Percentage of case fill

[Rflshootr]

Some data list case fill percentage. At what point in the case is considered 100% full?
The body/shoulder junction? Neck/Shoulder junction? Somewhere in between?

 

[dmoran]

The free space / volume area under the bullet.
With that said, it depends how much of the bullet is seated into the case and the volume it consumes to it's location with in the case. Dependent on what powders using and there burn rates, it also can be easy to be at compressed loads (over 100% fill) with slower burning powders.

Hope that helps !!!

 

[RegionRat]

In theory, it represents a point where the base of the bullet exactly sits on the powder column without compressing the powder.

ETA: these are "soft numbers" based on averages and tolerances for powder density as well as internal case volume with a bullet seated at a particular depth. Don't take them as laws of physics, but do take them as a guideline for when you may need to pay attention to seating depth issues associated with compressing the powder.

 

[dcali]

Typically, people consider 100% to be the point at which a bullet can be seated without compression and there is no space left in the case. It’s not an ultra precise measure.

 

[Steve Blair]

Powder bulk density (bd) as cited by the manufacturer or Quickload is bd at rest. Using either a long drop tube or a vibration source can decrease that by ~3-6%, kernel size and shape dependent.

 

[Gargoyle]

I wondered this too. I make it a point to load to the base of the bullet in everything. With extruded kernel powder I will sometimes never achieve the desired velocity, so I switch to ball powder to get more fill.

Years ago I learned to keep the powder full in the case. Keeps the SD low because the powder has no movement inside the case. Try loading some lesser but faster powder in a case. Tip the muzzle to the ground and then back to level and fire. The velocity will be lower than if you point it to the sky and then fire.

 

[Rflshootr]

OK, now since that is established, not considering a doughnut at the bottom of the case neck, is it better performance wise to have a long throat and keep bullets on the heavier side seated in the neck and use more powder to get to max pressure, or a shorter throat with the bullet seated down in the case with less powder to get to the same pressure? It seems like at least barrel life would be extended with the latter.

 

[Gargoyle]

OK, now since that is established, not considering a doughnut at the bottom of the case neck, is it better performance wise to have a long throat and keep bullets on the heavier side seated in the neck and use more powder to get to max pressure, or a shorter throat with the bullet seated down in the case with less powder to get to the same pressure? It seems like at least barrel life would be extended with the latter.

That's another good one I've considered. The longer throat and more case capacity is behind the newer PRC cartridges. I have my 300WM at 300PRC performance with seating longer.

 

[dmoran]

( Click on Image )​

@Rflshootr

Made this illustration to show how seating depth effects case capacity (and other loaded round measurements).

Same charge amount (32.7-grains of RL15) to each scenario, but with a seating depth change of 0.040", yields a variation of 1.2% in Load Density, and by 0.4-tenths of a grain in capacity under the bullet.

..........................................................................................................................................................................................

 

[Rflshootr]

View attachment 1393300

( Click on Image )​

@Rflshootr

Made this illustration to show how seating depth effects case capacity (and other loaded round measurements).

Same charge amount (32.7-grains of RL15) to each scenario, but with a seating depth change of 0.040", yields a variation of 1.2% in Load Density, and by 0.4-tenths of a grain in capacity under the bullet.

..........................................................................................................................................................................................

So, am I thinking correctly that a powder with a larger size kernel would even make those numbers bigger, regardless of the burn rate, and vice versa?
Well on 2nd thought, if the powder charge doesn't change, regardless of the type of powder, then maybe not.

 

[6BRA]

Powder bulk density (bd) as cited by the manufacturer or Quickload is bd at rest. Using either a long drop tube or a vibration source can decrease that by ~3-6%, kernel size and shape dependent.

Vibratory platform? Anyone make an item like this? Something you could pour with drop tube and shake at same time?

 

[Hoot]

Vibratory platform? Anyone make an item like this? Something you could pour with drop tube and shake at same time?

Scientific equipment surplus houses sometimes have them. They're kinda pricey new. A more affordable approach would be to fashion one ala DIY. Buy a cheap (HF) variable speed palm sander and bolt it to the bottom of a card table. You don't want too much excitation. Just a gentle coaxing effect. I charge my case first then perch it on top of a variable electro-pencil, dialed way down, with a rubber pencil eraser stuck onto the point. Works great but ties up your hands.

Hoot

 

[gunsandgunsmithing]

Vibratory platform? Anyone make an item like this? Something you could pour with drop tube and shake at same time?

Electric toothbrush against the case

 

[RegionRat]

So, am I thinking correctly that a powder with a larger size kernel would even make those numbers bigger, regardless of the burn rate, and vice versa?
Well on 2nd thought, if the powder charge doesn't change, regardless of the type of powder, then maybe not.

The style (shape) and size of the kernel affects packing factor. The compound density and the packing factor affect the effective density of the powder.

Packing factor can be affected by techniques and methods like vibration and drop tubes.

If you prep a case so that your bullet of interest can slide with just the slightest friction in the neck, then you can play with a scale and a seating depth gage to study the depth it takes to force a bullet base down onto a powder column.

You can vibrate, tap, twist, and push and get various depths that demonstrate how much the powder column can shift around. It can be a worthwhile study if you are interested in a particular recipe that is important to you.

Keep in mind, there are thresholds where seating bullet down to compress the powder column can start to create issues with seating depths and runout. These issues are in addition issues with internal ballistics. If you try to over compress the powder, the bullet seating depth will vary and can cause even change after storage. Trying to push too hard can also create a runout issue.

The sliding bullet study tells you ahead of time where and when to expect trouble with charge levels. YMMV.

 

[big5ifty]

Vibratory platform? Anyone make an item like this? Something you could pour with drop tube and shake at same time?

There is no need for vibration if the drop tube is long and thin enough.

I've got a 50cm drop tube, internal diameter of 5mm. I found the 5mm size more efficient than something a bit bigger. The smallest practical size is large primer diameter.

It goes from this

to this

That is 105 grains IMR 7977 in a 375 RUM.

This was the test rig, it's using a large pistol primer tube. The current version is using a 50cm aluminium tube with a 5mm internal diameter.

 

[6BRA]

There is no need for vibration if the drop tube is long and thin enough.

I've got a 50cm drop tube, internal diameter of 5mm. I found the 5mm size more efficient than something a bit bigger. The smallest practical size is large primer diameter.

It goes from this

to this

That is 105 grains IMR 7977 in a 375 RUM.

This was the test rig, it's using a large pistol primer tube. The current version is using a 50cm aluminium tube with a 5mm internal diameter.

That's a way to free up a hand. Thanks for posting.

 

[Dimner]

At what point in reloading is a drop tube called for? Maybe that's a subjective question.... I get that.
Would you use one dependent on your case fill percentage, or would you use one when your charge weight is over xx grains? Or is it mostly beneficial with large capacity cases?

@414gates pictures are very convincing, but when does it become most beneficial to employ a drop tube?

 

[RegionRat]

Dimner, if you study those photos, the one with the powder stacked well up into the neck is going to cause some issues when trying to seat a bullet.

The feel is one thing with a flat base, and another with a long boat tail. The use of vibration or a drop tube will often make it much easier to seat without fuss. YMMV

 

[big5ifty]

At what point in reloading is a drop tube called for? Maybe that's a subjective question.... I get that.
Would you use one dependent on your case fill percentage, or would you use one when your charge weight is over xx grains? Or is it mostly beneficial with large capacity cases?

@414gates pictures are very convincing, but when does it become most beneficial to employ a drop tube?

For me, it was just a tool to be able to seat bullets without crushing the powder granules.

The bullets will seat without it.