Pancakes, Craters & Swipes

[YZ-80]

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?

 

[Calvin45]

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

Looks fine to me.

 

[Recon$$]

I'd run it if it works and no hard bolt lift.

 

[memtb]

I've seen a lot of factory ammo look similar. I assume that they met SAAMI spec's, so…….let'r rip! memtb

 

[lancetkenyon]

Depends on brass too. Some brass (Nosler and Norma) are notorious for soft heads, and show ejector marks and swipes long before primer flattening, even some moderate loads will show ejector marks.

 

[Calvin45]

I've seen a lot of factory ammo look similar. I assume that they met SAAMI spec's, so…….let'r rip! memtb

Heck I've seen Winchester factory ammo look snappier than this…works great too

 

[YZ-80]

Depends on brass too. Some brass (Nosler and Norma) are notorious for soft heads, and show ejector marks and swipes long before primer flattening, even some moderate loads will show ejector marks.

Good to know. I ran Nosler Brass in a 6.5-284 and wondered why I was getting swipes at what seemed to be moderate charges.

 

[Seabeeken]

Keep in mind, by the time you see swipe and stiff bolt, you are 74,000 psi, give or take a little

 

[YZ-80]

Keep in mind, by the time you see swipe and stiff bolt, you are 74,000 psi, give or take a little

Wow! I think a .243 maxes out at something like 55k? That's a lot of pressure and it must not be a linear increase with incremental increases of charge.

 

[biednick]

Primers are not a good indication of pressure. There's all kinds of variables that can cause a load to appear safe with one primer and overpressure with a different primer. Cup thickness is a big one. Thinner cups will flatten, crater, and blank at lower pressures than thicker cups. Cup hardness is similar, with harder cups flattening, cratering, and blanking at higher pressure than soft cups. The fit between the firing pin and bolt face has a big impact too. Guns with a sloppy fit, as is common with Remington 700s, will crater and blank primers at lower pressures especially with thin or soft primer cups. Some firearms don't maintain pressure on the firing pin after the primer is ignited, which will cause them to crater or blank at lower pressure.

One extreme example is my Freedom Arms 2008 handgun. The hammer rebounds immediately after igniting the primer, which results in the primer being fully unsupported. With CCI 400 primers and a starting load of StaBall 6.5 under 140 grain bullets in 6.5 Creedmoor it would blank primers. With 41s, 450, and 200s (200s require different brass as they're LRPs) I can exceed book max with mild cratering and observe no cratering until I hit about the mid point of the listed data.

As SRP 308 and 6.5 Creedmoor have become more common lots of people have discovered issue with loads that should be perfectly safe when using standard SRPs like 400s in mass produced rifles. Switching to primers with thicker cups like 450s resolves the issue for most people. It tends to be less of an issue with custom actions that are made with tighter tolerances.

Ejector swipes are similar, as different companies use brass of different hardnesses. Heavy bolt lift usually doesn't show up until you're way over pressure.

Velocity is one of the best measurements of pressure you can get without specialized equipment. If you're seeing significantly higher velocity than expected for your load with a particular barrel length you should probably tone it down. Case head expansion is commonly used as a pressure metric, but is only loosely correlated to pressure. If you're really worried about it a strain gauge is the way to go.

 

[Calvin45]

Keep in mind, by the time you see swipe and stiff bolt, you are 74,000 psi, give or take a little

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.

But I agree with your statements overall. The presence of some of the more troubling pressure signs is a clear and definite "NO" to the safety of a load but the absence of them isn't necessarily a clear and definite "YES". More like "probably".

Easy bolt lift and relatively normal looking case heads doesn't necessarily mean you're at or under 65kpsi. But stiff bolt lift and pierced or falling-out-loose primers almost certainly means you're WAY over that.

That being said, I think the OP load is absolutely fine.

Moreover this may be foolish but I've kind of come to a "so what?" place of mind when it comes to whether or not I'm slightly exceeding SAAMI spec pressure IN A MODERN BOLT ACTION RIFLE. lever guns, pumps, "old" bolt guns, semi autos, and anything rear-locking is not in the same category. I almost certainly have and use some loads that are a little "hot". And I honestly feel like so what? If I'm still getting decent brass life regarding primer pockets, checking the fired cases over for excessive stretch both in length and diameter at the web as well as visually inspecting cleaned cases for neck splits and incipient case head separation (which should always be done anyway), the bolt is easily lifted and pulled back with one finger (I always abide by my "one finger rule" when developing loads), and chronographed velocity and calculated energy levels are in keeping with what might be considered the very top end of performance for a given cartridge but not in the "raised eyebrow" territory of what's been previously impossible…well then so what if it's in that 65-75k range?

 

[Calvin45]

Primers are not a good indication of pressure. There's all kinds of variables that can cause a load to appear safe with one primer and overpressure with a different primer. Cup thickness is a big one. Thinner cups will flatten, crater, and blank at lower pressures than thicker cups. Cup hardness is similar, with harder cups flattening, cratering, and blanking at higher pressure than soft cups. The fit between the firing pin and bolt face has a big impact too. Guns with a sloppy fit, as is common with Remington 700s, will crater and blank primers at lower pressures especially with thin or soft primer cups. Some firearms don't maintain pressure on the firing pin after the primer is ignited, which will cause them to crater or blank at lower pressure.

One extreme example is my Freedom Arms 2008 handgun. The hammer rebounds immediately after igniting the primer, which results in the primer being fully unsupported. With CCI 400 primers and a starting load of StaBall 6.5 under 140 grain bullets in 6.5 Creedmoor it would blank primers. With 41s, 450, and 200s (200s require different brass as they're LRPs) I can exceed book max with mild cratering and observe no cratering until I hit about the mid point of the listed data.

As SRP 308 and 6.5 Creedmoor have become more common lots of people have discovered issue with loads that should be perfectly safe when using standard SRPs like 400s in mass produced rifles. Switching to primers with thicker cups like 450s resolves the issue for most people. It tends to be less of an issue with custom actions that are made with tighter tolerances.

Ejector swipes are similar, as different companies use brass of different hardnesses. Heavy bolt lift usually doesn't show up until you're way over pressure.

Velocity is one of the best measurements of pressure you can get without specialized equipment. If you're seeing significantly higher velocity than expected for your load with a particular barrel length you should probably tone it down. Case head expansion is commonly used as a pressure metric, but is only loosely correlated to pressure. If you're really worried about it a strain gauge is the way to go.

Very well said! And yes absolutely i want to
Second the comment that it depends on firearms tolerance AND what brass you're using. Norma makes brass that is excellent in terms of grain structure (and subsequent neck tension consistency) and weight and volume consistency from piece to piece. But it is pretty soft.

I have some properly head stamped Norma .257 weatherby brass as well as resized 264 win mag Winchester brass and 7mm rem mag Peterson brass I use in my vanguard.

If the Norma brass exhibits some traditional pressure signs I honestly don't think much of that on its own. If the Winchester stuff does i watch a little more cautiously. If I got a big shiny ejector mark and a loosened primer pocket on Peterson brass id know I was flirting with disaster.

 

[MagnumManiac]

Keep in mind, by the time you see swipe and stiff bolt, you are 74,000 psi, give or take a little

Not in soft brass it isn't.
Generalisation like this is not helpful, and I am NOT having a go at you, as this is what has been stated by many reloading manuals.
The Pressure Trace tells a very different story regarding pressure and brass…things can happen early well below maximum pressure.

Cheers.

 

[Mcranch]

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?