Pressure Signs in the 6.5x47

Although there is much to like about the 6.5x47, one aspect does concern me. Cases anecdotally do not show the same evidence of peak pressure that one might see in other designs - particularly large rifle primer designs. Although the similar newer small rifle Creedmore cases may have the same characteristic (as may other similar designs; PPCs, Grendel and the like), I'd like to limit my attention to just the design in the title: the 6.5x47L with Lapua brass.

Published guidelines for load development typically describe loading up incrementally until evidence of peak pressure is noted in causing changes in the case dimensions and/or primer. The symptoms usually referred to are a marked and measurable expansion of the case head just above the extraction groove that necessarily mean primer pockets are stretching, or perhaps stiff extraction. At this point the guideline is usually to back off 1-2 grains and call max load. So far so good.

When I've taken this approach and cross-checked my loads and muzzle velocities against QuickLOAD and also with Pressure Trace equipment, the estimated peak pressure at which the above symptoms have first been observed in large rifle pocket brass has been around 64-66kPSI. Clearly there is variation around the temper of the brass, so only a rough figure.

I'm finding an ever-growing number of reports online saying that 6.5x47 Lapua brass does not seem to show the same developing pattern of signs of increasing pressure as described here: https://www.primalrights.com/library...nding-pressure
or at least if it does the progression is much compressed. Onset of the above indications with bolt lift or pocket expansion may only appear above 70kPSI.

This may seem at first glance to be a good thing; a case designed and manufactured to allow for higher pressure and resulting muzzle velocities, and that holds up at these levels over multiple reloads. The concern is that the ultimate failure point may be at much the same peak pressures as most other case designs, and whereas with these other designs, you as the reloader may be 4-5 grains of powder away from catastrophic case failure when sticky bolt lift is first noted, in the 6.5x47 the margin might be only 1-2 grains. I'm speculating here of course. I've not loaded a 6.5x47 to failure. In fact I've not seen sticky bolt lift or pocket expansion because of my conservative loading brought about by concern over the uncertainty of the above. Maybe the ultimate failure point is also raised proportionally?

But I am interested in hearing from shooters of the 6.5x47 who have seen pressure signs in their rifles.

Could I trouble you please to either reply here, or PM me if you don't want your experiences aired publicly, and let me know what signs of pressure you have seen in this chambering? I would like to put your load details through QuickLOAD to see what the predicted peak pressure comes out as. For this I would need to know the powder that was used and the quantity, the particular bullet, and the cartridge-overall-length, and ideally your crown-to-bolt-face barrel length and muzzle velocity as a first pass way of checking the simulation results. Rifle action type would be helpful if it is thought that it contributed in some way to the symptoms such as a propensity for extractor marks, primer cratering etc.

It may be that the traditional methods of load development are not well suited to the 6.5x47 without resulting in top loads of questionable safety.

First up we have a sticky bolt lift at an estimated peak pressure of 72,700 PSI that does not occur when this is lowered to an estimated 71,300 PSI with no other pressure signs.

If no one ever mentioned pressure then it would be a lot safer. You are just comparing one made up number with another. Pressure is stress.

Brass strain is the result of stress. Too much stress and you get too much strain. If you are not getting brass strain, you are not getting a lot of stress. Pressure creates stress, stress creates strain. Pressure is homogeneous. Stress does not always come from pressure. If the case fails to grip the chamber wall you get massive stress on the bolt lugs without a lot of pressure.

A chronograph tells you more than anything else. You will see max pressure over the chronograph with 6.5x47L before you see any strain, at least with 2209 anyway.

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Originally Posted by Tussock

You will see max pressure over the chronograph with 6.5x47L before you see any strain, at least with 2209 anyway.

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If this was true then it would be commonly known and accepted that load development with the 6.5x47 should be approached differently rather than looking for pressure signs. I have not seen velocities increase with 2209 anything other than in a uniform monotonic way. Please tell us what you know from your experience as you appear to have operated up where things became... interesting?

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Originally Posted by Puffin

If this was true then it would be commonly known and accepted that load development with the 6.5x47 should be approached differently rather than looking for pressure signs. I have not seen velocities increase with 2209 anything other than in a uniform monotonic way. Please tell us what you know from your experience as you appear to have operated up where things became... interesting?

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Nope. Never seen anything interesting. Just saw the velocity gains start to taper off. Were you getting the same gain per increment of powder linearly?

Why do you have no "pressure signs" if you have pressure?

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Originally Posted by Tussock

Nope. Never seen anything interesting. Just saw the velocity gains start to taper off. Were you getting the same gain per increment of powder linearly?

Why do you have no "pressure signs" if you have pressure?

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Yes, no flattening-off of velocity increases with incremental increases in charge weight.

You know very well that in using the term "pressure signs" I am referring to dimensional changes in the case and primer that are commonly used by shooters as an indication that peak pressures on firing have reached levels widely accepted as a limit for safe operation. Rather than being a contrarian are you instead prepared to provide the data where you saw velocity start to taper off so it can be considered as alternative method for load development for this cartridge ?

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Originally Posted by Puffin

Yes, no flattening-off of velocity increases with incremental increases in charge weight.

You know very well that in using the term "pressure signs" I am referring to dimensional changes in the case and primer that are commonly used by shooters as an indication that peak pressures on firing have reached levels widely accepted as a limit for safe operation. Rather than being a contrarian are you instead prepared to provide the data where you saw velocity start to taper off so it can be considered as alternative method for load development for this cartridge ?

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No, I am simply pointing out shooters use "pressure signs" for relative pressure. You are mixing this with absolute pressure. Your "72,000 PSI" has a margin of error of about 10,000psi. When you see case deformation which shooters refer to as "pressure signs" these are not actually pressure signs.

Its just a lack of understanding which fortunately does not seem to matter that much as few people die handloading. It is a dangerous misconception of the relationship of pressure, stress and strain.

If you get case deformation the source may or may not be pressure. It could be you have lubed the inside of your chamber causing excess bolt thrust. It is much safer to be aware case deformation has more sources than pressure.

Its is also safer to be aware of what is happening to the action to create each different type of case deformation. Sticky bolt lift is a different thing to ejector marks. One is chamber expansion and the other is bolt thrust.

There is no reason to care about absolute chamber pressure because you have no way of knowing what it is. The number is completely irrelevant. You can produce dangerous case deformation at very low powder charges in a variety of action/brass combinations. Think of all the people loading random cheap once fired factory brass? What you said about the 6.5x47L is true for all of them. The brass is weaker, so you have no idea where its failure point will be.

If you have no case deformation, no sticky bolt lift or any other form of STRAIN then it is unlikely you need to worry about strain.

My point is you are confusing people in a way that is dangerous. If you want to get all high tech and roll out quickload, then why can't we switch to using the proper language for this?

I am not being contrarian, I am pointing out the conventional language of shooting, while completely functional in a practical sense, can't be used for the kind of theory you have.

Stick with convention. Even though "pressure" is nonsense, those "dimensional changes" used by shooters are all you care about. You start with small ones and you progress to case separation. If they are not there, then you don't have a problem, end of story.

I'm not recommending that shooters disregard actual signs of deformation in their fired cases in favour of theoretically calculated pressure. I am however interested in whether the calculated peak pressures for certain signs of strain that they do see are widely spread or clustered. As I said in my initial post, having assessed my own cases in the past - mainly for case head expansion measurements - I was surprised at how similar the figures were across a variety of cases. Admittedly I had control of a number of variables that could otherwise have caused wider variation. Your figure of error of 10,000PSI may well be correct when these variables are not controlled.

This thread is going to be of interest and read by very few on here anyway. The pool of 6.5x47 shooters here is small. Fewer still have ways of assessing pressure other than with the conventional indications used by reloaders. So far I have a data set of only one.
If you really think that I am confusing people in a way that is dangerous I can take this topic off-line and PM the shooters of this round that I know of directly.

Quote:

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Originally Posted by Puffin

I'm not recommending that shooters disregard actual signs of deformation in their fired cases in favour of theoretically calculated pressure. I am however interested in whether the calculated peak pressures for certain signs of strain that they do see are widely spread or clustered. As I said in my initial post, having assessed my own cases in the past - mainly for case head expansion measurements - I was surprised at how similar the figures were across a variety of cases. Admittedly I had control of a number of variables that could otherwise have caused wider variation. Your figure of error of 10,000PSI may well be correct when these variables are not controlled.

This thread is going to be of interest and read by very few on here anyway. The pool of 6.5x47 shooters here is small. Fewer still have ways of assessing pressure other than with the conventional indications used by reloaders. So far I have a data set of only one.
If you really think that I am confusing people in a way that is dangerous I can take this topic off-line and PM the shooters of this round that I know of directly.

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I'm not singling you out. All I am saying is in terms of safety, you have to go off of the signs of brass deformation. People should not doubt that approach because in terms of stress and strain, it is the only safe one.

I found you don't see any problems until you suddenly really see problems. Hot loads were showing no problems til a warm day and a slight jam in the lands from a walking seater die and whoops extremely sticky bolt lift.

Quote:

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Originally Posted by Puffin

I'm not recommending that shooters disregard actual signs of deformation in their fired cases in favour of theoretically calculated pressure. I am however interested in whether the calculated peak pressures for certain signs of strain that they do see are widely spread or clustered. As I said in my initial post, having assessed my own cases in the past - mainly for case head expansion measurements - I was surprised at how similar the figures were across a variety of cases. Admittedly I had control of a number of variables that could otherwise have caused wider variation. Your figure of error of 10,000PSI may well be correct when these variables are not controlled.

This thread is going to be of interest and read by very few on here anyway. The pool of 6.5x47 shooters here is small. Fewer still have ways of assessing pressure other than with the conventional indications used by reloaders. So far I have a data set of only one.
If you really think that I am confusing people in a way that is dangerous I can take this topic off-line and PM the shooters of this round that I know of directly.

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I think this topic may be of much wider interest than you realise as the availability of Lapua brass for the 6.5 Creedmoor makes this discussion of direct relevance as far as I can tell.

In my 9 months worth of experimentation with the Creedmoor I haven't seen any really obvious signs of pressure in my brass. Then I tried Re26... After a lot of research I decided to try up to a max of 48 grains behind the 143 ELD-X in Lapua brass/CCI450 primer. The top load had some extrusion of the primer in to the firing pin hole. This powder also shot poorly from my rifle so I gave it up totally. So my limited results backs @gimp's experience.

Anyone who has converted Palma brass to 7mm08, 260 or 243 might also want to chime in as well.

I think that unless you're working up in 5 grain increments you're unlikely to go from high pressure but no signs on the brass (safe) to exploding rifle. You just have less warning that you're getting to the top of what the brass will handle.

this thread is very much of interest . . .

I also find this thread of significant interest.

I think your theory is sound. By deferring pressure signs, as I said in another thread "sweeping pressure under the rug" you will compress them into less grains of powder. At the same time, when you get there, the size of the loading increment will give you very little gain. Unless you are a muppet and loading 5gr increments, as Gimp said, then everything should proceed as normal.

Now the point I made was that pressure and powder charge are not actually linked. So the issue here with the highest quality brass in individually machined actions is probably extremely trivial compared to people following the loading book with random brass and questionable rifle tolerances.

So you still have to stick to the one thing you have, which is deformation of the case. The case is the weak link. In 6.5x47L it is a very strong weak link. 6.5x47L is a case built from the ground up by wizards. 6.5 Creedmore is a wildcat given a thickened case base as an afterthought (by the same wizzards).

Mostly these things will be in the hands of people shooting them over chronographs in high end actions where you can get to the scary bit and back off.

Mine were doing 2800 with 140s (don't have the rest of the info on hand) and I have dug out 3 of my >300 3X fired brass and I don't have any case head deformation. As I mentioned in another thread I had ejector marks on one factory loading and completely flattened primers on another, when at the range the other day. Wincherster and Sellior and Belliot. Two different rifles. A Sako and a Ruger.

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Originally Posted by Tussock

I think your theory is sound. By deferring pressure signs, as I said in another thread "sweeping pressure under the rug" you will compress them into less grains of powder. At the same time, when you get there, the size of the loading increment will give you very little gain. Unless you are a muppet and loading 5gr increments, as Gimp said, then everything should proceed as normal.

Now the point I made was that pressure and powder charge are not actually linked. So the issue here with the highest quality brass in individually machined actions is probably extremely trivial compared to people following the loading book with random brass and questionable rifle tolerances.

So you still have to stick to the one thing you have, which is deformation of the case. The case is the weak link. In 6.5x47L it is a very strong weak link. 6.5x47L is a case built from the ground up by wizards. 6.5 Creedmore is a wildcat given a thickened case base as an afterthought (by the same wizzards).

Mostly these things will be in the hands of people shooting them over chronographs in high end actions where you can get to the scary bit and back off.

Mine were doing 2800 with 140s (don't have the rest of the info on hand) and I have dug out 3 of my >300 3X fired brass and I don't have any case head deformation. As I mentioned in another thread I had ejector marks on one factory loading and completely flattened primers on another, when at the range the other day. Wincherster and Sellior and Belliot. Two different rifles. A Sako and a Ruger.

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Does the same not also more or less apply to those chamberings based on the 404 Jeffery. That case was used because it can withstand very high pressure safely.

A second load to consider, and if the information on this was more complete, I'd just report the predicted peak pressure along with the pressure signs as before. However that is not the case so here is the the information on which the simulations were based so the missing information and assumptions are clear.

140gr bullet ( AMAX I think), 20" barrel, likely to be 70.5-72mm CoL but not confirmed, velocity: 2810 ft/sec, showed stiff bolt lift in warm conditions, but not in cold, so clearly right at the cusp.
Powder and charge weight not reported.

Given that the powder was not known I ran QuickLOAD simulations on AR2209 and Re-17

The peak pressure to result in that particular velocity with those powders within the CoL range is then predicted to be somewhere in the range of 71.7 - 72.7 kPSI

A lighter bullet (100gr) and faster powder (BM2);
69.5kPSI - 71.9kPSI predicted peak pressures for the onset of sticky bolt lift.

130-140gr bullets, loose primers: 75-77,000 PSI peak predicted.

Just wrapping this thread up from my perspective. I did a bit of testing on my own 6.5x47 - Barnard action so not necessarily a good choice for showing pressure signs, but it is what it is. I pushed the peak pressure up to what I estimate was 68kPSI while measuring case head expansion just above the extraction groove. Wasn't willing to go any further. Multiple firings, multiple cases, and less than or equal to 0.0002" expansion averaged. That would give loose pockets on multiple firings but not immediately, not for a while. My reticence to stuff the cases any further and get beyond 70kPSI and/or a thou of expansion per firing will be understood when I say that this was already a 44gr compressed load giving 3000 ft/sec with 140gr VLDs from a 30" barrel from a slow batch of 2209. Plus I couldn't find any accuracy up above 2900 ft/sec so no real point in staying up there.