"Reading" primers for pressure.

[Moose83]

So... how reliable is reading primers as a sign of pressure? I keep reading on here about "flat" primers being a sign of higher pressure, yet other sources I've read indicate that primer condition has no correlation to pressure signs, flattened primers are more of an indication of chamber dimensions (I may be mis remembering this part). Case in point... I loaded 5 rounds of .243 with the 95gr BT starting at 40gr up to 44gr of Accurate 3100. All 5 cases primer condition was identical... flattened. Bolt lift and extraction on all 5 was easy and smooth, but the 44gr load looked like it had a very slight ejector swipes. What says Rokslide? How many of you go by primer condition to gauge pressures?

 

[greyghostnw]

Those primers look far from flat from my house and mine usually look flattish… im 2 tenths in a node below my max…In my pressure testing the case base will have raised plunger marks that first show initial pressure therefore becoming trash as you will never be able to size brass back properly in that state again with headspace gauge and caliper because your reading the raised area and will think your fls die needs adjusting but you never should once your brass has fully expanded in firings.

 

[49ereric]

What he said ^

 

[rickyw]

Yeah those look pretty good

 

[mtnbound]

So... how reliable is reading primers as a sign of pressure? I keep reading on here about "flat" primers being a sign of higher pressure, yet other sources I've read indicate that primer condition has no correlation to pressure signs, flattened primers are more of an indication of chamber dimensions (I may be mis remembering this part). Case in point... I loaded 5 rounds of .243 with the 95gr BT starting at 40gr up to 44gr of Accurate 3100. All 5 cases primer condition was identical... flattened. Bolt lift and extraction on all 5 was easy and smooth, but the 44gr load looked like it had a very slight ejector swipes. What says Rokslide? How many of you go by primer condition to gauge pressures?View attachment 975735

I never rely on just one indicator of possible pressure, and those primers look ok to me.

 

[Backcast88]

I would say those 5 primers are pretty far from flat. When the primer no longer had a rounded edge, that would be flat in my book. This is what I would consider a “flat” primer.

This rifle also had heavy bolt lift but no ejector marker or primer crater. But it’s clearly too hot for this rifle. It was notated in the load book for that rifle and will not be replicated.

As other have said, you can't rely on just 1 indicator of pressure. Your rifle will give you multiple clues of pressure, you just need to be aware what they are for that rifle and adjust accordingly.

For example, it looks like nearly all of those primers have a crater. This can be a sign of pressure. But in this rifle, it just might be one of its quirks. I had a Tikka that would crater primers on just about any load I had. But as powder increased, the warning signs were easy to spot and adjust for to stay below any problems.

 

[5MilesBack]

Pressure signs......blew the primers right out of the brass. UM load. Your primers look totally normal.

 

[Colorado Cowboy]

I have been reloading for 65 years and I have seen my share of flattened primers.
First of all if they are caused by chamber dimensions, then every expended primer will be flat.
Second, flattened primers are just one indicator of excess pressure. Usually the bolt will be harder to lift and the case sometimes will look like its been scratched in the rim where the writing is. It could also show signs of carbon deposits. The primer could also show some metal extruded around where the firing pin hit.

Usually I take the flat primer as a warning first sign of pressure. (Like the yellow light before a traffic signal turns to red). Then I recheck everything, especially the powder charger. A couple of times I have neglected to do this and I have totally blown a primer.....now that gets your attention!!!

 

[JGRaider]

I have been reloading for 65 years and I have seen my share of flattened primers.
First of all if they are caused by chamber dimensions, then every expended primer will be flat.
Second, flattened primers are just one indicator of excess pressure. Usually the bolt will be harder to lift and the case sometimes will look like its been scratched in the rim where the writing is. It could also show signs of carbon deposits. The primer could also show some metal extruded around where the firing pin hit.

Usually I take the flat primer as a warning first sign of pressure. (Like the yellow light before a traffic signal turns to red). Then I recheck everything, especially the powder charger. A couple of times I have neglected to do this and I have totally blown a primer.....now that gets your attention!!!

This.......and get a chronograph, which is the very best indication of pressure.

 

[Kruger60]

Good info here. I usually have heavy bolt lift and ejector marks around the same time that I have flattened primers.

 

[flyfisher117]

This.......and get a chronograph, which is the very best indication of pressure.

What are you seeing/watching on the chronograph that indicates pressure?

 

[Finaddictions]

Flat primers are usually more of an indication of pushing the shoulders to far back when sizing.

When a rifle goes off, the firing pin strike pushes the case all the way forward into the chamber where the shoulders stops the movement. As the pressure builds, the first place any movement happens is the primer begins to back out of the case. As the pressure builds, the case is slammed back onto the primer reseating it. If there’s a lot of space to the rear it allows the primer to expand and flatten before it’s seated back into the case. This is why it’s more indicative of generous headspace than it is pressure.

JG Raider has it completely correct above. Use a chronograph to determine pressure. If you look at reloading data, especially for the exact bullet you are shooting along with the powder you are using, whatever their max speed is, would be showing the top end of pressure. Adjust your expected speeds based on your barrel length versus theirs by adding or subtracting 20-25 fps per barrel inch, and you’ll have a good base line for where top end pressures exist.

Usually when pressure signs do manifest themselves, most loads are well over 70,000 psi. With today’s high quality brass, and hardy actions, lots of people get away with high pressure loads, but you should still be extremely careful when working beyond speeds that correlate to published maximum loads.

 

[Moose83]

Pressure signs......blew the primers right out of the brass. UM load. Your primers look totally normal.
View attachment 975886

I've seen this with this particular rifle ... with norma whitetail factory ammo.

 

[Moose83]

This.......and get a chronograph, which is the very best indication of pressure.

I totally agree that a chronograph is the best way to go. I have a "shooting chrony" that a buddy let me use but it seems to be very inconsistent. I would love to pick up a Garmin, but they are about $800 up here and that kinda money buys me a lot of bullets, primers, and powder

 

[49ereric]

Lots of us have been reloading for decades with no chronograph so it isn’t really needed.
They are very nice I read and if you are hunting taking long distance shots then it would be quite helpful. Just depends on if it is affordable to you, many posters here the price is of no concern but for my woods hunting short shots it just isn't needed.
Just be careful of the entire process but even then we fail at times and get a sticky bolt lift.
Looks to me like you are doing fine with the process.