Gunpowder Analysis 7mm PRC

[wabash503]

RS Nation,

Need to borrow some brain power from you guys. I've purchased a 7 PRC and I'm researching load development...yes I've already read through the threads here and elsewhere. What I've done is take a look at the recommended powders for 160 gr bullets from a few different major manufacturers, and then took a look a published velocity and charge weight spreads (see table below).

Is it a good assumption that lower velocity spreads per grain of powder should produce lower ES and SDs? Thanks for your help!

Wabash

 

[A382DWDZQ]

From that list, just go with RL26, or IMR8133 if you can’t get RL26.

 

[wabash503]

From that list, just go with RL26, or IMR8133 if you can’t get RL26.

Thanks for the input... Any thoughts on the data?

 

[A382DWDZQ]

I would not make the assumption that the lower velocity spread in the data will work out to a lower ES or SD. When I look at which powders I want to start with, I usually look at what the bullet manufacturer recommend if that is available, then what powders seem to be known to perform well. If that information is not available or powder is not an option, then I look at % fill for the powder and % propellant burned and try and use the highest velocity & lowest pressure that has high percentages in both of those. That yields a few powders to try and that seems to work well for me for getting peak performance for a particular load. I would also say that some of the mistakes I made were not paying more attention to quality control on my loads early on, trying to force a combination that had good looking numbers on paper to shoot well, chasing velocity when I had a great load at starting charge, and wasting too many rounds on ladders.

 

[AkMtnRunner]

When I researched load data for the same cartridge and bullet weight before deciding to go to it, RL16 looked promising. I found this site helpful: https://www.xxl-reloading.com/

Particularly with a short barrel, % burnt and velocity looked solid, and I see RL16 for sale everywhere around me.

 

[Sako300]

Get some ADG brass and some H1000

 

[ironworker378]

My 7mmWSM has less case powder capacity but produces higher velocity with a variety of powders, out of a 26"bbl

 

[wabash503]

I would not make the assumption that the lower velocity spread in the data will work out to a lower ES or SD. When I look at which powders I want to start with, I usually look at what the bullet manufacturer recommend if that is available, then what powders seem to be known to perform well. If that information is not available or powder is not an option, then I look at % fill for the powder and % propellant burned and try and use the highest velocity & lowest pressure that has high percentages in both of those. That yields a few powders to try and that seems to work well for me for getting peak performance for a particular load. I would also say that some of the mistakes I made were not paying more attention to quality control on my loads early on, trying to force a combination that had good looking numbers on paper to shoot well, chasing velocity when I had a great load at starting charge, and wasting too many rounds on ladders.

I've done a good bit of what you discussed already. How do you figure out case capacity for a given charge weight though? I understand grains of water volume in the case, and that it can vary somewhat based on the manufacturer, but how do you know what volume 4831sc (for example) will have at 64 grains?

Admittedly, there isn't a lot of consensus on what powders work well with the 160 CX... And on top of that, there's limited availability of RL 26 and others to a lesser extent.

Which is why I started looking closer at these other powders that Hodgdon and Hornady have listed for 7 PRC. I will say that I took another look at the numbers as they are approaching max load, and there is some correlation from what I've seen recommended as working well across the spectrum of bullets available (RL26, H1000, 4831SC), and as they approach max they all have 1.5 gr or smaller increases in charge weight within that final 100 fps.

And I find that interesting because it kind of reversed the trend when looking at the same data for the final 300 fps to the max charge weight.

At any rate, I feel like this narrows down the possibilities and I do appreciate your input.

Wabash

 

[Tahoe1305]

My 7mmWSM has less case powder capacity but produces higher velocity with a variety of powders, out of a 26"bbl

I’d argue very close in capacity loaded a tad long and from what I’ve used RL26 is fastest (I load 65 gr and in 24” I’d be just north of 3000fps).

Assume it will be so in PRC also.

Edit: I didnt see 160g bullets. My data is 175g. At 162g I was at 3150fps and 68g.

 

[wabash503]

I’d argue very close in capacity loaded a tad long and from what I’ve used RL26 is fastest (I load 65 gr and in 24” I’d be just north of 3000fps).

Assume it will be so in PRC also.

Edit: I didnt see 160g bullets. My data is 175g. At 162g I was at 3150fps and 68g.

What 7mm are you shooting?

 

[Tahoe1305]

What 7mm are you shooting?

Wsm. In response to the other gentleman.

It’s nearly identical capacity to PRC, and powders are similar (add 2-3g).