Flattened primers

[Czhowa]

I've reloaded since day one and as such have never bought a factory round. I tend to buy once fired brass and go from there.
A lot of the brass I get has fairly flattened primers, so much so that if I'd handloaded a round that showed the same pressure signs I'd be backing it off a touch.
Has anyone else found this or am I just being overcautious?

Cheers,

Al

 

[Steff]

Same here. Especially RWS ammo seems to be loaded quite hot.
I assume they stretch it to the legal limits. And they don‘t have to look to case life. If it survives the first firing their job is done.

 

[finnbear270]

Hornady Superformance same.

 

[BLUEROLL]

I believe that you can also get flattened primers from even a mild load if the the cartridge headspace is excessive. From what I understand the primer can be partially pushed out by the pressure whilst the cartridge case is gripping the chamber wall, then as the pressure reduces and case expansion springs back it is also forced rearward squashing the primer against the bolt face.
I questioned it once when getting flat primers from a mild load (according to a manual) in my 243 Steyr Prohunter.

 

[Dalua]

From what I understand the primer can be partially pushed out by the pressure whilst the cartridge case is gripping the chamber wall, then as the pressure reduces and case expansion springs back it is also forced rearward squashing the primer against the bolt face.

My understanding of this sequence is little different, though the result's the same:
1. Primer struck. Case and primer pushed forward.
2. Pressure builds. Case starts to grip chamber walls. Primer pushed back out of pocket onto bolt-face (taking up the headspace, in effect)
3. Pressure heads towards max. More of case-walls gripping chamber, but not the parts approaching the web, where the brass is thicker.
4. Pressure at maximum or so. The web/head area is pushed back against the bolt-face, squishing/flattening the primer largely back into the pocket.

Then, as the pressure drops, the brass springs back - but the case has lengthened to fill the headspace, and the thinning of the case above the web has started...

I think if primers are very flat (or in extreme cases, look like they've been smeared in to the pocket like butter with a knife) in the absence of any headspace problems, then it's likely that there is high pressure, or perhaps soft primers.

 

[Muir]

Factory ammo often flattens primers. Not an issue.~Muir

 

[Smellydog]

Yep, you are worrying to much.
Everything I loaded was loaded until I got flat primers unless, I got good accuracy first and shooting 30wcf.
A flat primer by the way is not a sign of excessive pressure.
A primer that has tried to enter firing pin hole is though. Hard extraction is a reliable sign. If that happens you need to drop the charge a touch.

 

[Steff]

My understanding of this sequence is little different, though the result's the same:
1. Primer struck. Case and primer pushed forward.
2. Pressure builds. Case starts to grip chamber walls. Primer pushed back out of pocket onto bolt-face (taking up the headspace, in effect)
3. Pressure heads towards max. More of case-walls gripping chamber, but not the parts approaching the web, where the brass is thicker.
4. Pressure at maximum or so. The web/head area is pushed back against the bolt-face, squishing/flattening the primer largely back into the pocket.

Then, as the pressure drops, the brass springs back - but the case has lengthened to fill the headspace, and the thinning of the case above the web has started...

I think if primers are very flat (or in extreme cases, look like they've been smeared in to the pocket like butter with a knife) in the absence of any headspace problems, then it's likely that there is high pressure, or perhaps soft primers.

Exactly this.
I had completely oversized some .222 brass the other day to an extent that all cases had a crack just above the web section after firing. That was on their second reload. The whole lot was a case for the bin. And precision was down the drain with an otherwise good load.
The primers looked normal btw.