Load density to case capacity to consistent vel, es and sd?

[Muddyboots]

Are there any real good articles that discuss the overall load density and how it impacts consistent velocity, ES, SD relative to the COAL of the round? Load manuals typically have load density next to a specific load with a stated COAL. As we change the COAL, the load density is now changed as well since we may be adding "space" behind the bullet for the increased COAL. The amount of this added space changes the calculation of the potential load density. Over the years I have noticed that in some of my rifles, the closer I got to the lands, accuracy improved but not necessarily the velocity nor ES and SD. At short distances, who cares I guess but at distance this is a problem. Powders and bullets have a magic spot for the burn rate and load density to yield the most efficient burn thus, velocity, ES and SD. I would assume accuracy would follow suit to some degree. So I couldn't sleep last night and this popped up in my head and Dang, sleep was even harder to get to after trying to wrap my head around how to arrive a combination of factors without going through powder.

Or should I have just taken a sleeping pill?

 

[Barrelnut]

I have heard and read 90% or 93% or better. But if you look at some reloading manuals, the most accurate loads are usually at or north of 85%.
For ES/SD though I like to see something 90% or better.

 

[MagnumManiac]

I'll give you a scenario I encountered on a few occasions.
Load density, packing scheme and case volume all play a role in what is not only safe, but also in performance.
I loaded a few test rounds with powder X, went straight from loading bench to shooting bench and fired 10 shot strings of each powder load, got best accuracy half a grain from my manuals max load. Proceeded to load an additional 200 rounds with that load, a couple of weeks passed and I was headed to a match some 4+ hours away.
When I got there, I was able to fire a few sighters prior to the match the following Saturday.
Very first round locked the bolt solid, no amount of bashing was getting the bolt open and I didn't want to break the handle free, so I pulled the barrel, it was hand tight yet I couldn't budge it without a barrel vice and wrench set.
Anyway, when home, I pulled 10 rounds down, the first thing noticed was that the powder was well down the case, well below the shoulder/neck juncture. This was not the case when I dumped the powder from the measure. I dumped a few from the measure and the powder was a good way up the neck.
So, the powder had settled and the air gap had caused a pressure issue. I saw that dumping the powder and using a funnel made the powder settle differently, so I worked back up and discovered by swirling powder into the case and lowering the powder column, I had to drop the charge a full 2 grains to stay in safe pressures.
I have also seen a powder charge in new brass to be perfectly safe, but blow primers in once fired brass, all due to packing scheme and load density.
Hope this helps.

Cheers.

 

[therifleman556]

@MagnumManiac
What cartridge & powder combo was this? I usually pour from the weigh pan to the funnel at an angle to get the swirling effect simply because it gets the powder in the case quicker. The reason I ask I guess is because I'm curious what the relationship is between powder and cartridge. I'm assuming that because once settled your load was approximately 90% that the powder was not the slowest one available for that bullet weight? I'm not driving at any particular point, just trying to see a correlation if there is one.

 

[Greyfox]

While generally start with the intention to develop loads that maximize case capacity and a seating depth that is at least 70% bearing surface contact with jumps in the .010-.030" range, I have had loads that demonstrated excellent precision, latitude, low ES, and target velocity at lower case fills and longer jumps. IMO, while this seems to be the most efficient load approach, it may not always produce the optimum results.

 

[J E Custom]

I have heard and read 90% or 93% or better. But if you look at some reloading manuals, the most accurate loads are usually at or north of 85%.
For ES/SD though I like to see something 90% or better.

Lower densities can produce better groups and maybe SD, but in My experiences, It is because of lower pressures, more complete powder burn and normally faster burning powder. The downside to all of this is lower velocities than needed for long ranges.

For the big magnums, I have found that 98 to 100% case densities using powders that can Approach or meet maximum pressures will normally be the best all round. (Good SDs, good groups at range to be used, and good velocities).

Air space in the case can vary and have an effect on burn rate because of the added oxygen. This one of the reasons that slightly compressed charges are preferred by many long range shooters.

I find it easier to work up accuracy/velocity loads using powders that list the maximum load as compressed and start 2 or 3 grains lower and work up. If it reaches the accuracy node at or near 100% case density,
I am not surprised.

Just my experiences with case densities.

J E CUSTOM

 

[Hawk in WY]

You would enjoy playing with QuickLOAD.

https://en.wikipedia.org/wiki/QuickLOAD

I have found their estimates to be amazingly accurate once you get the burn rate for your lot of powder dialed in.

And if you really want to knock yourself out:

http://www.the-long-family.com/OBT_paper.htm

 

[MagnumManiac]

@MagnumManiac
What cartridge & powder combo was this? I usually pour from the weigh pan to the funnel at an angle to get the swirling effect simply because it gets the powder in the case quicker. The reason I ask I guess is because I'm curious what the relationship is between powder and cartridge. I'm assuming that because once settled your load was approximately 90% that the powder was not the slowest one available for that bullet weight? I'm not driving at any particular point, just trying to see a correlation if there is one.

The 3 cartridges in question are the 300WM, 338 Edge and 338-416 Rigby Improved 40 degree. The powders have all been double base and regarded as very slow burn rate in each cartridge/bullet combo.
The powders are not that slow that an overload is not possible, but I also wouldn't drop charges below 5% of predicted max either. Hang fires are a real danger below 5% of max.
In one instance, I had the pressure trace show 2 maximum pressures. The second one, about 2 inches from the muzzle, was above 100,000psi. Something I had heard of but never encountered. This was with RE33 in the 338-416 and a 300gr Berger OTM. Only powder that did it and only with that bullet.
Obviously I stopped all testing with that combo and went to H50BMG/2218 here.
I use the 'swirl' because the packing scheme is always the same height in the case, and when it is compressed, the pressure on the bullet base is also the same. It has reduced my ES considerably and my SD has been very consistent with this method, single digits are possible with a well tuned load.

Hope this helps and answers your question.

Cheers.

 

[smokey3]

I'll give you a scenario I encountered on a few occasions.
Load density, packing scheme and case volume all play a role in what is not only safe, but also in performance.
I loaded a few test rounds with powder X, went straight from loading bench to shooting bench and fired 10 shot strings of each powder load, got best accuracy half a grain from my manuals max load. Proceeded to load an additional 200 rounds with that load, a couple of weeks passed and I was headed to a match some 4+ hours away.
When I got there, I was able to fire a few sighters prior to the match the following Saturday.
Very first round locked the bolt solid, no amount of bashing was getting the bolt open and I didn't want to break the handle free, so I pulled the barrel, it was hand tight yet I couldn't budge it without a barrel vice and wrench set.
Anyway, when home, I pulled 10 rounds down, the first thing noticed was that the powder was well down the case, well below the shoulder/neck juncture. This was not the case when I dumped the powder from the measure. I dumped a few from the measure and the powder was a good way up the neck.
So, the powder had settled and the air gap had caused a pressure issue. I saw that dumping the powder and using a funnel made the powder settle differently, so I worked back up and discovered by swirling powder into the case and lowering the powder column, I had to drop the charge a full 2 grains to stay in safe pressures.
I have also seen a powder charge in new brass to be perfectly safe, but blow primers in once fired brass, all due to packing scheme and load density.
Hope this helps.

Cheers.

6.5 Guys have a good article on this subject on their YouTube Channel. They experiment with a drop tube and also using any kind of vibratory source to settle the powder. After watching their video, I now load all my cases with powder in a loading tray, and then simply hold the tray on top of my vibrating tumbler for a few seconds, allowing the powder to settle. It works great for me and you can visually watch the powder settle in the cases, thus giving a more consistent density.

 

[smokey3]

Here is a good overview of how some people achieve consistent powder density in their reloading procedures on the 6.5 Guys website. Vibratory tumbler is the way I do it, just hold a reloading tray with cases filled with your weight charge of choice against the tumbler for a few seconds and it will compact very nicely as opposed to not doing anything. http://www.65guys.com/tips-techniques-bullet-seating/

 

[MagnumManiac]

Have tried vibratory methods, some way off mainstream, if you get my drift. Lol.
With the WM, Weatherby cases, I was not able to use a vibrator, the powder would spill over the case mouth, so the long drop tube (first) was used, then swirling the powder into the cases. I find this is better than tapping with a long drop tube and way faster.
For some of my loads in comp, I still just drop straight from my measure, I have quite a few set up and they all measure to +/- .1gr. That's ample for most of my comp shooting, but my 'mile' gun, the 338-416 gets a little more precision with every charge weighed exactly.

Cheers.

 

[Canhunter35]

IME the load density is why certain powders become more popular with certain cartridges. They just provide the right amount of fill

 

[MagnumManiac]

IME the load density is why certain powders become more popular with certain cartridges. They just provide the right amount of fill

I agree 100% with this statement.
For instance, RE25 is much less popular in the 25-06 compared to Retumbo, but I found RE25 far superior even though the load density is about 93-95% of case fill with most bullet lengths. It is at 103% in my COL with a 115gr Berger. Just right it appears.

Cheers.