Flat primers... sign of over pressure

[garandman]

I have often heard this is a sign of overpressure but pretty much every load I've ever run gets flattened primers.

223, 224 Valkyrie, 9 mm, 65 creedmoor, 300 BLK incl. Subs, 308, 338 Norma... about the only one that doesn't is 45/70 with black powder.

I usually start about the midpoint of published powder data and work up to just slightly over max. And the primers almost always get flattened.


ETA: e.g. If powder charge ranges from 23.0 - 25.0 grains, I'll get flattened primers even at 24.0 gr (I never load below the middle of the powder range)

If so is this really a sign of overpressure ?

 

[Longtrain]

It’s a sign IMO, some may say that “those primers are known to be soft, so…”.

In my loading for my Dasher, say using RE-15 and a known bullet, you know what the books and conventional wisdom say when you’re entering the high end.

With that in mind, as you slowly approach that forbidden land, grain by grain and you examine your cases, IMO primer flattening is one of the first signs of pressure. Compare the primers as you increase the charge…they will change in appearance.

Now add in, sticky bolt lift, ejector marks on the case from the brass flowing, or the fatal, can’t get the case in the shell holder, you’ve crossed the line. Every rifle’s over pressure line will vary, hence when everyone states that so-in-so’s loading manual is very mild. They need to publish loads that fit a wide range of rifles, their age, their condition, etc.

As you stated, you’re getting flattened primers with charges over the max, you kinda answered your own question.

 

[garandman]

As you stated, you’re getting flattened primers with charges over the max, you kinda answered your own question.

I get flattenned primers from every load, beginning in the middle of the published load data. NOT just when I exceed the max.

e.g. If powder charge ranges from 23.0 - 25.0 grains, I'll get flattened primers even at 24.0 gr (I never load below the middle of the powder range)

 

[Doom]

Flattened primers are a qualitative form of implying overpressure. It has to have a reference point. I use factory ammunition to gage what might be a flattened primer. I have a number of mid range 223 and 308 loads that show some flattening but no other indications of pressure.

 

[robert8904]

I like to put a little light and magnification on them. If the primer still has a rounded edge, I don't worry too much.

 

[Jager]

As pressure begins to become excessive, flattened primers are one of the first signs that we see. But there are a few things that can make that "read" questionable. Things like a slightly undersized primer cup, which then requires undue force to seat the primer, resulting in a "flattened" primer long before the firing pin ever comes into the picture; or a maladjusted priming tool; or, simply, inexperience in interpreting what a "flattened" primer looks like.

If all your primers in all your loads, in all your guns, truly exhibit flattened primers... something is amiss. I'd look first at your priming tool/process.

Beyond that, jumping blind into the middle of a book charge range is probably not the best practice. I'd recommend going to the bottom of book range - from several different load manuals, find consensus - and load a number of truly mild rounds. See what they look like.

Ultimately, a good chrono would tell you what kind of pressures you're actually running, and whether your primers are an issue or not.

 

[Richard Coody]

Well another thing that can cause flattened primers on perfectly acceptable powder charges is oversizing your brass. Excessive headspace leads to flattened primers. I feel that is why many people see flattened primers on factory ammo.

 

[bugman]

"flat" is a relative term. Here is a photo of a "flat" primer. The next step, after "flat" is usually an ejector mark, and you can see that stamped onto the case to the right. Then, if you are lucky, the primers can blank. after that, it is usually is bad news.
If you are seeing this, and your bolt is sticky upon ejection (with a clean chamber) then back off the charge weight until you get more data.

 

[garandman]

@bugman ...

My primers usually look like the one on the right but don't show any ejector mark...

 

[DaveTooley]

This a general statement but applies most of the time.
Under magnification watch the corners of the primers. Compare fired to unfired primers. As you go up in powder charge you will start to see the corners move to fill the primer pocket. The gap between the flat spot from seating the primer and the outside edge of the pocket will start to close. At that point when the corners start to move you're getting close to exceeding the yield point on most brass. This point can vary slightly depending on primer manufacture. Then the decision is do I go up on the charge a bit more for a hunting round I may only shoot 10 times a year or extend brass life on a rifle I shoot hundreds of rounds through a year.

 

[mongo chicago]

Flat primers alone are not a definite indication. There will/should be other signs also. Extracting problems and other marks on the base. You can also have a perfectly good looking primer and still be seriously overpowered. On the reverse side, you can have all sorts of over pressure signs and still be well in the safe zone. I remember reading a good article with pictures using a 30-06 but can't remember what publishing it was in.

 

[dellet]

Small rifle vs small rifle magnum, Remington 6 1/2 are a famous example of starting to flatten around 40,000psi, I use them in low pressure loads like 22 Hornet for exactly this reason.

Factory ammo, lower than average velocity above and below.

Same box of ammo different rifle



Here’s the real problem, pressure is so low that the case sticks to the chamber wall instead of blowing back to the bolt face, complicated by the shoulder set back too far on factory ammo. Note the protruding primers.

Primers can be an indication of high pressure, but they can also be a false flag.

 

[Hammer101st]

I was getting flattined primers on my hot 243 loads but came to find out later that i was makin them flat from my priming process by putting to much pressure on my seater

 

[MislMan]

Got any pictures of your middle load expended brass? Post a pic or two so we can see and provide better comments.

 

[Oso]

As others have indicated, Pressure signs are subjective. It isn't just a measure of the load being excessively hot, but also the interaction of the cartridge with the chamber.

The Pressure signs resulting from the interaction of the cartridge and the chamber can be from (1) too loose of a fit, as captured by Dellet's post above or (2) too tight a fit (Short chamber). After this initial firing, the case will expand/contract to match the rifle's chamber. In subsequent firings using the fire-formed case with the same load there may no longer be any pressure signs or issues.

There is also the potential pressure spike resulting from a bullet seated/jammed too deeply into the lands.

During load development I am watching for primer flattening... I am initially focused on the shape of the firing pin dimple, which typically transitions from deep and round to shallower as the charge weight increases. To me this is an more observable characteristic that I can readily see while at the range. When I get pressure signs that I would characterize as "premature" (moderate loads) then I start thinking about other potential influences (case dimensions, chamber dimensions, neck tension, bullet seating depth, etc.) After a bit of scrutiny, provided that I think the load is reasonable, I will reload several of the newly 1x fire-formed cases and head back to the range. Afterwards, I compare the original cases (1x fired) to the now 2x fired cases. In most instances the 2x fired cases no longer display any of the pressure signs that showed on the initial 1x firing.

Edit: The discussion is focused on primers... there are other signs to also look for. In conjunction with watching the primer I am also inspecting the case. I am looking for ejector swipe marks, extraction marks, case separation, surface texture of case to see if it has excessive friction/stick in chamber, soot patterns, etc.

 

[garandman]

Got any pictures of your middle load expended brass? Post a pic or two so we can see and provide better comments.

I will check. I deprive/ size pretty quick.

Basically they look like the right hand of the 2 cases picture above.

 

[garandman]

As others have indicated, Pressure signs are subjective. It isn't just a measure of the load being excessively hot, but also the interaction of the cartridge with the chamber.


During load development I am watching for primer flattening... I am initially focused on the shape of the firing pin dimple, which typically transitions from deep and round to shallower as the charge weight increases. To me this is an more observable characteristic that I can readily see while at the range.

This is helpful. They do have that deep round crater

 

[divingin]

I was getting flattined primers on my hot 243 loads but came to find out later that i was makin them flat from my priming process by putting to much pressure on my seater

And you didn't notice prior to firing?

 

[jepp2]

Relying solely on primer face appearance is inadequate for assessing the pressure of your load (IMHO).

Two good links:

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

https://www.shootersforum.com/threads/pressure-signs.58763/


I shoot a lot of 25-06 development loads. The SAAMI max pressure for this cartridge is 65,000 PSI. Much higher than many others. I was shooting some 100 gr bullets one day to find my max load given the rifle, case, powder, bullet etc. As I was working my way up my ladder, the first round of the highest powder charge left at 3600 fps. I know that is well above the SAAMI max. So I stopped and when I returned home, I pulled the rest down. QuickLoad said it would take 76,000 PSI to achieve that velocity. And the primer was still well rounded, no case head flow, bolt lift was light and extraction was perfectly normal. Just saying.

The details below are from the 2'nd link. It is the most complete list of all things that "might" shows signs of high pressure.

Load manuals and experienced reloaders frequently advise working a load up in small charge increments while watching for pressure signs. Many beginners are unaware of all the signs. Below is a partial list of them, along with alternate causes of the same signs where I am aware of them. No one particular sign can be counted on to become apparent in all guns, nor even to be consistent with any particular set of load components. There is also no way to tell which sign will show up first in your gun and with your load and component combination, so you need to learn to watch for them all. The standard recommendation, if you get a clear pressure sign, is to back the charge weight of the load down 5%. In most instances, persistent pressure signs do not occur until your pressures are already well above SAAMI MAP.

1. Case bulging excessively. (This is most often at an unsupported part of the case head.)
2. Case cracks along its side. (May mean excess pressure, but may mean brittle, defective, draw mark scored, or worn out brass.)
3. Case head expansion. (A.k.a., CHE. It most often means pressure too high for the lot of brass used, but an isolated example from a lot may mean nothing, as brass is often imprecise, so CHE can occur at pressures that differ by 2:1 within a brass lot.)
4. Case head separation. (May mean high pressure, but may mean excess headspace or worn out brass.)
5. Case splits in body in fewer than 10 reloads. Back powder charge down at least 2%; 5% if in the first two or three reloads. (May also be due to excess headspace, a once-fired case from another gun that was highly stretched at first firing (use paperclip probe to feel for pressure ring inside case and reject any where you can feel one), or is less commonly due ammonia vapor exposure or to a brass defect in an individual case.)
6. Case mouth split in fewer than 6 reloads. (May mean high pressure or ammonia vapor exposure, but more often simply means case needed neck annealing.)
7. Case mouth split in fewer than 4 reloads (May mean high pressure or ammonia vapor exposure, but more often means case got too hot during annealing.)
8. Case pressure ring expansion (A.k.a., PRE; not much more reliable than case head expansion but may mean pressure is excessive for the particular piece of brass or lot of brass it occurs with. It can, for example, happen with Federal commercial brass, but not with Lapua brass or with military brass at the same pressure.)
9. Case primer pockets getting loose in five reloads or fewer. (This is a version of CHE, but may be apparent earlier in pressure. Lowering charge, as in the introductory paragraph, may fix it. However, if the load seems reasonable or is an old standard, same as in 3 and 8, switching make of brass can fix it.)
10. Case stretching excessively. (This is usually visible as pressure ring area stretching which may be due to excess pressure or to excess headspace. Use a bent paperclip or other probe to feel for thinning at the pressure ring. In rear bolt lug guns, the whole case may lengthen before resizing and be impossible to rechamber without sizing.)
11. Case, extractor or ejector marks on head, especially after increasing powder charge to next higher increment. (Most common in semi-auto rifles, but can happen with any extractor and ejector. May be due to high pressure, bad timing in a semi-auto action, or may be due to an improperly fit extractor standing proud on the bolt face.)
12. Case, won’t fit back into chamber after firing. (May mean high pressure, but can also result from a chamber cut at an angle off the bore axis or by an out-of square bolt face. Test for the latter two possibilities by noting head stamp orientation at firing. If case fits back in at that same orientation but no other, then one of these two conditions obtain.)
13. Gas leak. (See Primer Leaking, below.)
14. Groups start to open up at or beyond a published maximum load.
15. Hard bolt lift. (This often indicates excess pressure, but can also result from only one bolt lug making contact until peak pressure is reached (lugs need lapping).)
16. Incipient case head separation (Starting or partial case head separation or signs of it. Can also be a problem with excess headspace.)
17. Increase in powder charge achieves unexpected velocity. (Average velocity will tend to increase by the same number of feet per second per grain of additional powder over the normal operating pressure range. If your next charge increment fails to produce the expected additional velocity or produces too much additional velocity, pressure may be high. Poor grouping usually accompanies this symptom. It is also caused at reasonable pressures by uneven bolt lug contact (lugs need lapping), in which case still further charge increments go back to producing orderly velocity increases and grouping improves. Suspect this last situation if the charge at which the velocity anomaly occurs is in the middle of a published load range. Otherwise, back the charge off 5% from where the issue started.)
18. Primer blown loose. (Primer falls out when gun is opened; same as loose primer pocket, #9, above.)
19. Primer cratering. (May mean high pressure, or it may mean a worn firing pin or firing pin tunnel, or may mean you have a new production Remington bolt with chamfered firing pin tunnel.)
20. Primer flattening. (May mean high pressure, or may mean long headspace; some loads always make flat primers; softer primer cups (Federal) flatten more easily than harder ones (CCI), so it may mean nothing at all.)
21. Primer mushrooming; i.e., primer cup fills out radius at primer pocket perimeter. (May mean high pressure, or may mean excess headspace.)
22. Primer piercing. (May mean high pressure or may mean incorrect firing pin protrusion or incorrect firing pin nose shape.)
23. Primer leaking gas around edges of primer pocket. (May mean high pressure, may mean loose primer pocket in case, may mean damaged primer was inserted, may mean excessive chamber headspace.)
24. Case, short life - back load off at least 2% (under 10 reloads in non-self-loaders, or under 5 loads total in self-loaders before pressure ring is detected with paperclip probe.)
25. Case, sticky or hard extraction. (Especially in revolvers, this is a positive sign to knock the powder charge down at least 5%. In rifles also look for chamber ringing.)
26. Case, torn or bent rim. (Caused by hard extraction, see #24 & #25, above).
27. Case, primer pocket expanded. (A.k.a., PPE; this is the same, in principle, as #9 above, but can be made apparent by measuring with gauges before primers actually are loose. It is a somewhat more sensitive measure than O.D. CHE measurements.)
28. Primer loose or falls out when opening the action or after seating. (See #9 & #27, above).
29. Case, increase in required trimming frequency. (This refers to a sudden increase in case length growth per load cycle. It is actually a less acute version of #10. It can be caused by excess pressure, but can also be a sign of increasing head space due to some other problem. It is especially common as a pressure sign in lever action guns because the greater span from bolt face to rear lug allows more steel stretch when pressure gets excessive.)
30. Case, increase in apparent headspace. (This means the cases are coming out longer, including between the casehead and shoulder. It can mean bolt lug setback, which is usually an extreme pressure sign. It can also mean a loose barrel or an improperly set up Savage barrel. Whatever the cause, the gun should go straight to the gunsmith for inspection.)
31. Gas or Flame Cutting of revolver top strap. (Can also be due to excessive barrel/cylinder gap that needs correction.)
32. Gas or Flame cutting of rifle bolt face by gas leaks around primer pocket or at bolt face perimeter. (Can also be result of occasional leaks from normal rounds firing, as is observed in many military gun bolts.)
33. Velocity higher than manual maximum load velocity reported for same powder charge and barrel length. (May mean excess pressure or a “fast” barrel, but often is actually a chronograph error due to screens being too close to the muzzle blast, bad lighting conditions (watch for ground reflection), or a low battery. In one instance, though, a fellow loading a .243 Win load in the Speer manual and still one grain below the manual maximum was getting velocity readings 200 fps higher than the manual claimed for the higher maximum load. His single-shot action was also popping open at every shot. With QuickLOAD, we were able to calculate he had about 77,000 psi.)
34. Flash hole diameter growing. (This is a more sensitive version of case head expansion. See #3, #9, and #27, above. It can be checked with pin gauges in the form of numbered drill bits or by special gauge.)

 

[RegionRat]

@garandman how would you characterize your sizing versus your shoulder datum?

Like several of the other posts have described, if there is sometimes a condition where the chamber or sizing creates too much slop, the primer cup can flow in the gap between the case head and bolt face and then the case head comes back and makes it look just like overpressure. But I emphasized sometimes to say it isn't always the reason.

If you like to test, try to take one case with a cycle on it and just neck size it and see if it will chamber. Try that same load with cycles to the point where the shoulder or sizing is tight to close and see if the primer still looks like it flows. When the above condition is to blame, a tight case will not show the primer flow. If you still see the primer edges flow with a tight size on the case, then your investigation eliminates the case size but then needs to continue.