Pancakes, Craters & Swipes

[Grumpy old man]

Hi all,

Looking at some of my fired cases and wondered about the symptoms of pressure and the order they follow. It would seem that you would get primer flattening (pancaking) first, craters second and case head swipes third along the increasing pressure continuum. Is this correct? If one has pancaking in the absence of heavy bolt lift and other symptoms, is that OK? Here is a picture of a case head from my .25-06. A 52.3 H4831 charge pushing a 117 Sierra. Is this too hot?

View attachment 501279

**** near close to it !

 

[Grumpy old man]

**** near close to it !

 

[YZ-80]

Thank you all for the replies. Very enlightening. Any info that keeps me from blowing the right half of my face off or destroying my rifle is helpful!

 

[YZ-80]

As a rule…honestly I'm still amazed "they" even let us do this sort of stuff unregulated, it's all so subjective and guesswork.

But I've had factory ammo on more than one occasion give a shiny mark on the case head and pancaked primers are perfectly common. I really don't believe it was running 70+ kpsi but I could be wrong of course.

I think Factory stuff is pretty hot. I kind of wonder why? Pressure is also seating depth dependent (right)? I wonder how much "slop" there is in production rifle throat lengths to accommodate the use of all kinds of different production ammo? I suppose the SAMMI specs take this into account.

 

[Mikecr]

I agree with MagnumManiac in that it's hard to make broad declarations for signs with multiple potential causes.

 

[Shane Lindsey]

Looks like ejector print to me. Definitely at the top end.

 

[Mikecr]

Or a sharp edge of the ejector hole in the bolt face.
The fattening primer due to high head space.
The slight cratering due to pin hole fit.
Popping extraction could be present with low breech support or bad bolt timing.
Purely difficult bolt turn could result from oil in the chamber.
Pockets could quickly loosen due to weak brass alloy or excess web clearances.

Every bit of it could happen at a moderate pressure, depending on the ammo and gun build.
You really can't estimate pressures without confirmation from a chronograph.
This is where you see a [pressure sign].

What we can see easy enough is [problems brought on with rising pressure].
And they should be addressed.
But they're usually below an actual [pressure problem].

I could build a gun and ammo to shoot 10Kpsi above SAAMI max, as normal, with no apparent problems.
All I need for this is to address the list above.
I would know fairly well that I'm 10Kpsi high thanks to my chronograph and QuickLoad calibrated to the load.
PressureTrace works even better for this, but you still need the chrono.

 

[Calvin45]

Hey while this thread is still rolling…do nickel plated cases hide pressure signs more? Or exhibit them quicker? Or does it not really matter? I do load some nickel but not a ton and what I have hasn't seen enough firings or hot loads to really tell me much either way

My suspicion is it should mask the appearance of any work hardening and resist shiny marks on the case head (and not just because the whole thing is shiny to begin with, nickel is hard)

 

[Tiny Tim]

My suspicion is it should mask the appearance of any work hardening and resist shiny marks on the case head (and not just because the whole thing is shiny to begin with, nickel is hard)

Great question. I've always wondered if it grips the chamber walls the same as raw brass, or if its harder/slipperier, putting more force on the face of the case head?

 

[YZ-80]

Looks like ejector print to me. Definitely at the top end.

View attachment 501521

I don't know you guys. Good input and thanks. More info on the load. It's running 3070 fps. Would hate to have to back it off. No heavy bolt lift but as some of you know Coopers are stiff to cock anyways.

 

[MagnumManiac]

Hi all,

Looking at some of my fired cases and wondered about the symptoms of pressure and the order they follow. It would seem that you would get primer flattening (pancaking) first, craters second and case head swipes third along the increasing pressure continuum. Is this correct? If one has pancaking in the absence of heavy bolt lift and other symptoms, is that OK? Here is a picture of a case head from my .25-06. A 52.3 H4831 charge pushing a 117 Sierra. Is this too hot?

View attachment 501279

I have to say that many of my own 25-06 cases using either Fed215's or WLRM primers look exactly the same as these and have been run over the Pressure Trace and are safely inside of max pressure.
Here's 2 examples with the primers mentioned. Oh, my chamber is exactly .002" above minimum chamber spec using a RCBS Precision Mic, in fact this is where all of my '06 cases are set, avoids case head separation in the long run…

Cheers.

 

[MagnumManiac]

I have been using ADG brass in my 30 Nosler and I noticed on the third loads when speeds reached 3153 on 205 Berger's I had swipes on a beam scale at 85.4. On the fourth loads using a RCBS LOADMASTER the loads stating on the crono had the speeds from 3137 to 3153 with several showing swipes at the highest end. The ADG brass is supposed to be harder?? But I didn't feel heavy bolt lift or crater pancake of the primers? I'm going to try the straw mod on the Loadmaster and I've ordered a cheap digital scale to recheck the powder being dispensed. I'm going to take the loads down to 85.2. If pressure can be happening before swipes appear then I'm want to be cautious. What have others experienced using ADG brass and swipes? Would this be a true pressure sign?

I see nobody answered your question.
The fact is, brass gets HARDER the more times you shoot it until it becomes 'seasoned', so it no longer expands the same, this can and does cause pressures to rise, meaning what was safe is no longer safe because the brass has nowhere to go, it then gets swipes, if you go further, you WILL get hard bolt lift…
Annealing is the best way to stop this with load reduction…

Cheers.

 

[Calvin45]

I don't know you guys. Good input and thanks. More info on the load. It's running 3070 fps. Would hate to have to back it off. No heavy bolt lift but as some of you know Coopers are stiff to cock anyways.
View attachment 501736View attachment 501737View attachment 501738

Leave that load alone and put it to use! Stack that venison!