[Darkker]

Those are calculations of properties, based upon assumptions of properties, in the quantities of Kg/M³.......

Volume Measured Density is a measurement of fact, not assumptions, and not estimations. Lee publishes VMD's based upon estimations of lot averages provided from the brand names you know. Those people do not manufacture the gunpowder, and they don't get it from the same lot, or age, or source. Which is why I pointed out that you weren't using numbers from your own powder, to make a judgement of consumption.

Cheers

 

[unclenick]

Powder bulk densities (and, therefore, VMDs) are affected by manufacturing tolerances, transport vibration and other factors. Lee's numbers are based on lots they've sampled, as near as I can tell, because of the disagreement between their numbers and those published by Western for Ramshot and Accurate. Western used to publish the bulk density and its tolerance as well as an average VMD number for their powders before Hornady took them over. You can still use the Wayback machine to find them, but I can save you the trouble, as I compiled them in an Excel file long ago (and updated in 2021) and made the following table comparing the Lee and Accurate numbers.

In addition, allow that lot-to-lot burn rate variation is usually about ±3%, and you can see that there is always some lot-specific information. In the case of my previous post, the powder estimates are for your lot as measured in the Precision Reloading test gun. If you are willing to spend the money, sending half a dozen rounds of your original load to the new test facility will give you some idea of how closely his measurements compare for cross-calibration purposes.

Also, note that stick powders can compress a lot more than most spherical powders just because there are a lot of orientations of the stick grains. Below is IMR4064 as poured through different drop tubes for comparison. I should make a set of images of a spherical choice for comparison, but it compresses a lot less. This is a principal reason powder measure vibration doesn't change its density as much as it does for sticks and flakes and flattened sphere shapes you commonly see in canister-grade powder.

 

[JWSmith1959]

I've used Precision labs a time or two and they do jillions of tests for many trap shooters. I trust them. You want to make sure with shotshell loads you want to make sure you aren't grossly over pressure.

Darkker makes a moot point on pressure testing....We have to be able to trust what is published or we're all just spitting in the wind.

 

[Silver_Is_Money]

Those VMD's are very helpful. Thanks!!!

These are my personally measured VMD's derived from MEC bushing drops through 600JR.'s for a few Accurate powders:

Nitro 100 NF = 0.1365
AA#7 = 0.0688
AA#9 = 0.0679

Each of these is of new 2023 manufacture and each carries the Hodgdon brand name on the label. I'm presuming General Dynamics in St. Marks, FL to be the manufacturer.

 

[unclenick]

Darkker makes a moot point on pressure testing....We have to be able to trust what is published or we're all just spitting in the wind.

But it's only a starting point and sometimes has to be taken with a grain of salt. For example, when you see two published data sources, and the max load for one is near the start of the other.

For a more complex example, look at the Western load data for 223/5.56 at 62,366 psi (conversion from the European 4300 Bar). They want to match the MAP used in Europe for both 223 Rem and 5.56 NATO. I looked at their powder charge differences in QL and GRT and found it produces a genuine 12% increase over their 55,000 psi 223 loads. But every source of military data shows the pressure difference between M196 and M855 (our version of SS109) is just a 6% pressure increase (52,000 CUP to 55,000 CUP or 55,000 psi to 58,100 psi). So how did 6% turn into 12%? I called Western not long before they were bought out by Hodgdon and spoke to one of the technicians who'd been in on the tests. He confirmed they were done using a conformal transducer, which does not read the small diameter case as high as the Kistler channel transducers used in Europe do. "Well, that's OK," I said, "but did you calibrate the gun with CIP or NATO reference loads?" "Uh. No. SAAMI reference loads." "Then," I explained, "you are not reading the same 62,366 psi that NATO and the CIP are." Response, "Huh! Yeah, that makes sense." That was the last time I spoke with them. Nothing has changed in the published data, despite the fact you can easily prove it is overpressure by the official ratings.

Of course, this is all still below the proof pressure. The only consequence should be accelerated throat erosion and not serious damage. Still, it's an example of the limitations of even published pressure data that Ken Oehler accurately pointed out is, at best, inexact science. If it were exact, why would they tell you to start load development at a lower charge level than the maximum? Why would people occasionally find published starting loads that were already near the pressure limit for their guns (I have found two of these over time)?

Powder lots vary, guns vary, cases vary, bullets vary, primers vary, and, most importantly, pressure numbers from data sources vary. Somewhere along the way, you need to take all that into account, and starting low and working up while watching for pressure signs in your particular set of components is unavoidable if you want to avoid undue gun stress. Since pressure signs have even more variation from round to round than all the above factors do, one thing you can do is make your own strain gauge measurements in place of the usual brass pressure signs. They may not match the SAAMI-style measurements precisely. Still, they are way more consistent than watching for mushroomed primers, case head expansion, or pressure ring expansion with different brands and lots of components. It is unfortunate that Jim Ristowe is folding up his web business. Someone needs to produce the Pressure Trace or its equivalent. If I weren't well past retirement age, I'd consider doing the same thing.

Regarding powder source, look for the country of origin on the container. When there is none, you can always call Hodgdon to ask.

 

[JWSmith1959]

But it's only a starting point and sometimes has to be taken with a grain of salt. For example, when you see two published data sources, and the max load for one is near the start of the other.

For a more complex example, look at the Western load data for 223/5.56 at 62,366 psi (conversion from the European 4300 Bar). They want to match the MAP used in Europe for both 223 Rem and 5.56 NATO. I looked at their powder charge differences in QL and GRT and found it produces a genuine 12% increase over their 55,000 psi 223 loads. But every source of military data shows the pressure difference between M196 and M855 (our version of SS109) is just a 6% pressure increase (52,000 CUP to 55,000 CUP or 55,000 psi to 58,100 psi). So how did 6% turn into 12%? I called Western not long before they were bought out by Hodgdon and spoke to one of the technicians who'd been in on the tests. He confirmed they were done using a conformal transducer, which does not read the small diameter case as high as the Kistler channel transducers used in Europe do. "Well, that's OK," I said, "but did you calibrate the gun with CIP or NATO reference loads?" "Uh. No. SAAMI reference loads." "Then," I explained, "you are not reading the same 62,366 psi that NATO and the CIP are." Response, "Huh! Yeah, that makes sense." That was the last time I spoke with them. Nothing has changed in the published data, despite the fact you can easily prove it is overpressure by the official ratings.

Of course, this is all still below the proof pressure. The only consequence should be accelerated throat erosion and not serious damage. Still, it's an example of the limitations of even published pressure data that Ken Oehler accurately pointed out is, at best, inexact science. If it were exact, why would they tell you to start load development at a lower charge level than the maximum? Why would people occasionally find published starting loads that were already near the pressure limit for their guns (I have found two of these over time)?

Powder lots vary, guns vary, cases vary, bullets vary, primers vary, and, most importantly, pressure numbers from data sources vary. Somewhere along the way, you need to take all that into account, and starting low and working up while watching for pressure signs in your particular set of components is unavoidable if you want to avoid undue gun stress. Since pressure signs have even more variation from round to round than all the above factors do, one thing you can do is make your own strain gauge measurements in place of the usual brass pressure signs. They may not match the SAAMI-style measurements precisely. Still, they are way more consistent than watching for mushroomed primers, case head expansion, or pressure ring expansion with different brands and lots of components. It is unfortunate that Jim Ristowe is folding up his web business. Someone needs to produce the Pressure Trace or its equivalent. If I weren't well past retirement age, I'd consider doing the same thing.

Regarding powder source, look for the country of origin on the container. When there is none, you can always call Hodgdon to ask.

Shotgun loads are NOT the starting point. They ARE the point. That's why so many trapshooters use PR to do load testing for them. With all of the wad types and primer options (primers do make a difference in shotgun), Most 12 gauge loads are easily within SAAMI specs and not a big problem, but when you get to some 410 and 28 gauge stuff, even common field loads can bump up against top pressures. I am many tmes amazed that some of those trap shooters will continue to use powders that run high pressures, but that is a superstitious group.

A few years ago I had some tests run by PR (Precision Reloading) on some buckshot loads in 12 gauge I was working on. There was not a lot of data with the components I was working with.

I was surprised by some of the pressure differences with them versus #8-1/2 and 9 shot even though the payload weight was nearly identical. I was correct that my loads were safe, but still were a couple of thousand PSI over the lighter shot counterparts. IT opened my eyes a little. I had done a lot of research prior to submitting. them for testing.

Here is a link to a thread from another forum where members submitted their target reloads for testing. Some might find it interesting.

Trapshooters.com Members Reloading Data/Recipes that have been LAB TESTED Official Thread | Trapshooters Forum

 

[unclenick]

Yes, understood. I am just trying to make it clear that between powder burn rate, primer, chamber, and measuring system tolerances, there is still variation in what you actually get. With gun pressures, we are always talking about a range of values and not an absolute number. The SAAMI system, for example, gives the 28 ga. a Maximum Average {peak} Pressure of 12,500 psi for a single 10-round sample. But they also allow that the coefficient of variance will be 7.5%, which means the standard deviation can be up to 0.075×12,500 psi or 937.5 psi. It then also allows for a maximum extreme variation (MEV, the extreme spread of pressure) of 937.5 psi×5.16 or 4,837.5 psi among the ten rounds, which, if all the stars lined up wrong and you had a worst case of 9 of the ten rounds at exactly 12,016 psi, the tenth round could be 16,854 psi, and the load would still meet the standard. Further, the standard allows that a second sample could randomly be up to two standard errors larger, adding another 593 psi to all that, bringing the peak up to 17,447 psi. Then, they allow an additional 3 standard errors of increase as the lot ages after manufacturing, raising the possible peak for qualifying ammunition up to 18,336 psi for one round out of ten at some point in the future, and it still qualifies. So you can see why the maximum proof pressure is 22,000 psi. They are allowing for all that potential variation to occur.

In real testing, the standard deviation is usually smaller than SAAMI allows for, and the odds of your nine lowest pressure measurements all landing exactly on MAP-1/10 MEV are tiny, so those high pressures would be pretty rare ducks. I am just pointing out that is what they allow for. The CIP, on the other hand, just makes an absolute limit of 15% above MAP for new loads, which allows them to use a lower proof load level of 125%. I can't think of an incident in which ammo loaded to SAAMI standards damaged a European-made gun, but it is a theoretical possibility, as their 28 ga. MAP for all but their 3" magnum shell is (about 12,000 psi), and the proof pressure for them is about 15,000 psi.

The closest you can come to discerning what a load is doing in your particular gun is to measure what is being experienced by the steel itself directly. That is what is nice about the Pressure Trace instrument and why I hope someone picks it up to keep the product alive. The strain gauge tells you what is happening to your gun's steel rather than inferring it from pressures obtained in a standard V&P test barrel, which requires all the allowances I just described. I note the SAAMI dynamic choke strain measuring approach uses strain gauges, and this is likely because the crushers and transducers have precision issues when you get down too low in pressure.

That link with all the test result postings is interesting, where the information is complete. Unless more shows when you log in, I notice some contributors never provided enough information to be certain what the load was. But otherwise…

 

[243winxb]

Take note that Accurate No 9 has Tin Dioxide as a coating. This helps the position sensitive problems .
Alliantt 2400 doesnt have or need TD. Makes loades with 2400 more accurate in the 357 Magnum.

US2865729A - Coated smokeless powder - Google Patents

 

[Silver_Is_Money]

Take note that Accurate No 9 has Tin Dioxide as a coating. This helps the position sensitive problems .
Alliantt 2400 doesnt have or need TD. Makes loades with 2400 more accurate in the 357 Magnum.

US2865729A - Coated smokeless powder - Google Patents

Why might the presence of Tin Dioxide make AA#9 inherently less accurate than 2400?

 

[243winxb]

The spherical smokeless powder has a problem. TD is used to help correct it.

"Furthermore, in some cartridges, particularly those made for use in match competition where uniform accuracy, velocity, pressure and other ballistic characteristics are a requisite, it I has been found that cartridges containing such powder charges are frequently unsuitable. This disadvantageous property is most apparent when cartridges are fired in a gun pointed downwardly and the powder is positioned near the bullet and away from the primer. Often be- 1 cause of these disadvantages, it has been impossible to 1 use the same propellant in cartridges of different calibers and in some instances, it has been impossible to use powder from the same lot in cartridges of the same caliber but having different types of projectiles."

From link.

 

[Darkker]

🤔
Tin Dioxide is a catalyst, and IIRC one of the components of the anti-coppering agents.

 

[unclenick]

Yep.

Silver_is_money,

The basic problem stems from how spherical propellants are made to burn progressively.

In principle, a round grain starts burning at the surface and shrinks as it is burned up, shrinking the burning surface as it goes. If you do that with a homogenous powder formulation, you get a slower and slower rate of gas evolution as it burns. That slowing combustion gas evolution rate is called digressive burning. It wouldn't matter if the projectile waited for the powder to burn up before it started moving, but that doesn't happen. As the projectile begins moving down a barrel, it has an increasing volume behind it (expansion) for gases to pressurize.

For maximum velocity without pressure getting too high for the gun, ideally, you would want to reach and maintain a constant pressure despite expansion growing the volume. So what you would need for that is a powder that makes gas faster and faster as the bullet goes down the tube, and that's what progressive burning is. Because the bullet accelerates, expansion becomes too rapid for practical progressive powders to keep the pressure constant all the way down the tube. Also, with real bullets, being at peak pressure and acceleration when they escape the muzzle does damage to the bullet (see photos in F. W. Mann's book, The Bullet's Flight…). So, a compromise is to make powders progressively increase the gas evolution until some practical level of expansion is reached, and then let it fall after that. With high-power rifles, the increasing gas evolution rate starts to drop off after the bullet travel is maybe two inches or so, and less for shotgun and handgun cartridges, but some modest amount of distance, anyway.

Getting a shrinking fuel sphere to increase gas evolution while losing surface area is done by having a deterrent gradient from the surface toward the center of the grain core. In other words, the deterrent is most highly concentrated at the surface, so the burn rate is very slow when the surface area is largest, and then that deterrent concentration declines as the grain burns inward and the surface area shrinks, making the burn rate faster and faster to make up for the loss of surface area.

That works OK if the right diminishing deterrent concentration from surface to core of each grain is achieved. Lot-to-lot burn rate variation is mainly due to variation in the achieved deterrent penetration. But there is a big problem. The high surface deterrent concentration makes the powder harder to ignite. There has been a lot of fiddling with formulations, deterrents, additions, and workarounds to minimize that effect. Tin oxide is one of the additions that helps. In the past, going to hotter primers that make hotter spark showers and raise the start pressure has been one workaround to address the ignition problem. But none of them are perfect. You have to try different primers to see the effect. It also helps to have high loading density so the powder can't fall too far forward from the primer.

 

[Silver_Is_Money]

I've been reflecting upon the issue of AA#9 being Spherical and 2400 being flake, with reference to shape dictated efficiency of burn and coatings/deterrents. And I've been reflecting upon safe shotshell pressures being very low by comparison to magnum pistol pressures. And I've also been reflecting upon the various burn rate charts flip flopping the positions of AA#9 and 2400.

It may be that AA#9 (being spherical) experiences both poor ignition and poor burn progression when used within a low pressure shotshell, and that by comparison 2400 may suffer far less as regards both ignition and burn progression issues at low shotshell type pressures than does AA#9. Thus based upon this (my current line of speculative reasoning) my first guess is now that 2400 may show itself to be noticeably to perhaps even appreciably faster burning when used within the confines of shotshells than for AA#9. And require lower charge weights for similar pressures and velocities accordingly.

Your thoughts on this?

 

[Darkker]

Neither of "those powders", are a single thing. They are blended lots, of different ages, of different sources of gunpowder.
Burning rates WILL NEVER be the same.

Moreover, because of the gunpowder triangle, we know that volume affects burning rates....
And since burning rate charts are often times only calculated anyway....

Pretending gunpowder was magically never changing, to pretend gunpowder was magically able to be linearly scaled, to come up with a theoretical calculation of speed.
Does not then allow someone sitting at home, to magically divine burning attributes, when comparing burning charts across time and source.

Cheers

 

[Silver_Is_Money]

More along the lines of my speculation is that if 24 grains of AA#9 developed a rather low 8,400 PSI, then Alliant 2400 at the same 24 grains may potentially develop noticeably more pressure, such that an initial exploratory charge weight for 2400 (with all else remaining the same) should not exceed 24 grains.

 

[Darkker]

... then Alliant 2400 at the same 24 grains may potentially develop noticeably more pressure, such that an initial exploratory charge weight for 2400 (with all else remaining the same) should not exceed 24 grains.

The "all else remaining the same" is the crux of the matter, because it isn't.

Norma is the only one I'm aware of, that stated their standard. It's a 308 with a 150gr bullet, and a 40-something grain charge of a powder I can't recall without the manual in front of me.
Which means every other powder gets loaded to the same charge and combination; and fired.

Now obviously many powders if they were tested in that combination, is pronounced: "anti-tank mine". So they simply estimate what pressure, could have been created; if they had fired it. Is the expansion ratio the same between a shotgun and the 308? No, and the resulting pressures and burning rates won't be the same either. Back to the powder triangle, and how powder operates. If that reference doesn't mean anything to you, bounce over to Hornady's YouTube channel; or podcast source. They did a feature on how powder works within the last 3 months.

A reloader who looks at a burning rate chart, doesn't know when it was last tested; or if it was a reprint from info passed on by someone else. Doesn't know what the standard cartridge combination was, and doesn't know how they estimated things, nor what lot number or manufacturer sourcing was used.

So that's guessing pressures for a given charge, based off of someone else's series of guessing.
Which is perfectly fine, as long as it's understood what is actually happening. 🙂

Cheers

 

[unclenick]

This is why I posted the information from GRT. It shows a sort of minimum number of things you need to know about a powder to guess at pressures and the like. Relative burn rates on a chart don't cut it in and of themselves.

I can say that in the magnum revolver cartridges, Winchester 296 (aka H110) can't be downloaded very far without risk of it extinguishing, whereas 2400 doesn't have that problem. There are curves in the Vihtavuori print manuals 1 and 2 that show how the pressure curves differ with grain shape, and you may want to look at them, but the point is they differ in ways that show they won't respond the same way to loading either up or down, and that's why the relative burn rate charts don't hold up well when you vary the loads and cartridges very far from what was used to develop the burn rate chart.

Where pressure is concerned, burn rate is just one factor. If you had two flake powders with the same burn rate, but one had 4100 kJ/kg of potential chemical energy and the other had 3800 kJ/kg of potential chemical energy, it would take a larger charge of the latter to reach a given pressure than it would of the former because the latter just won't make as much gas per grain. This is despite their matching burn rates.

Powder is a complicated business. I would recommend buying the 2013 Norma load manual for a good rundown of tables and a description of how a relative burn rate table is developed. If you can find an old copy of the second Vihatavuori manual (1995), it is also an educational read, though, you want to keep in mind that copper crushers were still used for the pressure numbers in the CIP standard at the time, whereas they have since been declared obsolete and replaced with piezoelectric transducers.

 

[Silver_Is_Money]

I've sent a revised version of the 1 Oz. 28 Gauge reload as seen in my post #28 above for pressure and velocity testing, with these three changes:

1) 26.4 grains of AA#9 powder (up from 24 grains)
2) #6.5 size nickel plated lead shot (instead of #6 chilled lead shot)
3) This time Tom Armbrust of Ballistics Research will be doing the testing (instead of Precision Reloading)

Ballistics Research also uses a Piezoelectric Transducer for pressure and an Oehler 35 for velocity measurement.

I got a phone call from Tom Armbrust at Ballistics Research yesterday with a preliminary on my pressure and velocity test results for this load (for which the detailed printout will get mailed out to me today) and here are the average results for the 5 shotshells test fired:

Pressure Average (PSI) = 10,520
Pressure EV (PSI) = 1,000
Velocity average (FPS) = 1,321
Velocity EV (FPS) = 27

EV = Extreme Variation (Low to High)

I think I've nailed it for my 28 Gauge upland bird and small game load.

 

[Silver_Is_Money]

Given this level of consistency for AA#9, I may forego experimentation with 2400. The stack height and crimp were nigh-on perfect for this AA#9 load. I fear that with the much fluffier Alliant 2400 the components stack height within the hull may be too tall, leading to the potential for poor looking crimps, or even to crimps which may begin to spring back open with the passing of time.

But then again, the potential of 2400 to be even more uniform, and even more so when its freezing outside, plus my desire to explore and experiment, may eventually drive me to giving 2400 a trial run or two.

 

[Silver_Is_Money]

Look what showed up in my mailbox this morning: