Would you say excessive pressure would cause powder marks around the neck and shoulder of a fired case. I have also noticed that the primer is not seated quite as deep a primer in an unfired case. Other than that there is no flowing or bulges or other signs of excessive pressure. Any advice would be appreciated.

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Would you say excessive pressure would cause powder marks around the neck and shoulder of a fired case.

No....It can actually be a lack of pressure causing this.

I am with vapodog on this. It typically happens in conjunction with a loose chamber, such as in hunting rifles. With low pressure the case does not fully expand and you get blowback.

Warrior

If you want to know your Reloads are at a SAFE Pressure, there is always the time-proven, never-fail, always-reliable CHE & PRE Pressure Detection Methods.

Best of luck to you.

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powder marks around the neck and shoulder of a fired case.

I normally do not get that with my 303 Brit - until now. The difference is I only sized half the neck length since that is how deep I seated the bullets. There is no sooting behind the shoulder (I headspace on the shoulder). This was a 'normal' below max load. Primer flattening indicated reasonable pressure (i.e. not too low).

You raise two possible issues - the 'sooting' of the necks / shoulders, and the 'backing out' of your primers.

I agree that the sooted necks would indicate a low pressure load. The backing out of your primers could indicate a headspace issue. A couple of questions:

Is this new brass, or fired? If the latter, was it fired in your rifle?

Are you full length resizing, neck sizing, or partial full length resizing?

What calibre are you finding this with?

The problem is plain and simply low pressure. Low pressure will allow gasses to leak back and put soot on the case and neck and it will also cause primers to back out of the pocket.

It is not a headspace problem.

If you are shooting a gas operated auto loader, it's not an unusual occurance. Some powders will soot more than others depending upon the pressures involved.

I agree with vapodog. What it seems to me that you are experiencing due to low pressures allowing some partially burned kernels of powder to get between the case neck and chamber wall before the case neck fully expands to release the bullet. Then, when the case neck does swell up, it crushes these partially burned powder granules between the brass of the case neck and the steel of the chamber wall in that location. When you extract the case, you see these little hunks of partially burned powder.

If you wre experiencing excessive pressures, you would note two things even before pressures got high enough to damage your rifle. These are "loose" primer pockets-the primer pockets expand to the point that they will no longer hold a primer after several reloads. And it becomes difficult to unlock the bolt after firing. In addition, you might note that the headstamps on the cartridges are being smeared and impressions of the machining marks on the face of the bolt are showing up as markings on the brass of the case heads.

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Low pressure will allow gasses to leak back and put soot on the case and neck and it will also cause primers to back out of the pocket.

Grumulkin, may I ask how this happens? The primer backing out, I mean. This is something I have never experienced (but I have seen it with a rifle with a headspace problem) and I have gone from powderless firings up through pistol powder light charges to rifle powder 'starting' loads and right as far as I dared go with a 303 Brit. I always backed off when the primer started to square off its edges. The only 'sooting' I recall is this recent one and I am quite sure the pressure was not too low - it was a 'hotter' load than the one I usually use but the neck sizing was different and I assumed the neck did not expand that much since the case would have been sealing the chamber.

303guy,

Grumulkin has a valid point. If there is an excessive headspace condition, but not enough pressure to blow the case out to the chamber walls immediately, the primer WILL back out. Given excess headspace and full power loads, the primer will still back out some, but it will be flattened against the breech as the case fills the chamber. If the case had been fired in the same chamber and then neck sized or partial full length sized, inadequate pressure shouldn't allow the primer to back out.

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Originally posted by Rikkie:
303guy,

Grumulkin has a valid point. If there is an excessive headspace condition, but not enough pressure to blow the case out to the chamber walls immediately, the primer WILL back out. Given excess headspace and full power loads, the primer will still back out some, but it will be flattened against the breech as the case fills the chamber. If the case had been fired in the same chamber and then neck sized or partial full length sized, inadequate pressure shouldn't allow the primer to back out.

I am finding this with a .270 Win the brass has been fired in the same rifle. Also the brass was full length sized. The load I am using is damn near the max load for that bullet weight/ powder. I also noticed the shot sounds diffrent from pervious loads it is not as much of a pop as before. Would seating the bullet less possibly correct the issue. Right now they are seated close to the min OAL.

My understanding is that the cartridge is driven forward by the firing pin, pressure builds up, expanding the case to grip the chamber walls, the primer then backs out under pressure, the case then stretches and sets back against the bolt face, re-seating the primer. This is what would have happened to that Lee Enfield with excess head-space, only the case did not set back against the bolt face. So from that, low pressure would leave the case forward, gripped by the chamber walls. But it has never happened to me. But, my Lee Enfield has a tight chamber and I neck size and I lube my cartridges (not that that would prevent case wall grip). But why would not have seen it in my 44 mag and other guns I have reloaded for? One of the guns was a 357 mag carbine with a damaged chamber. Normally, with my loads the case would not even bulge into the gouge in the chamber wall but I would expect that if anything, those cases would tend to stay forward. Also, I suppose, most of my loading was with rimmed cases where the possibility of 'out of spec' cases does not exist.

Just interested!

I tried not seating the bullet as much and the soot on the neck is still there. Could it be the brass or is it most likely the charge.

Sometimes a slow powder will let gas back along
the case neck before the case seals it off.
If it is only on the case neck see how loose
a bullet is in a fired, unsized case.
303 Guy you are 100% right on the motions
of a case when fired.
Take care!

Sorry for the late reply; I was hunting for a week with no internet access.

There are at least three signs of low pressure:

1. A lot of soot in the barrel from unburned powder. To burn completely, smokeless powder has to be burned at an optimum pressure.

2. Soot on the neck and even case body. This is because there isn't enough pressure to seal the case against the walls of the chamber when the cartridge is fired.

3. The primers back out. This isn't intuitive but true. I believe it's because the pressure from the primer is enough to blow it back but the pressure in the cartridge isn't enough to drive it back hard against the bolt face to mash the primer into the pocket. If you want to see that this is true, load some rubber primer powered bullets in a cartridge. Unless you drill out the flash holes to a larger than normal size, the primers will back out of the primer pockets.

303Guy

"My understanding is that the cartridge is driven forward by the firing pin, pressure builds up, expanding the case to grip the chamber walls, the primer then backs out under pressure, the case then stretches and sets back against the bolt face, re-seating the primer."

This most often occurs. However with low pressure loads sometimes the pressure is not enough to push the case head back agains the bolt face. Thus the primer remains protruding. Most often happens with rimless cases or with rimmed cases having headspace issues.

"This is what would have happened to that Lee Enfield with excess head-space, only the case did not set back against the bolt face."

Not necessarily so. It dempnds on how tight the extracor holds the case to the bolt face. If it is a close fit then the rim is actually headspaced by the extractor and the should of the case is blown forward. This is what happens in M98s and why a rifle that "field" guages is acceptable. The case is held back by the extractor.

"So from that, low pressure would leave the case forward, gripped by the chamber walls. But it has never happened to me. But, my Lee Enfield has a tight chamber and I neck size and I lube my cartridges (not that that would prevent case wall grip)."

Probably the exact reasons why you've not seen it in that rifle. The cases are headspaced by the tight fit in the chamber.

"But why would not have seen it in my 44 mag and other guns I have reloaded for?"

The same reasons; headspace is correct or the case is held back by the extractor.

Larry Gibson

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3. The primers back out. This isn't intuitive but true. I believe it's because the pressure from the primer is enough to blow it back but the pressure in the cartridge isn't enough to drive it back hard against the bolt face to mash the primer into the pocket. If you want to see that this is true, load some rubber primer powered bullets in a cartridge. Unless you drill out the flash holes to a larger than normal size, the primers will back out of the primer pockets.

That is exactly what happens It matters not if the rifle in question has excessive headspace or not!

However the cases altered this way do indeed show excessive headspace, because the head-to-shoulder length is shortened by the force of the primer. This is the reason why cast bullet shooters are cautioned to reserve cases fired with cast bullets to refrain from using them with full-power jacketed bullet loads in the future.....

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That is exactly what happens It matters not if the rifle in question has excessive headspace or not!

If there was a tight fit in the chamber, the primer could NOT back out. That only happens if the case to chamber fit is loose and, by definition, that's excess headspace.

A reloader can and should correct fot that sloppy fit by the way he FL sizes his cases.

In my experiments, the force of a primer usually drives common bottle neck cases forward about 1 thou and that's not much!

Straight walled revolver rounds headspace on the rim so they really can't be controlled by sizing. But, if the headspace is sloppy, the primers WILL back out until they hit the recoil plate.

Thanks for that Larry.

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That is exactly what happens. It matters not if the rifle in question has excessive headspace or not!

It's just that I have never experienced it in my guns (or should I say, seen it. Perhaps it is as Jim C. <>< says "If there was a tight fit in the chamber, the primer could NOT back out. That only happens if the case to chamber fit is loose and, by definition, that's excess headspace.

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However the cases altered this way do indeed show excessive headspace, because the head-to-shoulder length is shortened by the force of the primer. This is the reason why cast bullet shooters are cautioned to reserve cases fired with cast bullets to refrain from using them with full-power jacketed bullet loads in the future.....

Now that is something I did not know! Interesting. Thanks for that info!

That 303 that left the primer sticking out was not a light load but not 'heavy' iether. The primer protrusion was pretty much what the excess headspace was. (Which was a lot!) I was surprized that a lubed case would adhere to the chamber walls to that extent and that the case was strong enough to resist failure! The next case did fail. There was no visible sign of a difference of pressure (meaning that the difference was not obvious).

All this goes to show how complex the happenings inside a gun barrel really are!

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However the cases altered this way do indeed show excessive headspace, because the head-to-shoulder length is shortened by the force of the primer. This is the reason why cast bullet shooters are cautioned to reserve cases fired with cast bullets to refrain from using them with full-power jacketed bullet loads in the future.....

That is interesting. Having never used lead bullets except in pistol cartridges, was not aware that cases fired w/lead bullets should not be used for full blown jacketed loads. Had to find out about case shrinkage in the school of hard knocks.

Just the firing pin on my pre-64 Mod. 70 30-06 will drive an unprimed, once fired case forward to produce the .001" excessive headspace. Primer apparently pushes shoulder back another .001-.002". Discovered this while experimenting with very light loads of Unique behind 168 gr. SMK's for paper punching (was getting fantastic 100 yd. accuracy). Had to keep this brass separate because cases developed .002-.003" shoulder setback. These light loads produced black necks.

One other thing that has not been mentioned that causes blowby, even with normal pressure loads, is work hardened brass. Did a lot of case preparation so liked to get max. number of reloads from my competition brass. Did not anneal so used the blackening of case necks and shoulder as a guide for scrapping a batch of brass.

Regards,
hm

Hah ha! You see! Rimmed cases are superior!

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If there was a tight fit in the chamber, the primer could NOT back out. That only happens if the case to chamber fit is loose and, by definition, that's excess headspace.

I do not shoot "crush" fit ammunition. And I would not recommend such as an interference fit will cause feeding and extraction difficulties. Still I am surprised that the case is not being sized a little bit by the firing pin impact.

I have been using lubricated cases in my M1's and M1a's. This practice eliminates case head separations in all except one rifle. Fired primers usually have rounded edges. If the cases are not lubricated, the primers are flat. The best explanation is that the primer backs out first.

I often develop loads with lubricated cases. If and when the primers flatten out, I know that pressures are getting high.

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Originally posted by 303Guy:
Hah ha! You see! Rimmed cases are superior!

Probably so when loading reduced loads.

Regards,
hm

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Fired primers usually have rounded edges. If the cases are not lubricated, the primers are flat. The best explanation is that the primer backs out first.

Interesting! Is that why many folks consider primers to be so unreliable a pressure indicator? I figured that cases set back at a lower pressure level when lubed because they are less likely to bind and then give way suddenly or fail at the expansion ring. I also reason that because the case settles back at lower pressure (i.e. earlier), the bolt face and hence the lugs will undergo less stress than with a dry case that does bind. This because the load is applied slightly more gradually. This means that a lubed case is actually beneficial. But that is just my theory!