Load Density, Bullet Jump, Case Air Space

[Muddyboots]

I know load density and bullet jump has been beaten to death but one issue I cannot resolve completely is how the resulting air space affects burn rate and pressure when a bullet is set against the lands. Or shorter such as SAAMI COAL. The load density is the same but air space can be different which intrigues me. Not sure why but one of those questions you ask yourself eating a Twizzler.

JE Custom once stated the extra oxygen can affect burn rate and that statement has "burned" in my memory for a while and recent loading of the .270TH has me thinking about it again once more. JE also stated bench guys preferred compressed loads for that reason to have consistent burn rates.

Sooo, my far to much time to think mode has me wondering the bullet should be seated at juncture of the powder column of slightly compress instead of trying to seat out against lands. I am shooting the 156HH and I may try some measurements to seat deeper in case and run ladder against previous results of stretching them out to max COAL.

Try this or go back to Twizzlers?

 

[asd9055]

I know load density and bullet jump has been beaten to death but one issue I cannot resolve completely is how the resulting air space affects burn rate and pressure when a bullet is set against the lands. Or shorter such as SAAMI COAL. The load density is the same but air space can be different which intrigues me. Not sure why but one of those questions you ask yourself eating a Twizzler.

JE Custom once stated the extra oxygen can affect burn rate and that statement has "burned" in my memory for a while and recent loading of the .270TH has me thinking about it again once more. JE also stated bench guys preferred compressed loads for that reason to have consistent burn rates.

Sooo, my far to much time to think mode has me wondering the bullet should be seated at juncture of the powder column of slightly compress instead of trying to seat out against lands. I am shooting the 156HH and I may try some measurements to seat deeper in case and run ladder against previous results of stretching them out to max COAL.

Try this or go back to Twizzlers?

Twizlers tast better. The deeper you seat with the same load, the higher the pressure. I sat a bullet once 0.09 deeper than then "normal" ones I was shooting and locked my bolt ( I was not thinking things out at the time). I would say, If you try this, don't be near max.
Also, by definition, the deeper you seat, the higher the load density for same grains of powder!

 

[Mikecr]

The load density is the same but air space can be different which intrigues me.

No, the load density is not the same.
With lower load densities the burn becomes a bit more abstract, which affects results.

If you would like to directly observe this:
-Load 2 rounds at ~85% load density
-Load one with the gun pointed down, slowly raise to level, and fire at target or across a chronograph.
-Load second with the gun pointed up, slowly lower to level, and fire.
-Note the MV or POI difference.
You might also cause the same affect based on how fast/hard or slow/easy you chamber your rounds.

A high load density is not sensitive to these things.

 

[Jud96]

A lot of people believe compressed loads are better and more consistent than non compressed loads. In my opinion, experience, and observations, I don't think it makes a difference unless you're running a load that's like 75% load density or something really light. In my personal .308 Norma my go to load with a 215gr Berger is using RL26 that's about a 90% load density. It shoot extremely well and I don't think shooting a slower power to get more load density could improve on it. Also, the benchrest and F-Class guys often shoot faster powders like H4350 in SAUM/WSM cases because the powder is just so accurate and consistent for them. H4350 in a 300 WSM isn't a compressed load, yet it hammers for those guys.

 

[Muddyboots]

No, the load density is not the same.
With lower load densities the burn becomes a bit more abstract, which affects results.

The bullet seating depth does not change the load density, only the effects of seating depth to powder and pressure. I was wondering how it may affect a load I have that is maxed out COAL with a 156HH in my .270 with RL26 and if I might experiment trying to seat bullets more closely aligned to the powder column instead of the lands. The accuracy is not the issue with the Hammers but seeing if I could improve ES and SD through better powder burn efficiency by better placement of the bullet to the bullet column.

 

[Jud96]

The bullet seating depth does not change the load density, only the effects of seating depth to powder and pressure. I was wondering how it may affect a load I have that is maxed out COAL with a 156HH in my .270 with RL26 and if I might experiment trying to seat bullets more closely aligned to the powder column instead of the lands. The accuracy is not the issue with the Hammers but seeing if I could improve ES and SD through better powder burn efficiency by better placement of the bullet to the bullet column.

I would improve ES and SD but adjusting the powder charge, not the seating depth.

 

[308win]

Only one way to find out....... let us know.

 

[Coyote Shadow Tracker]

Only one way to find out....... let us know.

Packing a load or leaving a load light with a lot of space effects how the powder gasses expand after igniting that's why they have limits for every powder in every cartridge, This also greatly effects the weight and diameter of the bullet. One thing I can say DON"T mess with posted loads for a specific cartridge. You may end up making a Three finger Wildcat Cartridge.
Just saying from experience
"Three Finger Len"

 

[MagnumManiac]

Packing scheme plays a huge role in consistent charges.
If you look at a partially filled case like this, you will see why the air gap is not wanted, sometimes it is unavoidable, but if you think of a cartridge like a popcorn kettle when they blow air in it to mix the popcorn with the butter and salt, the more space there is, the more aerated it becomes.
The primer ignition pressure does the same thing when there is an air gap, the powder is forced away from the flash hole.
Poor ignition can result because the primer flash doesn't enter the powder column, it gets blown through the loose kernels and doesn't ignite as many kernels as the heat is transferred into air and not powder.
This is why in overbore (for want of a better description) cases like the 264WM work best, and produce better curves under MAP when extremely slow bulky powders are used. Even with Retumbo, there is still some space above the powder column.
In these instances, a FCD (factory crimp die) approach can help with ignition by delaying bullet movement momentarily allowing the burning powder to ignite properly before the bullet is released gaining a proper curve under MAP.
A flash over is when there is so much air space that ignition fizzles and the bullet moves but stops, but then ignites again and causes a pressure spike. Seen it myself in a Marlin 1895 45-70 where H4895 left unburnt powder everywhere but caused the lever to lock up. Only part of the powder ignited, even with a crimp.
Anyway, there is more to this, types of powder also contribute to this.

Cheers.

 

[can1010]

quickload now has hammer bullets so I did a quick comparison hope it helps answer your question.
this is generic data not load data.
270 win. RL 26 156 hammers

OAL 3.340
usable capacity 55.7gr
fill ratio 100%
pressure 58737
velocity 3009

OAL 3.600
usable capacity 59.7
fill ratio 93.4
pressure 50306
velocity 2907

now if your touching the lands at 3.6 OAL the pressure jumps to 64086 psi and velocity to 3016

remember this is generic data it is just to show the changes by changing seating depth and if it is touching the lands.
it doesn't change powder density but it changes fill ratio which some might call load density

 

[orkan]

Packing scheme plays a huge role in consistent charges.

^ Huge reason why I run a Prometheus right here. All the benefits of a straight drop out of a measure with a drop tube, with to-the-kernel charge uniformity. I also try to run as close to 100% case fill as I can get. That's where I see my best results.

 

[Chas1]

No, the load density is not the same.
With lower load densities the burn becomes a bit more abstract, which affects results.

If you would like to directly observe this:
-Load 2 rounds at ~85% load density
-Load one with the gun pointed down, slowly raise to level, and fire at target or across a chronograph.
-Load second with the gun pointed up, slowly lower to level, and fire.
-Note the MV or POI difference.
You might also cause the same affect based on how fast/hard or slow/easy you chamber your rounds.

A high load density is not sensitive to these things.

I've tried this and it's true. For me my MV did change but, didn't pay attention to POI, although I sure it changed since MV did.

 

[Muddyboots]

My thoughts go with my specific build which has 0.290 freebore added plus I have max 3.65 COAL which I have been seating at 3.63 for feed purposes. So even at 3.63 I have about 0.030 jump. With RL26 I was getting max vel of 3276 and dropped back even further than I started to 3200 just for brass life. No pressure signs at all at 3200. Lengthy thread on this. Which got me thinking of the air space I might have with this COAL at 3.63 and effects on ES SD. ES ok but not really down near 15 or so where I like to be. I liked seeing the load density numbers from Quick load so I may just drop another grain and seat deeper by 0.010 for couple different loads to try.
Or may just go back to Twizzlers.

 

[SFMongo]

I know load density and bullet jump has been beaten to death but one issue I cannot resolve completely is how the resulting air space affects burn rate and pressure when a bullet is set against the lands. Or shorter such as SAAMI COAL. The load density is the same but air space can be different which intrigues me. Not sure why but one of those questions you ask yourself eating a Twizzler.

JE Custom once stated the extra oxygen can affect burn rate and that statement has "burned" in my memory for a while and recent loading of the .270TH has me thinking about it again once more. JE also stated bench guys preferred compressed loads for that reason to have consistent burn rates.

Sooo, my far to much time to think mode has me wondering the bullet should be seated at juncture of the powder column of slightly compress instead of trying to seat out against lands. I am shooting the 156HH and I may try some measurements to seat deeper in case and run ladder against previous results of stretching them out to max COAL.

Try this or go back to Twizzlers?

The Hornady Manual has a very good article on this in their reloading book.