Case Fill Percentage / Burn Rate Relationship

[Shooter Mike]

As you get to know me you'll realize I have a special knack for overcomplicating things, and my ability to jump feet first in rabbit holes is unlike any others, and I can never leave good enough and well enough alone.

So I've got a 7 PRC load worked up that I'm happy with. 175gr Berger EH on 63.8gr N560 at 3.361 COAL in Peterson Brass. 2802fps with 6.3SD in 10 shots and 0.34" Mean Radius groups.

I was reviewing the load data and it shows that 66.5gr is 95% case fill. I spent an embarrassing amount of time trying to remember how to figure out what percentage of case fill would 63.8 be .... so I solved for "X" and I did it without google, lol- 63.8 is 91% case fill. As I understand things, 90-100% is recommended. What I'm curious about is, when using a faster powder for a particular caliber, would a case fill in the lower end of that range "generally" be preferred as bullet weight increases? So lets say I try 162gr bullets ... my way of thinking is, with N560 I'd maybe want to be in the 95% range???? But lets say I use H1000 and 175gr bullets, maybe I'd want to be close to 100% case fill, since it's a slower powder?

The 7 PRC is only the second bolt gun I've reloaded for, with the other being a 7mm-08. Everything else has been semi-auto in the 4 years I've been reloading. I want to experiment more with different powders/bullet weights, but I also want to have a logical approach to how I go about it, so that I can better understand why I get whatever the results may be. So this where I start to overcomplicate things, and make it more difficult than it probable needs to be. Thanks!

 

[A382DWDZQ]

QuickLOAD Ballistic Software | QuickLOAD Database for PC

QuickLOAD Software for Windows PC ✔ Ballistic Quickload reloading software → Version 3.9 requires Windows XP or newer OS ✔ ballistic Software and Ballistic calculator.

quickload.co.uk

 

[Shooter Mike]

QuickLOAD Ballistic Software | QuickLOAD Database for PC

QuickLOAD Software for Windows PC ✔ Ballistic Quickload reloading software → Version 3.9 requires Windows XP or newer OS ✔ ballistic Software and Ballistic calculator.

quickload.co.uk

Thanks. I use Mac and don’t own a DVD. I tried parallels and running GRT, and it’s a bit overwhelming- I’m not a tech/computer guy at all.


Sent from my iPhone using Tapatalk

 

[A382DWDZQ]

I see. I run a Mac but use VirtualBox to run windows. I think it is easier than Parallels or any of the options they have. I think QuickLoad is easier than GRT. Just get a USB DVD player. Once you have QL installed you don’t need the DVD to run it. Or pick up a cheap used Dell windows laptop with a DVD drive. I see them on Craigslist for a couple hundred, or Costco.

It’s helpful to be able to tweak settings and view how it affects different things. You can see which powders perform the best at different case fill and volume and % burnt. I don’t think I even scratch the surface of all it can do. It was one of the best reloading investments I have made. Saves me time in trying powders that I can see won’t be ideal.

 

[wind gypsy]

IMO for what you're doing (and basically what near everybody is doing?) it's all noise that doesn't matter unless you are way low on fill % or more compressed than you want to be.

If max charge weight for a given powder leaves you heavily compressed - thats a higher fill % than I'd want. If powder is 1/4 way down the case from the shoulder, it's maybe too low of a fill %. Regardless, there's usually a bunch of powders that fit in the range of "it doesn't matter" for what the fill ratio is.

 

[TaperPin]

As you get to know me you'll realize I have a special knack for overcomplicating things, and my ability to jump feet first in rabbit holes is unlike any others, and I can never leave good enough and well enough alone.

So I've got a 7 PRC load worked up that I'm happy with. 175gr Berger EH on 63.8gr N560 at 3.361 COAL in Peterson Brass. 2802fps with 6.3SD in 10 shots and 0.34" Mean Radius groups.

I was reviewing the load data and it shows that 66.5gr is 95% case fill. I spent an embarrassing amount of time trying to remember how to figure out what percentage of case fill would 63.8 be .... so I solved for "X" and I did it without google, lol- 63.8 is 91% case fill. As I understand things, 90-100% is recommended. What I'm curious about is, when using a faster powder for a particular caliber, would a case fill in the lower end of that range "generally" be preferred as bullet weight increases? So lets say I try 162gr bullets ... my way of thinking is, with N560 I'd maybe want to be in the 95% range???? But lets say I use H1000 and 175gr bullets, maybe I'd want to be close to 100% case fill, since it's a slower powder?

The 7 PRC is only the second bolt gun I've reloaded for, with the other being a 7mm-08. Everything else has been semi-auto in the 4 years I've been reloading. I want to experiment more with different powders/bullet weights, but I also want to have a logical approach to how I go about it, so that I can better understand why I get whatever the results may be. So this where I start to overcomplicate things, and make it more difficult than it probable needs to be. Thanks!

I totally agree with wind gypsy.

Published loads that produce the best, or anywhere near best velocity are automatically in the higher fill side of things. As long as a bullet will seat, the chronograph and target are much more important to worry about.

Also, high fill % don’t always work out well if it’s a struggle to seat the bullet. I’ve had some lots of powder and brass that no way no how would settle enough to get a bullet to stay down with published loads.