Do nodes get smaller as velocity increases?

[miningshawn]

Trying to confirm an observation. I have been loading .223 and .308 all winter for the shooting season and I am starting to see a trend with Varget. Varget always seems to "like" a full case and works well near or slightly over maximum charge, but...
I typically see 3 possible nodes when working up an OCW. I usually go with the highest velocity. But now I am considering the lower nodes because they seem to have a wider range of stability.
My thoughts are geared toward shooting in different temperatures. I typically start working up for the season in February (20 to 30 degrees when working up, too much colder and I don't trust my groups) and may shoot late in the season near 80 or 90 degrees. This is one of the reasons I stick with Varget.
Keeping all of this in mind should I develop the "widest" node I observe within an OCW test or should I run an OCW mid-season? I am debating developing the wider nodes and considering loading near the bottom.
The current recipe I am using is:
43.4gr Varget
Berger 185gr OTM
Starline brass
CCI-BR2
Necks turned to .003 tension, 2.950 COAL with lands at 2.977
This node is stable from 43.3 to 43.6; but, there is another node I developed from 41.7gr to 42.4. If I developed that and took the (admittedly small) bust in velocity would I have more acceptable results and less deviation during late summer and early fall matches? I do like to work up in the spring and use the same recipe through the entire season.
Thanks in advance for your thoughts and experience.

 

[Dusty Stevens]

If youre asking will your load change from 30degrees to 90 degrees? Yes very much so. No matter which “node” you pick it wont be right when the temp changes no matter what powder you use

 

[AJC]

If i was doing what your trying to accomplish is i would be at the bottom of the widest node knowing it was only going to get warmer during your season. You may get out of bracket and want to test or verify speed with large increases in temperature.

 

[mgunderson]

We tend to think of modes as a response to singular barrel vibrations, but they are a collection of barrel vibrations. Width can be smaller at higher "modes" but the math does not require it. If they get smaller at high speeds they should get larger at slower speeds. Are you getting a full grain + width in the 40.5 grain area?

Fclass? I would be tempted to run a tuner to "adjust".

 

[Ned Ludd]

Shawn - the ~43.4 gr region with 185s is known to be an excellent and very tolerant load. It will generally correspond to somewhere in the 2725 to 2750 fps range with a 30" barrel. However, you will experience velocity excursions with this load (or any other, for that matter) if you try to use it at an ambient temperature dramatically different from that in which it was initially worked up. It's just the name of the game if you live in a region with strong seasonal temperature changes. Simply record velocity/temperature through a shooting season and use the information to adjust charge weight as necessary.

Dropping the velocity of the 43.4 gr load by an additional 100+ fps by going with the lower node is not going to buy you any additional "temperature resistance", and you'll be giving up a significant amount of performance. Powder burn rates are regulated largely by pressure and temperature, and you will find that a graph of velocity versus charge weight is not perfectly linear, especially over a wide range of charge weights. Find the node that corresponds to a pressure slightly below max, with a case fill ratio of something like ~94 to 103%, and load to the center of it. As I mentioned, you will need to test at different temperatures to determine how much the "window" and its centerpoint move during the season. Once you have this information, it's generally a matter of adjusting charge weight by a few tenths as the ambient temperature goes up/down to stay in the middle of the window.

 

[miningshawn]

We tend to think of modes as a response to singular barrel vibrations, but they are a collection of barrel vibrations. Width can be smaller at higher "modes" but the math does not require it. If they get smaller at high speeds they should get larger at slower speeds. Are you getting a full grain + width in the 40.5 grain area?

Fclass? I would be tempted to run a tuner to "adjust".

Thanks! Not shooting F class, but I would if there was an opportunity. I try to reload as if I were. I almost hesitate to mention it is an 18" barrel... Even worse it's an RPR - let the flames begin.
The upper node is 0.4gr wide and the lower is 0.9 wide.
I work 2 weeks on/2weeks off in Alaska. Coming home to Montana and reloading to conditions is really time consuming when I would rather be shooting. That is the reason I am sticking to temperature insensitive powders. My thoughts have been to try the widest node and load to the very bottom to allow a small measure of temp stability and avoid ruining cases or piercing primers.
I haven't gone the tuner route yet, but I have been looking into it when I rebarrel.
Thanks again!

 

[miningshawn]

Shawn - the ~43.4 gr region with 185s is known to be an excellent and very tolerant load. It will generally correspond to somewhere in the 2725 to 2750 fps range with a 30" barrel. However, you will experience velocity excursions with this load (or any other, for that matter) if you try to use it at an ambient temperature dramatically different from that in which it was initially worked up. It's just the name of the game if you live in a region with strong seasonal temperature changes. Simply record velocity/temperature through a shooting season and use the information to adjust charge weight as necessary.

Dropping the velocity of the 43.4 gr load by an additional 100+ fps by going with the lower node is not going to buy you any additional "temperature resistance", and you'll be giving up a significant amount of performance. Powder burn rates are regulated largely by pressure and temperature, and you will find that a graph of velocity versus charge weight is not perfectly linear, especially over a wide range of charge weights. Find the node that corresponds to a pressure slightly below max, with a case fill ratio of something like ~94 to 103%, and load to the center of it. As I mentioned, you will need to test at different temperatures to determine how much the "window" and its centerpoint move during the season. Once you have this information, it's generally a matter of adjusting charge weight by a few tenths as the ambient temperature goes up/down to stay in the middle of the window.

Wow, great answer! This is exactly what I was thinking, but I am trying to avoid reloading mid-season. I typically develop then load 1000 rounds per rifle to get me through the year. Not to mention lot variability although Varget has gotten much better.
I should also mention that I shoot at 2500 feet to 6500 feet elevation, but do all of my development and loading at 5250 (PV=nRT on a very small scale).
From this post I will definitely begin adding temp, altitude, and BP to chrono results. I will also shoot 10 across the chrono through the season each trip home. Maybe gathering enough information to adjust loading for conditions through the season.
Thanks again! Lots of good info in here.

 

[D-4297]

I do shoot F-class , and it's 43.3gr Varget , with a 185gr Berger Hybrid and the 185 Jug . Lapua brass , annealed after every firing . Same load for both , and they work fairly well at 600 yds. out of a Brux 30" . I can shoot it at 1,000 , but the winds at BA can mess with the 185 sometimes . Oh yeah . Same load year around , in Arizona . The load was worked up in June at 105 - 108 temps . Ned Ludd is correct about MV . as mine runs a avg. of 2,740 fps. Don't think temp should be a issue , especially with a shorter barrel . My 1,000 yd. load is 44.1 Varget , with a 200.20x , winter load , and 43.8gr Summer load for the 200gr Hybrid bullets . Fire away...