find book value for max pressure and back off 0.5 gr. Tune seating depth to tune barrel harmonics and precision.

 

[Gregor.Samsa]

That makes sense. thank you

 

[Gil P.]

There are lots of ways of finding a load.

#1 rule is to listen to the gun. If it's shooting lights out with N550, stick with it.

Try the audette ladder test to find your charge weight. It tells you a lot more about what pressure your gun likes vs looking at velocities.

When I find two loads which vary very little in velocity on my chrono, the ladder test will reflect it. I'll find two bullet holes next to each other with little vertical dispersion on target. The advantage to the ladder test is that you get visible confirmation and you don't need to rely on a chrono which could be giving you the wrong reading. A chrono that's giving you a reading + - 10fps will be enough to away your opinion on which load is best.