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Pressure signs - primer flow

Shinbone

I am new to the reloading game. I am currently working up a load for my .264 Win Mag with Retumbo and Barnes TSX 120gn. I have been looking for pressure signs to figure out my max load. So far, bolt lift and primer corners do not show pressure. By that I mean bolt lift is still easy and primer corners are still rounded. But, I think I may be starting to get primer flow around the firing pin, which makes me realize that I may not completely understand what I am looking for when checking for primer flow. Also, I am seeing some slight "swipe" marks on just the firing pins.

How does one "look" for primer flow as a max pressure sign? By sight? By feel? Drag finger across the primer dent feeling for a ridge? Is it a sharp ridge or just any protrusion above the flat surface of the primer? Something else?

Regarding primer flow, what exactly tells me I am at max pressure? If I do detect a small amount of primer flow, but there are no other pressure signs, am I still at a safe working pressure?

Below are a couple of examples. Velocity of the left case was 3359, velocity of the right case was 3497. I am interested in understanding the general principles of reading primers and cases for pressure signs.

 
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If your firing pin hole is sized correctly it’s hard to see cratering(primer flow). To me the better indicator is how flat the primer is, squared edges. Plus look for case head smearing. If you get any of the pressure signs, sticky bolt lift, excessive primer flattening or has head smearing it’s a good idea to re evaluate.

Though if your firing pin hole is a bit over sized it will be easy to see cratering as the primer will try to flow back into that hole.
 
Shinbone said:
I am new to the reloading game. I am currently working up a load for my .264 Win Mag with Retumbo and Barnes TSX 120gn. I have been looking for pressure signs to figure out my max load. So far, bolt lift and primer corners do not show pressure. By that I mean bolt lift is still easy and primer corners are still rounded. But, I think I may be starting to get primer flow around the firing pin, which makes me realize that I may not completely understand what I am looking for when checking for primer flow.

How does one "look" for primer flow as a max pressure sign? By sight? By feel? Drag finger across the primer dent feeling for a ridge? Is it a sharp ridge or just any protrusion above the flat surface of the primer? Something else?

Regarding primer flow, what exactly tells me I am at max pressure? If I do detect a small amount of primer flow, but there are no other pressure signs, am I still at a safe working pressure?
Click to expand...
More often than not, primer cratering is due to improper firing pin fit rather than max pressures. I have a rifle that craters the primers no matter what the load is. Primer flattening is better, but even that depends on the particular primer (some are stronger than others), and can give misleading impressions if headspace is excessive (this allows the primer to push out a little, where it is unsupported, making it easier to flatten). Ejector marks/swipes and bolt stickiness are much better indicators, as a they are measures of permanent brass deformation that can only happen with pressure, but by the time you see that, you’re almost certainly at max pressure. It’s best to keep all of these signs in mind in totality. That, along with the knowledge of where you are charge-wise (from a reloading manual) should give you a decent idea as to how hot you are pushing things. As always, caution is advised.
 
I guess I don't really give a whole to primer cratering or even flat primers because, like has already been mentioned, oversized firing pin holes can give a false reading and sometimes excessive headspace can cause flat primers.

My "go to" pressure signs are listening for a click as you raise the bolt handle, sticky or heavier than normal bolt lift, and ejector swipes. Also, if you are running things across a chronograph, velocities well above normal can be a good indication as well.

Also, be mindful of cartridges with "improved" shoulder angles and minimal case taper because they can often hide pressure signs, which is why I like to use a chronograph whenever possible.
 
Shinbone said:
Regarding primer flow, what exactly tells me I am at max pressure?
Click to expand...
Nothing about primers show max pressure, and pressure 'signs' and actual pressure 'problems' can be independent of published max.

None of us know our actual pressures. All we can do is work up smartly, slowing at signs and stopping at any problem until resolved. That's the local max.
 
I can't really tell but it almost looks like an ejector mark over the "G" on the left case and another between the G and Y for the case on the right. Is the ejector on this gun square by chance? If so, then I'd say those are ejector swipes and you are a bit over max.
 
I'm relatively new to the reloading game (been doing it for 4-5 years). While I'd heard it said in forums that primer flattening is an unreliable indicator of high pressure, someone put it in a way that really resonated with me: The primer doesn't know (or care) what caliber cartridge it is installed in. It's going to take a certain amount of pressure to flatten the primer - totally independent of what the cartridge being fired is. Therefore, one can still have over-pressure for a given cartridge even though the primer isn't flattened.

I concur with the previous comments about bolt force and using a chrono.
 
Looks like you need a new firing pin spring.
Youre not over pressure but you could be real quick this summer. Get a loupe or magnifying glass and look for the ejector
 
Thanks for all the great feedback. Lots of details for me to learn about this pressure stuff. Based on the feedback, I added a few more photos.

I agree with B23 that I think I see square ejector marks in the first photo. But, they sure are hard to see in real life and in these other photos.

And, the close-up of the bolt face shows a small machining "gouge" which appears to correspond to the swipe marks on the primer. In fact, in addition to the wipe mark, the primer is picking up an exact impression of the gouge. Which I guess is an example of primer marks being caused by bolt's physical characteristics/idiosyncrasies rather than caused by over pressure.





 
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Found this list of pressure signs in another thread:

index.php
 
I see a small gouge near the firing pin hole that is engraving into the primer during ignition. A piece of self adhesive 320 grit sandpaper stuck to the head of a spent case, chucked in a drill will work to polish out that defect.

I don't see brass flowing into that big ol' ejector slot, so your load isn't completely over the top. But the primers are flattened and therefore you are near or at max safe load in YOUR chamber. No one else's chamber matters, just yours.

Reading primers is like reading tea leaves. Don't put much faith in it until you know your gun and your loading ability reeeeeeal well. If unsure, back off. And then get yourself a good chronograph. If for instance the book says max is 2800 fps out of a 24 inch barrel, and you're getting 2950 out of a 22 inch barrel, you can be certain that you're well into unknown territory regarding pressure and pretty near to getting your face blown off. When pressures are too great, typically the gun will handle it UNTIL...... the temperature rises well above the day you developed the load. Or you're cleaning process leaves a carbon buildup in the neck/throat. Of you forget to trim the brass back after several firings. Or you switch to a different primer.

Then you pull the trigger on a hot day, with a dirty chamber, and a too long case neck that pinches the bullet in the throat, and suddenly that marginally safe load is now WAY too hot and you quickly find yourself in the big red/white van headed to the hospital.

Keep it safe, for the wife and kids.
 
Interesting question, 243winxb. My numbers seem about 100 fps too fast, to me, too.

I shot two rounds at 69.0 gn of Retumbo, which was my max load for the day. I got 3490 fps and 3497 fps, respectively, with my Labradar. That is out of a 26" Winchester factory barrel.

It is my understand, that with the Labradar, the number it spits out is either spot-on or totally crazy-wrong, so I am not sure what to think.
 
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