Distance between nodes

[tisme]

I know it all depends on what cal etc but as a rough guide how far apart are nodes in powder? I ask as I've just had a .260 rem built and on testing found a node at 42 grains this was good but I wanted it a little faster the next time the grouping came together was at 42.9 grains. This was sooner than I expected.
Just got me thinking on tuning up some other rifles/loads I have that previously I tough would be over the safe load before a node appeared

 

[Drop Port]

Unfortunately you can't put a number on it, you just have to work up and try to find it and hope you don't hit pressure first. My 6.5x47L hit its upper node 2 grains above the first one and I was able to go 1/2 grain higher with no sign of pressure. My 338 Norma has a sweet spot of over a full grain with very little change.

 

[Shortround]

While I have no scientific basis for proof, I've found that a node comes in about every 3% of powder charge change. Also, at about every 1.5% change will be a scatter node. Further compounding the equation, is that both nodes can be narrow or wide and on the order of 1 - 2%.

I think I first saw the harmonic/wave theory from reading some of Chris Long's theory. That lead to reading Dan Newberry's write ups on OCW (Optimal Charge Weight) and also further refinement with the articles by Donovan Moran. A good site is Practical Riflery.

Going thru all of that will burn up a lot of ammo.

My process is to look at different load data for the cartridge I'm shooting AND the base characteristics of the rifle.
I select powder based on burn rate, my barrel length, and what weight bullet.
Nosler has good charts showing the most accurate load for a given bullet weight and powder charge. Also use any other published info you have to compare.
Shoot a ladder to establish plateau's. 300 to 400 yds is great if you have the range.
Pick the shots with the least vertical.
Load 3 rounds of each load within the plateau range you selected with each load approximately .75 - 1% apart. Shoot a round robin and select the load with the least amount of vertical AND point of impact shift.
Refine further with seating depth changes.

As an example, my Tikka T3 in .223 had overlapping nodes. I was shooting 75 gr Hornady HPBT's on top of 2000MR with a .2 gr separation in charge weight. The first node came in at 25.2 - 25.6 grains and the next node at 26.0 - 26.4 gr. The middle of each group was 3% difference. Verticals were less than 1/4" on both sets. I settled in on the one I wanted and adjusted seating depth.

As such, that little skinny barrel Tikka will shoot .4 moa at 300 yds. At 26.2 grains, I'm less that 1% under the max published with no signs of pressure in my combination of brass, primers, and seating depth. Your results may vary.

I may have been a bit windy, but this works well for me.

Shortround out.

 

[skiutah02]

+1

 

[tisme]

Thanks for the info I'll go out and retest a couple of rifles and see if I can safely find a higher node.
Cheers