Pressure signs at slow speeds

[Airw4ves]

Hey all, Im sure pressure signs are asked about ad nauseam. But I am stuck wracking my brain on why I am seeing what Im seeing.

Im loading for a 6 creed, 115dtacs, Alpha (non-OCD) SRP brass, CCI 450’s and H4350. These are being shot through a Zeus Action and 26” 1:7.5 twist barrel. Approx 400rnds down the pipe.
Bullets jumped .02, all brass is once fired, and has been annealed on an AMP. .002 shoulder bump, necks turned to .0135 and primer pockets uniformed.

I have found that regardless of the charge I get varying levels of pressure signs. I see ejector marks on every piece I shoot, and primer cratering on loads as low as 37.6gr
Recently I blew 2 primers at a match, and decided to go back to the drawing board. I cleaned the barrel well (no carbon ring) and restarted load development to see what was the issue. During the testing the barrel was allowed to cool for 5 min between groups, and I began to get sticky bolt lift at 38.2gr The test ranged from 37.0gr to 38.8gr. Speed of the 37.0gr loads were 2848fps, and the 38.8gr loads were and average of 2953fps.

Attached are photos of a 37.0 piece and some of the 38.8 pieces.
Thanks for your help

 

[TheOfficeT-Rex]

Is that OCD alpha brass?

Cratering could be firing pin gap... I'd lean towards headspace being a contributing factor for the ejector marks. How fast are you trying to run it?

 

[Airw4ves]

Is that OCD alpha brass?

Cratering could be firing pin gap... I'd lean towards headspace being a contributing factor for the ejector marks. How fast are you trying to run it?

Non OCD.
Was looking for a forgivable load 2850-2900 range, as Im not terribly concerned about chasing speed. Just want a safe consistent load.

 

[st1650]

Totally anecdotal but a friend of mine had a similar issue.
He’s a very very experienced shooter and machinist.
We rented a reamer for the 7SAW.
I have a Bartlein 5R blank and he simply took a off the shelf Tikka T3 7mm-08 and rechambered to 7SAW.
We both used the same brass, same powder as we did our ladder together. Tried both varget and H4350 and he gets a sticky bolt lift on the low end of the ladder (ie at 41.5 varget) but it’s perfectly fine at 42.5 gr which is a fairly hot load.

My barreled action (defiance anTI) was totally fine at both the low and faster node.

We tried doing the same thing with H4350 and sure enough, he got heavy bolt lift at the lower pressure but perfectly fine at the higher.

It’s alpha brass too so maybe it was just a fluke twice and it’s not the load itself but the brass that is weaker ? But yeah he had to work pretty hard to get the case out. Didn’t blow a primer, just heavy ejector swipe.

The only time I’ve ever seen something like this would be if the powder load was way too low but we’re talking about 1gr below max charge so it shouldn’t show any more pressure sign than at Max charge.

CCI 450s
162 ELD-Ms 30thou off
Brand new Alpha brass on its first firing.

 

[Feniks Technologies]

Grab some Lapua 6cm brass and see if the issue goes away. Maybe even some Hornady.

Report back.

 

[Feniks Technologies]

Also, strip the firing pin and ejector and make sure .002 is enough bump that it’s not too little head space.

 

[supercorndogs]

I was wondering about headspace also. I see a line on one of of those pieces of brass in the spot where CHS usually happens.

 

[PinesAndProjectiles]

What’s your measurement to the shoulder datum on a fired case vs a new or sized case?

 

[secondofangle2]

I thought alpha brass was the cat's ass

 

[PinesAndProjectiles]

I thought alpha brass was the cat's ass

It probably is, but no matter how good it is, if you bump your shoulders too far it’ll fuck it up when you fire those rounds.

 

[Feniks Technologies]

It probably is, but no matter how good it is, if you bump your shoulders too far it’ll fuck it up when you fire those rounds.

Cases sized too small would have to be sized significantly smaller to lessen the case capacity enough to have a high pressure issue. Especially at lower charge weights.

When that much headspace is involved, unless you have a very strong extractor, or somehow the case body is very tight, you’ll usually have light strikes as well.

Case bulging and head separations (along with protruding primers at times), light strikes and such are symptoms of too much headspace.

Usually (almost never) blown primers, and ejector marks are not due to too much headspace. Just not how that dynamic works.

Non OCD alpha brass is hit or miss. And has had issues with being soft.

 

[Airw4ves]

Thanks everyone for the ideas and discussion.

Headspace rechecked and .002 is perfect for resistance free bolt drop. All cases were sized .002 after their first firing, and Im not feeling any divits or hitch internally on the case wall that Id think would warn of a case head seperation. Fireformed size is 1.556 and cases resized to 1.554.

I’ll maybe see what I can find for brass, but it may just be resized 6.5 Creed brass for now. Im in Canada and components are near impossible to find without selling an appendage.

 

[Feniks Technologies]

Thanks everyone for the ideas and discussion.

Headspace rechecked and .002 is perfect for resistance free bolt drop. All cases were sized .002 after their first firing, and Im not feeling any divits or hitch internally on the case wall that Id think would warn of a case head seperation. Fireformed size is 1.556 and cases resized to 1.554.

I’ll maybe see what I can find for brass, but it may just be resized 6.5 Creed brass for now. Im in Canada and components are near impossible to find without selling an appendage.

Any other brass will work. Lapua is just good standard and easy to compare.

If you don’t have issues in a couple firings with the other brass, you’ll have your answer.

 

[Barelstroker]

Thanks everyone for the ideas and discussion.

Headspace rechecked and .002 is perfect for resistance free bolt drop. All cases were sized .002 after their first firing, and Im not feeling any divits or hitch internally on the case wall that Id think would warn of a case head seperation. Fireformed size is 1.556 and cases resized to 1.554.

I’ll maybe see what I can find for brass, but it may just be resized 6.5 Creed brass for now. Im in Canada and components are near impossible to find without selling an appendage.

Have you checked case length?
It may be worth while to trim 0.005 below to ensure the neck isn't being pinched in the lead.

 

[Yondering]

Cases sized too small would have to be sized significantly smaller to lessen the case capacity enough to have a high pressure issue. Especially at lower charge weights.

No, it’s not about capacity. In fact sizing the body smaller (not headspace) creates less peak pressure, as some work goes into expanding the case and it dampens that initial peak. Or, going the opposite direction, neck sizing only usually creates a little more pressure. So in my experience, your correlation is backwards there.

HOWEVER- excessive headspace (and it doesn’t take much) can cause false pressure signs on the case head, specifically ejector marks and swipes. For some reason, that symptom seems more prevalent with milder loads and sometimes goes away as the load’s pressure is increased. I’ve seen this happening with as little as .015” headspace (which actually is more common than people realize when they don’t measure, or measure wrong.)

 

[Yondering]

Thanks everyone for the ideas and discussion.

Headspace rechecked and .002 is perfect for resistance free bolt drop. All cases were sized .002 after their first firing, and Im not feeling any divits or hitch internally on the case wall that Id think would warn of a case head seperation. Fireformed size is 1.556 and cases resized to 1.554.

I’ll maybe see what I can find for brass, but it may just be resized 6.5 Creed brass for now. Im in Canada and components are near impossible to find without selling an appendage.

I know you’ve said .002” headspace several times, but compared to what? How are you measuring it?
If it’s against fired brass, did you remove the primers first?

You might know perfectly well how to do this right, but you didn’t say and I’ve learned not to assume people know this; way too many do it wrong. It does matter, because it would explain Most of your symptoms, or else eliminate a possibility.

If you’re only checking by how the sized brass fits the barrel, you might have some minor differences between the die and chamber, resulting in excess headspace to get it to chamber freely. Most commonly at the neck/shoulder junction. Checking headspace compared to several pieces of brass fired with full power loads (this is important!!) will tell a more complete story.

 

[Feniks Technologies]

No, it’s not about capacity. In fact sizing the body smaller (not headspace) creates less peak pressure, as some work goes into expanding the case and it dampens that initial peak. Or, going the opposite direction, neck sizing only usually creates a little more pressure. So in my experience, your correlation is backwards there.

HOWEVER- excessive headspace (and it doesn’t take much) can cause false pressure signs on the case head, specifically ejector marks and swipes. For some reason, that symptom seems more prevalent with milder loads and sometimes goes away as the load’s pressure is increased. I’ve seen this happening with as little as .015” headspace (which actually is more common than people realize when they don’t measure, or measure wrong.)

I was speaking of sizing the case smaller as in headspace.

Since everyone was jumping on the headspace.

Also, unless your experience includes pressure testing equipment, you’re just guessing.

As well as SAMMI spec allows for pretty close to .015 headspace. So again, unless you’re actually checking the pressure, you’re making fairly bold assumptions.

 

[Feniks Technologies]

I know you’ve said .002” headspace several times, but compared to what? How are you measuring it?
If it’s against fired brass, did you remove the primers first?

You might know perfectly well how to do this right, but you didn’t say and I’ve learned not to assume people know this; way too many do it wrong. It does matter, because it would explain Most of your symptoms, or else eliminate a possibility.

If you’re only checking by how the sized brass fits the barrel, you might have some minor differences between the die and chamber, resulting in excess headspace to get it to chamber freely. Most commonly at the neck/shoulder junction. Checking headspace compared to several pieces of brass fired with full power loads (this is important!!) will tell a more complete story.

He’s already stated that he stripped the bolt down and verified his brass was tight prior to sizing and fits after.

 

[Yondering]

I was speaking of sizing the case smaller as in headspace.

Since everyone was jumping on the headspace.

Also, unless your experience includes pressure testing equipment, you’re just guessing.

As well as SAMMI spec allows for pretty close to .015 headspace. So again, unless you’re actually checking the pressure, you’re making fairly bold assumptions.

No, wrong on both counts.

Try reading my first paragraph again, without the "I'm always right" blinders on please. You can compare the same load sized different ways and look at the average velocity; it doesn't take a genius to figure out the correlation with pressure.

And you completely missed the point about headspace and false pressure signs.

 

[Yondering]

He’s already stated that he stripped the bolt down and verified his brass was tight prior to sizing and fits after.

You really should try reading the entire post before responding. I specifically addressed that method and why it's not ideal.

 

[Feniks Technologies]

No, wrong on both counts.

Try reading my first paragraph again, without the "I'm always right" blinders on please. You can compare the same load sized different ways and look at the average velocity; it doesn't take a genius to figure out the correlation with pressure.

And you completely missed the point about headspace and false pressure signs.

That’s what I thought. You’re yet again just posting to “correct” people.

When I post about pressure and such, it’s not based on looking at brass for “pressure signs.”

Carry on with assumptions and amateur hour looking at brass and chronograph.

 

[Feniks Technologies]

You really should try reading the entire post before responding. I specifically addressed that method and why it's not ideal.

Got it. You’re smarter than Alex Wheeler and a host of others.

It also works completely fine. I’d have to tally the rifles I’ve done this on. But it’s several hundred at this point.

And if you’re doing things properly, you should be doing several other things you haven’t mentioned.

I’ll stop even bothering with you anymore. You clearly have not actually tested your claims more so than sitting at home with a set of calipers.

 

[Yondering]

No, wrong on both counts.


That’s what I thought. You’re yet again just posting to “correct” people.

When I post about pressure and such, it’s not based on looking at brass for “pressure signs.”

Carry on with assumptions and amateur hour looking at brass and chronograph.

Good grief fella. This entire thread is about "pressure signs" on brass. Again, read what I actually wrote, and take note of the part about false pressure signs. Excess headspace does do that, if you don't know it yet, that's your own ignorance.

 

[Yondering]

Got it. You’re smarter than Alex Wheeler and a host of others.

It also works completely fine. I’d have to tally the rifles I’ve done this on. But it’s several hundred at this point.

And if you’re doing things properly, you should be doing several other things you haven’t mentioned.

I’ll stop even bothering with you anymore. You clearly have not actually tested your claims more so than sitting at home with a set of calipers.

Ease up and think about some of this a little more before you run around like this. Your comments to me here are a clear knee-jerk against someone contradicting you and you aren't even considering what was really said; like I said try looking at it without the "I'm always right" blinders.

It is entirely possible to end up with excessive headspace with the method you are championing. And no, I did not go into all the details of how to do it right, nor did I claim to.

 

[Cascade Hemi]

OP, have you tried a different powder? Those are not what I'd consider slow velocities for 115DTAC and H4350. H4831 is a better fit for pushing velocity with DTACs.

 

[TylerN]

I like the recommendation to try different brass and see if the issue goes away. If it does that points to an issue with the brass or sizing.

 

[Airw4ves]

Ease up and think about some of this a little more before you run around like this. Your comments to me here are a clear knee-jerk against someone contradicting you and you aren't even considering what was really said; like I said try looking at it without the "I'm always right" blinders.

It is entirely possible to end up with excessive headspace with the method you are championing. And no, I did not go into all the details of how to do it right, nor did I claim to.

Just as an option to try. What method do you recommend to find proper headspace?

 

[Barelstroker]

Just as an option to try. What method do you recommend to find proper headspace?

From what you've previously stated, it seems like you know how to measure case base to datum. Provided you haven't misread the measurement, I can't see why headspace would be your issue.
Have you checked the sized case length?
Make sure the cases are not too long which could cause the neck to be jammed in the lead or a carbon ring which can form at or before the lead.
From what you explained in your case prep details, you did not mention a check of case length or trim to length in the process.

 

[Yondering]

Just as an option to try. What method do you recommend to find proper headspace?

I suggest the standard method of base to shoulder datum comparison between fired brass and sized brass. With the caveat there of course that the brass should have been fired with full pressure loads, and primers should be removed from the fired brass if the base sits directly on the caliper jaws. I like to use 3-5 pieces of brass at least to make sure they're consistent; if the measurement is not consistent then most likely either the cases need to be annealed, or the load wasn't full pressure and the measurement will be shorter than the true value.

You may likely know how to do this already, but as I said when I first asked, I have learned not to assume so it's worth asking. Also, I don't mean to imply that the method you said you've used (sizing until freely chambering) doesn't work; in fact it usually works fine, but it is possible to run into some weirdness once in a while. For example if the neck/shoulder junction in your barrel is very sharp & well defined, but the die is slightly radiused at the same spot (or the opposite condition at the body/shoulder junction), you can end up with a situation that requires sizing further to get the case to chamber freely. The trouble is that method is a little bit blind because you can't see these issues; actual measurements of the base to shoulder datum before and after sizing will tell you if this is the case, and is really easy to do.

Chances are this would really just rule out one of the possibilities in your case, but it's worth doing so you know for sure.

Also, in case you don't know - these measurements should only be used as a relative measurement with that one comparator tool for that barrel; resist the urge to compare your measured values to other people's values measured with different tools on different barrels. Even if you're using a comparator tool with the same size hole as someone else, just minor differences in the chamfer/radius on the hole edge, or lack of, will change the measurement significantly. More importantly, it's a comparison to your rifle's chamber, not published specs or someone else's barrel.

Hope that helps.

 

[rmfield]

Chiming in late here, but in my experience this is probably an issue with your brass. As I understand it, you did not have this issues with the new brass, but now have issues with once fired brass. I think there is something in your brass prep process that is causing this. Over-annealing and shoulder bump (or lack there of) would be the first things I would check.

There is another way to check your actual head space by the way. Get some brass shim material in sizes .002" to 010". Cut out little discs with a notch for the ejector and place them on your striped down bolt face (hold the rifle vertical so they don't fall out). Now close the bolt on a piece of brass and check for resistance. When you find a shim that starts causing resistance then that is approximately your actual headspace. Obviously, there should be no resistance with no shims installed.

As others here have said, try some new brass again and that should tell you if it is a brass problem or not. This what I would do first.

 

[b6graham]

try lapua or peterson or even hornady brass. i bet the issue goes away

 

[Barelstroker]

try lapua or peterson or even hornady brass. i bet the issue goes away

Why would it go away with different brass?
Lapua is nearly always less volume than other cases. Peterson I can't speak to.

 

[b6graham]

Why would it go away with different brass?
Lapua is nearly always less volume than other cases. Peterson I can't speak to.

non OCD alpha brass

 

[Barelstroker]

non OCD alpha brass

What's non OCD Alpha brass got to do with overpressure signs?

 

[spife7980]

What's non OCD Alpha brass got to do with overpressure signs?

Its soft and pressures out prematurely. Pretty common knowledge for a couple years now.

 

[Barelstroker]

Its soft and pressures out prematurely. Pretty common knowledge for a couple years now.

So the case head is soft?
My annealed brass is very soft & I never get pressure signs. Quite the opposite actually. My soft brass doesn't show pressure signs until the primer pockets are loose.

 

[b6graham]

So the case head is soft?
My annealed brass is very soft & I never get pressure signs. Quite the opposite actually. My soft brass doesn't show pressure signs until the primer pockets are loose.

yes very soft.

several recent threads even. some on rifle blow ups because of it. and several others that have been swept under the rug over the years

 

[Barelstroker]

yes very soft.

several recent threads even. some on rifle blow ups because of it. and several others that have been swept under the rug over the years

Yeah right.
My annealed brass doesn't have a soft case head though.
That's hard to believe though I'm not doubting what you say if there is numerous evidence to suggest this.
To be honest, I'm not surprised. Companies can be slow on the uptake.

 

[Yondering]

When I first started using 6.8 SPC brass I bought a bunch from Nosler that ended up being too soft in the case head. Primer pockets loosening with mild loads, and "pressure signs" way below minimum starting loads.

But I've never seen pressure signs in soft brass go away as the load got hotter, which the OP said he is experiencing. I have seen that with headspace issues though, hence my earlier posts above.

 

[dnchrist]

OP, have you tried a different powder? Those are not what I'd consider slow velocities for 115DTAC and H4350. H4831 is a better fit for pushing velocity with DTACs.

I had the same issues in several guns and went to a slower powder. The gas was trying to eject the round before it had had a chance to shrink back. I was getting very good groups, but it was very hard on brass.