Primer pressure signs

Status
Not open for further replies.
K

Kwaynem

Member
Joined
Mar 30, 2019
Messages
177
I’m new so redirect if necessary I loaded some .243 win Winchester brass cci lr primers 42.0 grains of H4350 and had flat primers. I looked at Hodgdon reloading data and it said same load but Winchester LR primers and no flat primers. Round shoots great but worried about the brass I have primed (not loaded) with CCI primers. I’m new to reloading so why does CCI primers show flat primers and Winchester doesn’t?
 
Kwaynem said:
I’m new so redirect if necessary I loaded some .243 win Winchester brass cci lr primers 42.0 grains of H4350 and had flat primers. I looked at Hodgdon reloading data and it said same load but Winchester LR primers and no flat primers. Round shoots great but worried about the brass I have primed (not loaded) with CCI primers. I’m new to reloading so why does CCI primers show flat primers and Winchester doesn’t?
Click to expand...
it's really about how the primer cups some are harder then others. cci look flatter then wins even before you fire. the way the primer ignites the powder makes a difference, referred to hot or cold primers. these can make powder burn faster or slower. i don't think you could get that much h-4350 in the case to be way to hot. photos are very help full. to use. what out side temp did you shoot at.
 
Have a read through this good, visual article. Focus on the section titled "Reading Pressure Signs" The author has shot increasing loads of H4350 and CCI large rifle primers in 6.5 Creedmoor until the point of failure. If you have a magnifying glass or camera with a macro lens, compare your brass to the pictures in the article.

https://www.primalrights.com/library/articles/understanding-pressure

What bullet mass are you using? Is 41gr within the max published loads on Hornady's website, or in your bullet manufacturers load book?
 
Bullet is hornady SST 95 grain .243 Hodgdon website shows 42.0 max load hornady book shows 40.8 max load but I went higher because the groups got better and I wasn’t seeing any over pressure sighns until a friend looked at the primer (CCI) and said it looked flat I’ll post a picture in a little bit
 
I shoot CCI primers exclusively in multiple calibers and they always look flat even in mid range loads. I think trying to read pressure signs via primers is kind of bunk at least with CCI primers. I do look at the primer to see if there is any primer cratering or flow around the firing pin but other then that there most always flat.
 
Muddydogs said:
I shoot CCI primers exclusively in multiple calibers and they always look flat even in mid range loads. I think trying to read pressure signs via primers is kind of bunk at least with CCI primers. I do look at the primer to see if there is any primer cratering or flow around the firing pin but other then that there most always flat.
Click to expand...
I have noticed that also and all I use is CCI in everything. Handgun primers don't seem to do that too bad but LR and SR all flatten out.
 
Once upon a time, I set about to write an article on how much primers flatten vs. pressure. I loaded cartridges from very mild to maximum, fired them, removed the primers, and set them in order from roundest to flattest. There was no correlation between powder charge and flatness. And those were all CCI primers from the same box.

The other pressure signs kick in at roughly 70 KPSI.
 
For that caliber, bullet mass, and powder selection, 42.0 is a maximum load. So I would imagine your COL and trim length would become a bit more critical. Perhaps you loaded it too short, and increased the pressure which was maximum to begin with.
 
If accuracy is good at 42 grs, i would not go higher. Photos look ok.

Watch for loose primer pockets . If pockets get loose at 5 firings or sooner , drop the powder charge.
 
Reading primers can be reliable sign of increasing pressure, not that your load is "safe", or under a certain pressure. Wouldn't be loading a high power rifle cartridge toward the top end without a chrono graph, and comparing the expected velocities. Waiting till you have hard bolt lift or loose primer pockets likely means you are way over design pressure.
 
I’m no expert but those primers seem to have retained some roundness to their edges. But I wouldn’t use a powder charge any greater than the listed maximum. No amount of accuracy is worth it.
 
Status
Not open for further replies.

Similar threads

R
  • Locked
Primer ? for 22-250
Replies
19
Views
3K
jbkebert
J
S
  • Locked
Another Winchester vs CCI SPP question for .357 Magnum loads
Replies
4
Views
757
The Bushmaster
The Bushmaster
R
  • Locked
Primers backing out
Replies
8
Views
734
rec3648
R
N
  • Locked
Small primers for .45ACP
Replies
8
Views
808
jcwit
J
D
  • Locked
CCI Primers - Shotshells
Replies
6
Views
3K
deafsg1
D
Back
Top