What is a "Node"?

[Bart B.]

Any shooter will shoot the most accurate load at the highest velocity they can and stay in the pressure range they are willing to accept.

I strongly disagree.

I originally thought that for best accuracy, I must use the slowest powder that load data listed highest muzzle velocities. That was when I was ignorant of the facts regarding pressure curves' effect on velocity and accuracy.

Conversing with people getting best accuracy (national champs, record setters and Sierra Bullets' ballistics technician) revealed one common thing. Use the powder and charge weights that produces best accuracy. Don't get upset if bullets leave 100 fps slower than another will safely produce. Bullets leave the barrel most consistently when pressure curves are all the same shape and start bullets into the rifling such that they're not deformed and unbalanced. Ball powders are notorious for doing that. The slowest powders often produce highest velocities, but typically with greatest spreads.

Rarely, if ever, do bullets winning the race to the target land in the smallest area. When Sierra their made their first hollow point 30 caliber match bullet for the US Army International Rifle Team to use in 300 meter free rifle matches, that 168-gr. bullet shot most accurate from 308 Win cases leaving about 2200 to 2300 fps in 1:11 and 1:12 twist barrels. That load won gold in the Olympics.

 

[jimmymac]

If I may dumb this down for a moment? What is the fastest load development experimental method that will result in a "keeper" load? I have read about the OCW method, Berger seating depth first method, ladder tests, etc.... The kicker is the amount of variables that can be introduced ( primers, powder, cases, bullets, temperature, fouling, reloading variances, etc) I wish that I understood,and could easily use, a fast and repeatable protocol for load development. The method that wasted the least amount of time would be the most interesting to me. I did like the explanation that a "node" may provide some tolerance for a slightly imperfect powder charge, seating depth or other variables.

I'm a new BR shooter, but have been shooting a long time. I don't know anything about nodes and such, but I often found myself in the same boat as you in regards to potentially wasted time during load development. What I needed was a solid and repeatable method.

What changed things for me was reading Tony Boyer's book and the method he employs to develop loads. This approach is geared towards bench shooting but will work with any rifle. I'm not saying this is the best method to use because frankly, I do not know. It is however, quite useful because every shot ends up on the same piece of paper and tells you a story about your load development. I like this method because it provides me instant feedback and eliminates the need for me to write long essays in my log book regarding load development. As long as I save the target, I don't really need to write much of anything in my log book because it's all right in front of me on a single piece of paper.

Below is one of my recent targets when I was developing a load for my PPC. The numbers across the top are powder charges. The numbers on the left represent seating depths from jam to .012" off of jam. When I was all finished up and looked at the target, it told me a story that the gun seemed to like .012 off of jam across a decent powder charge window and if I wanted to do further development beyond this, that was the place to play around.



Like I said...I'm just a new BR guy. I don't have much to offer, but as I read through this thread it seemed to me that no one really answered your question so I gave it a crack. Hope this helps you like it helped me.

Jim

 

[Bart B.]

All those groups are very good.

But knowing that 3-shot groups with a given load spec will vary at least 4X in size across 15 to 20 of them, I would not put much confidence in any one representing what could be counted on across 15 to 20 groups. And the first one shot is rarely the smallest; largest, either, for that matter.

All it takes to see the reality of my reasoning is to look at the top 10 agg's in a benchrest match, then note who shot their smallest and largest group and when in their several 5-shot groups for any rifle type at each range. Sometimes, the smallest single group in the match is not in any aggregate for the top ten.

 

[eric n]

Load Development for Factory Barrels

1. Ensure rifle's ready; barrel 100% free floated clear of fore end.
2. Use bullets with diameter at least .0003" more than barrel groove diameter and weight in upper weight range for barrel twist.
3. Use new cases or full length sized fired ones whose shoulder's are set back .002" and die's neck is .002" smaller than loaded round neck diameter.
4. Use stick powder about 2/3 to 3/4 up speed range of those listed for bullet weight. Charge weights 2/10ths grain spread maximum.
5. Use primers favored by competitive shooters using the same cartridge.
6. Seat bullets so COAL is 1/16" less than magazine length or to have 1/32" jump to rifling for single round loading.
7. Load 2 rounds at starting charge weight listed, then 2 more in 1 grain increments up to maximum. Test these to find two weights safe at upper range.
8. Most folks shoot smaller groups slung up in prone with the rifle resting on bags; one under fore hand and one under stock toe. Shouldered rifles on bags atop benches are not too repeatable from shot to shot.
9. Load 20 rounds of each then test them in 20-shot groups at desired range. Measure extreme spread or calculate mean radius from group center.

If shots start walking in some direction as barrel heats up, fix the rifle or shoot at a slower rate. If you cool the barrel, the odds of the rifle shooting to same point after getting back into the exact same shooting position are slim. Us humans are not 100% repeatable going back into the same shooting position after getting out of it.

Go with most accurate load.

That is pretty much how a few of us developed a load for Sierra's new 155 grain Palma bullet for 308 Win ammo. Several thousand rounds were loaded for its first use in a match wherein everyone shot the same ammo from prone with metallic sights. It shot about 3" or so at 600 yards in a couple dozen rifles with different barrel profiles; as reported by these top ranked competitors. I got razzed a bit having shot the high aggregate score over 4 days shooting 600, 800, 900 and 1000 yards in 15 to 20 shot strings.

If I may ask. What type of conditions do you like to do development in? How do you account for atmospherics and do you adjust your sight to account for condition change?

 

[jimmymac]

All those groups are very good.

But knowing that 3-shot groups with a given load spec will vary at least 4X in size across 15 to 20 of them, I would not put much confidence in any one representing what could be counted on across 15 to 20 groups. And the first one shot is rarely the smallest; largest, either, for that matter.

All it takes to see the reality of my reasoning is to look at the top 10 agg's in a benchrest match, then note who shot their smallest and largest group and when in their several 5-shot groups for any rifle type at each range. Sometimes, the smallest single group in the match is not in any aggregate for the top ten.

I get that. The more groups I shoot, the agg will creep up, up, up. It has no other direction it can go. The only reason I showed the target to begin with was to provide CTK a methodology that should help in load development.

Since we are discussing that target though, the grand agg of all groups excluding the sighter is less than .2". I was encouraged so I went at it again with minor tweaking and ended up with very similar results.




Powder charges of 28.2 on the left and 28.5 on the right. Seating depth of .010, .012 and .014 off of jam from bottom to top. I'm satisfied. I don't know what else I can really do at this point because I think I might be at the edge of my personal abilities. The gun wants to shoot small over a decent charge window and seating depth window. The only remaining step for me is to shoot 5 shot groups and see if I get similar results. If the results are favorable, I have my load.

Sorry to get off the node discussion guys. I steered this thing in a completely different direction trying to assist CTK.

 

[Toby Bradshaw]

Sorry to get off the node discussion guys. I steered this thing in a completely different direction trying to assist CTK.

Don't apologize. Yours is the most useful information provided in this whole thread. Well done.

I do recommend that when shooting these "Boyer tests" that you use a target page that lets you more easily judge the relative vertical placement of the groups, because finding a seating depth that makes the vertical placement of the group minimally sensitive to charge weight is another part of the load evaluation. You could measure vertical displacement on your target to do this kind of evaluation, but it is hard to see just by looking at it.

Here's one for my 30BR (H4198 weight in gr, Wilson stem length in inches, 100 yd, 3-shot groups):

 

[Bart B.]

What type of conditions do you like to do development in?

For ammo used at 600 yards and further.... First light before sunrise when the air is still, no mirage and can see the target clearly. Then this is possible with unprepped cases. Shots marked 1 and 2 were first couple from a clean barrel; they leave 15 to 20 fps slower than the others.

45.3 grains of IMR4895, RWS primer, WCC60 match 308 Win case, Sierra 155 HPMK, Kreiger 32" 1:13" .2980"x.3075" barrel, SAAMI spec chamber except for .010" shorter freebore, Paramount action, 3.6 lb. trigger.

Same load in Remington BR cases with Rem 7.5 primers shot as well. Also with Winchester PALMA92 cases. Sometimes used 46 grains of Varget with same accuracy.

 

[Bart B.]

I'm satisfied.

You should be. The .0070" one is .0007" smaller than Mike Stinnett's .0077" 5-shot 100-yard world record. Your stuff's doin' all the right stuff 'cause you did all the right stuff.

Your 5-shot groups may well average 10 to 20 percent bigger. 10-shot ones the same above 5-shot ones

 

[CTK]

I get that. The more groups I shoot, the agg will creep up, up, up. It has no other direction it can go. The only reason I showed the target to begin with was to provide CTK a methodology that should help in load development.

Since we are discussing that target though, the grand agg of all groups excluding the sighter is less than .2". I was encouraged so I went at it again with minor tweaking and ended up with very similar results.

View attachment 1015465


Powder charges of 28.2 on the left and 28.5 on the right. Seating depth of .010, .012 and .014 off of jam from bottom to top. I'm satisfied. I don't know what else I can really do at this point because I think I might be at the edge of my personal abilities. The gun wants to shoot small over a decent charge window and seating depth window. The only remaining step for me is to shoot 5 shot groups and see if I get similar results. If the results are favorable, I have my load.

Sorry to get off the node discussion guys. I steered this thing in a completely different direction trying to assist CTK.

I am absolutely going to use this target grid and methodology. Thanks!

 

[CTK]

Don't apologize. Yours is the most useful information provided in this whole thread. Well done.

I do recommend that when shooting these "Boyer tests" that you use a target page that lets you more easily judge the relative vertical placement of the groups, because finding a seating depth that makes the vertical placement of the group minimally sensitive to charge weight is another part of the load evaluation. You could measure vertical displacement on your target to do this kind of evaluation, but it is hard to see just by looking at it.

Here's one for my 30BR (H4198 weight in gr, Wilson stem length in inches, 100 yd, 3-shot groups):

View attachment 1015475

What is the winner amongst all those fantastic groups?

 

[Colt Carpenter]

I found a website that has small quantities of bullets to use for load development also. Saved me a few bucks getting things figured out. Its www.bulletsamples.store

 

[Bart B.]

I wonder what each load's group size would be if shot two more times.

A test is good if it repeats about the same results. Within 10% for group shooting.

 

[Toby Bradshaw]

What is the winner amongst all those fantastic groups?

It's not the "winner" based on group size that I'm looking for. Four of the groups are in the zeros, and with so few shots they are not statistically different from each other.

The purpose of the test is to look at the overall pattern and choose a load that will be forgiving in terms of variation in powder charge and seating depth.

At the jam length (1.737" on the Wilson stem), you can count the bullet holes regardless of the powder charge. Definitely not competitive.

Moving the bullet deeper into the case (out of the lands) by 0.005" (1.742) doesn't help.

Another 0.005" (1.747) and the groups tighten up. 33.5gr is too light, though, as you can see from the 1/2 bullet hole of vertical. (Yes, 1/2 a bullet hole at 100yd means something if you are familiar with short-range BR precision.) At 34.7gr (previously determined to be a working maximum load) there is obvious potential.

At 1.752 on the Wilson stem (0.015" off the jam, 0.002" into the lands by the Alex Wheeler method), all of the groups are round and well-centered, with no vertical movement of the group center with 1.2gr variation in charge weight. At 34.7gr the bullet holes are "small" and the groups are in the zeros across 0.005" of seating depth.

So, for competition out to 300yd, I used 34.7gr H4198 and a Wilson stem of 1.750. No complaints on performance.

Tony Boyer explains this much better. Every serious shooter should read (and re-read) his book.

Any experienced BR shooter can look at this kind of test and come up with a go-to load in less than 50 shots, at least with any of the cartridges commonly used in the game. Any more "load development" than that is just a waste of barrel life.

Of course, with the 6PPC some within-day tuning at tournaments is the norm, and you have to keep up with the movement of the lands. Tune is more stable and barrel life longer with the 30BR.

 

[terraMODA]

A node is like pulling the trigger in between breaths but for the barrel. It is the stillness point between barrel harmonics, when the barrel whip returns to zero again before starting to whip around again. The trick is to find what combination of things will cause the projectile to exit the barrel at this precise time! That is your node. Look up OBT optimal barrel time. It has found and measured where the accuracy nodes are for different barrel lengths. (Different contoured barrels do not change where the nodes are but widen or narrow the node's width respectively. I have used QuickLoad to SWAG (scientific wild ass guess) what powder charges will put me at or near a node.