Does this look like over pressure to you?

[jasnt]

Could you even fit too much trailboss in that case?

[Yondering]

Now, one more bit of information to confuse everyone. The case head expansion was only .0038" on a new, never fired case.

Case head expansion, ejector hole marks, and flat primers can all be a result of excess headspace at reasonable pressure, so it's hard to guess much further with the pictures and detail provided. The same things can also be cause by high pressure, but aren't reliable pressure signs by themselves.

Since you said Trailboss and fireforming with a false shoulder, I'm guessing excess headspace, unless your chamber neck is too tight and actually causing high pressure. The force of the primer igniting is probably defeating your false shoulder, even if headspace is correct when you insert the case in the chamber.

[yorketransport]

Could you even fit too much trailboss in that case?

If you compress it enough you could!

So far everyone has cover all the obvious causes, but overlooked a pretty common issue that causes a lot of “unexplained” pressure problems.

Here’s the last hint: I fired 49 other identical loads and this is the only one that came out like this. Charges were all hand weighed, OAL maintained within .003”, necks turned to the same dimensions and it wasn’t caused by any kind of anomaly with the bullet.

[BULLBLASTER]

Could you even fit too much trailboss in that case?

If you compress it enough you could!

So far everyone has cover all the obvious causes, but overlooked a pretty common issue that causes a lot of “unexplained” pressure problems.

Here’s the last hint: I fired 49 other identical loads and this is the only one that came out like this. Charges were all hand weighed, OAL maintained within .003”, necks turned to the same dimensions and it wasn’t caused by any kind of anomaly with the bullet.

Was it all wet?

Or maybe you just punched the trigger way harder on that one?

[yorketransport]

Was it all wet?

Or maybe you just punched the trigger way harder on that one?

I’m going to call that a win!

I didn’t wipe all the lube off of that case. The chamber pressure was likely only between 35-40K psi, but the case couldn’t grip the chamber walls because of the lube. This causes the case to “slip” towards the bolt face faster, causing the primer to get smashed between the bolt face and the case head, giving the lip on the spent primer.

Normally a mistake like this would cause very heavy bolt lift and a potentially dangerous situation which could damage the action. Since these were such low pressure loads (that’s why I use TrailBoss) even the elevated bolt thrust caused by my mistake was less than what would have been caused by a full pressure load.

I just thought this would be a good example of why primers make poor pressure indicators. I cringe every time I hear somebody suggest that a load is safe just because the primers or bolt lift seem “normal”. Likewise, sometimes a primer says the pressure is too high when really there’s something else going on.

[BULLBLASTER]

Winner winner chicken dinner! What do I win? 

When I’m developing loads for my hunting rifles I like to test wet rounds. Even water on a case will increase the pressure or apparent pressure symptoms.

[Yondering]

I didn’t wipe all the lube off of that case. The chamber pressure was likely only between 35-40K psi, but the case couldn’t grip the chamber walls because of the lube. This causes the case to “slip” towards the bolt face faster, causing the primer to get smashed between the bolt face and the case head, giving the lip on the spent primer.

I don't think that's quite the whole story; if headspace was tight and stayed that way the case wouldn't "slip towards the bolt face". Lube on the case can allow the primer to force the case forward more (i.e. sizing it in the chamber, case lube makes that easier), causing the effect of temporary excess headspace. That is what I described in my post above too, but of course lube can sometimes make the problem worse.

On the other hand, sometimes lube has no effect at all, as I've found a number of times, like in a recent batch of fireforming Grendel brass.

Note that it's primer ignition that I'm saying set your case forward, not impact from the firing pin. It's fairly easy to test the effect of each, and I haven't seen firing pin impact set headspace back significantly.

As a somewhat related observation - I've measured as much as .007" headspace increase in some rounds just from dropping a bolt closed in an AR action, without firing the round. I suspect that primer ignition can produce more force to push a case forward than dropping the bolt...

[yorketransport]

I didn’t wipe all the lube off of that case. The chamber pressure was likely only between 35-40K psi, but the case couldn’t grip the chamber walls because of the lube. This causes the case to “slip” towards the bolt face faster, causing the primer to get smashed between the bolt face and the case head, giving the lip on the spent primer.

I don't think that's quite the whole story; if headspace was tight and stayed that way the case wouldn't "slip towards the bolt face". Lube on the case can allow the primer to force the case forward more (i.e. sizing it in the chamber, case lube makes that easier), causing the effect of temporary excess headspace. That is what I described in my post above too, but of course lube can sometimes make the problem worse.

On the other hand, sometimes lube has no effect at all, as I've found a number of times, like in a recent batch of fireforming Grendel brass.

Note that it's primer ignition that I'm saying set your case forward, not impact from the firing pin. It's fairly easy to test the effect of each, and I haven't seen firing pin impact set headspace back significantly.

As a somewhat related observation - I've measured as much as .007" headspace increase in some rounds just from dropping a bolt closed in an AR action, without firing the round. I suspect that primer ignition can produce more force to push a case forward than dropping the bolt...

Saying that the case slips faster was an incredibly simplified version of what's happening. Cases always move forward to some degree on ignition regardless of headgap (it's not technically headspace when referring to the gap between case head and the bolt face). How quickly they expand to fill the chamber again has a lot to do with peak pressures, friction on the case walls (affected by lube or water in the chamber) and malleability of the brass regardless of headgap. 

The force from a primer going off is very significant. Try taking a fired case and popping the primer out without resizing the brass. Now throw something like a Federal 215 primer in there and fire it in the gun. Even an unsized case that's fit to the chamber will be pushed far enough forward to "crush" the shoulder and cause excessive headgap causing the primer to back out. Brass is really soft and the impact of a 19# firing pin spring followed by the force of a primer going off is more than enough to deform the case. Now take that and compound it even more by making dramatic changes in the case geometry when forming a wildcat and changing case taper, shoulder position and shoulder angle all in one shot and that relatively unsupported case doesn't stand a chance against the firing pin and primer.

Forming 6.5 Badger cases from 7 RUM brass requires at least 4 sizing operations plus fire forming with a crush fit in the chamber to make each case. Messing up one of those sizing operations or getting the crush fit in the chamber wrong results in case separation 1/2" from the case head every time; that's the result of improper headspace (headgap). In this situation (not all) it's lubrication on the exterior of the case that's causing the flattened primers even at low pressures.

[Yondering]

It sounds like you're trying to correct or disagree with me, but you're saying the same things I did. What am I missing? 

[yorketransport]

It sounds like you're trying to correct or disagree with me, but you're saying the same things I did. What am I missing? 

Maybe I miss read your post. I thought you were saying that the oil was allowing the case to be pushed forward under the force of the primer. The oil in the chamber isn’t affecting the forward movement of the brass, it’s affecting the rearward movement.

The primer gets flattened out because of the increased bolt thrust caused by oil in the chamber, not headspace.

[Yondering]

The primer gets flattened out because of the increased bolt thrust caused by oil in the chamber, not headspace.

That is incorrect; I thought we were on the same page there but I guess not. High bolt thrust does not cause flattened primers. Flattened primers in a case like this (when pressure is reasonable) are generally a direct result of excess headspace, regardless whether that headspace was caused by sizing or during firing. If headspace is correct and it doesn't change during firing, you won't get flattened primers irregardless of whether there's oil present or not.

The only affect the case lube has on the primer flattening is allowing the case to be pushed forward more, creating temporary excess headspace. Case lube absolutely allows the case to be pushed forward more by primer force; that's pretty easy to test for yourself as you described above.

The lube can also help prevent case head separation, and bolt thrust could theoretically be increased by up to the total tensile strength of the case walls, but that's only a small percentage of total bolt thrust and is not related to primer flattening.

Primer flattening from headpace is caused by the primer protruding from the case a little bit during ignition and being unsupported at the rear. In this position, it starts to balloon out larger than the primer pocket, and when the case is forced back against the bolt by pressure, the primer gets jammed back into the pocket.

[yorketransport]

The primer gets flattened out because of the increased bolt thrust caused by oil in the chamber, not headspace.

That is incorrect; I thought we were on the same page there but I guess not. High bolt thrust does not cause flattened primers. Flattened primers in a case like this (when pressure is reasonable) are generally a direct result of excess headspace, regardless whether that headspace was caused by sizing or during firing. If headspace is correct and it doesn't change during firing, you won't get flattened primers irregardless of whether there's oil present or not.

The only affect the case lube has on the primer flattening is allowing the case to be pushed forward more, creating temporary excess headspace. Case lube absolutely allows the case to be pushed forward more by primer force; that's pretty easy to test for yourself as you described above.

The lube can also help prevent case head separation, and bolt thrust could theoretically be increased by up to the total tensile strength of the case walls, but that's only a small percentage of total bolt thrust and is not related to primer flattening.

Primer flattening from headpace is caused by the primer protruding from the case a little bit during ignition and being unsupported at the rear. In this position, it starts to balloon out larger than the primer pocket, and when the case is forced back against the bolt by pressure, the primer gets jammed back into the pocket.

We'll agree to disagree on this one. I know folks who're on both sides of the "lubed case" debate and the effects it has on brass. My observations over the years when loading for standard chamberings as well as forming and loading for a wide variety of wildcats don't line up with your experience. My experience does coincide with the experience of many highly regarded smiths and shooters. Of course the same can be said about those who're on your side of the issue as well. I've know very experienced shooters and smiths who follow your line of thinking.

I guess the best thing to do here would be to do some testing! We can set up some standardized procedures in which we'll test 10 cases with no oil, 10 cases with oil in the neck/shoulder area, and then 10 cases with oil on the case body only. All the brass would need to be sized the same to give a consistent crush fit in the chamber. We can collect and compare data, crunch numbers and accept the fact that nothing's been proven either way!

[Yondering]

Yes, like I said, it's pretty easy to test. I've already done it, so I know what the answer is. You're welcome to disagree if you want, but better to find out for yourself, no?

[argie1891]

I am more than a little late to this conversation but I fireform by using 10 to 15 gr. of unique or bullseye and than filling the case with corn meal. holding pretty much straight up and firing. if you dont use the corn meal or some other filler the case will not fill out all the way around.  by not using a bullet the pressure is kept low enough that it wont harm your rifle, but fill out the case. if you dont use enough powder it is easy to note as the case wont be formed and it will take another shot to complete the process.