Velocity plateaus in load testing: Why?

[Popsbengo]

1 minute ago, MJR said:

Shaggy, thanks.

pops, you won't see repeatability, they are three different calibres. 

I wasn't comparing across graphs. There are two series per graph: Is each series (per calibre) an average of x rounds or are you taking two rounds and comparing them?

[brown dog]

Shuggy,

Are you not conflating the possible plateau effects on the deflagration rate of individual particles of propellant caused by additives affecting different stages of the particle's burn differently, (or even variance of through-burn particle burn rate by differing extrusion shape (piobert's law etc - increasing, steady or decreasing surface area during burn)) with a theory here, which purports that small changes to charge weight cause plateaux?

As you know, we shape pressure/velocity curves with additives and varied extrusion shapes - spaghetti, macaroni, star, multicore etc ,  some combinations will increase rate of pressure generation continuously, some will decrease it continuously etc.  I'm not surehow those burn characteristics are related to small changescharge weight, with all else broadly constant. 

The plateau effect being postulated in Satterlee, relates to  small changes to charge weight and not rates of particle deflagration  - to my mind -given that we're not talking about massive pressure excursions- Satterlee's plateaux are an unrelated idea (?)

[Edit to add afterthought, thinking on this over a mug of tea:   If, as is the norm, shot exit is taking place after all-burnt has occurred, additive or extrusion related changes to particle burn rate must surely be irrelevant (?) and they'll only be seen in projectile performance in terms of mv attainable within a given pressure (?). ]

[Popsbengo]

Having re read the Satterlee article there's a glaring issue:  He says after he's located the so-called flat spot he "fiddles with the COAL.." So he's changing the internal volume and therefore changing the pressure profile and therefore the deflagration profile.  He's also extrapolating from individual shots not taking averages.  Not very scientific at all.

Smoke and mirrors.

[MJR]

Pops, I to have wondered that point but then he's probably only moving the seating depth a nominal 0.040 ". How much difference is this likely to make. Presumably the pressure required to start the projectile moving will be very similar to that needed for the seating depth used in the initial load work up? How long will it take to move the projectile that amount?

[Popsbengo]

1 minute ago, MJR said:

Pops, I to have wondered that point but then he's probably only moving the seating depth a nominal 0.040 ". How much difference is this likely to make. Presumably the pressure required to start the projectile moving will be very similar to that needed for the seating depth used in the initial load work up? How long will it take to move the projectile that amount?

Yes but he's claiming tiny percentile changes.  40thou difference on a 6BR (my assumption) is not an insignificant volume change so I don't think we can discount that from the overall reported effect.

[brown dog]

8 minutes ago, Popsbengo said:

Yes but he's claiming tiny percentile changes.  40thou difference on a 6BR (my assumption) is not an insignificant volume change so I don't think we can discount that from the overall reported effect.

Yes, and any move towards or away from the commencement of rifling will also change shot start pressure.

I'm still of the opinion that charge weight (as opposed to particle burn rate) velocity plateaux are bunkum (banjo?)physics  at normal pressures.  But I'll be interested to read Shuggy's take on my preceding post.

[VarmLR]

I've tried Satterlee and OCW.  Whilst I could achieve repeatable results using OCW, Satterlee was something of a challenge, but I finally got there (in .223 at least).

To be fair to Scott Satterlee, he explains that in order to stand a snowball's chance, you need to be meticulous about brass prep, bullet and charge consistency otherwise it can be a waste of time and money.

Brass should ideally be batched by volume and neck tension uniformed between cases.  Bullets should be batched by mass and base to ogive measurement.  Powder charge ought to be as consistently tight on tolerance as you can get it.

His explanation is that unlike OCW, Satterlee concentrates on optimal bullet velocity (not charge weight, as powders will vary batch to batch) because the results are pressure dependant.  Using different powders, he has achieved the same results with the same bullet provided the results are matched in velocity.  In other words, even using different powders, once a node velocity is found, loading to the middle often results in tiny groups and low ES/SD.

I have done this with 69TMK and 60 Vmax bullets using batched, annealed brass, and after loading have use a lee crimp die to try and uniform neck tension.  For my 60vmax bullets, this resulted in an ES over 5 shots of zero at my first attempt once I'd picked the middle load.  I repeated that test at that velocity (3150fps) many times now and average ES is within single figures.  The 69TMK bullets showed three different velocity plateaus, the attached graphical representation is shown below for 12 different loads.  I have repeated this with very similar results on velocity.

Using OCW I coincidentally got a load which corresponded to load ref 6 (24.6gr RS50), so it agreed with the Satterlee results.

I don't claim to fully understand why powders have these pressure insensitive regions but earlier mention of coatings behaviour may well be something to do with it.

I have not had much luck replicating Satterlee results though in 6.5 CM to date.  I don't know why but it's most likely something I'm not taking enough care on in the brass prep stage.  The Satterlee method spat out a load which I then tried at 600m and it wasn't that good.  SD for that load was quite high, as was ES so my own findings confirm that whilst there's something in the Satterlee method, test groups of the so-called central pressure insensitive load should be shot using statistically reliable 5 or 7 shot groups and repeated to determine ES.  If it's unreliable, then it's back to square one.  That's why I prefer to use OCW and determine the lowest ES node. Once that's found, then in spite of powder batch variations, I know that all I need do is find a load with the new powder batch that matches the velocity of the old batch and I have my node.  That has been a very reliable method and here, I concur with Satterlee as he's had much success replicating the same MVs across various powders for the same bullet.  It takes longer to do but at least results on paper can be corroborated between batches and the velocity is there or thereabouts each time.

 

 

 

 

[brown dog]

" explanation is that unlike OCW, Satterlee concentrates on optimal bullet velocity (not charge weight, as powders will vary batch to batch) because the results are pressure dependant.  Using different powders, he has achieved the same results with the same bullet provided the results are matched in velocity. "

Isn't that the same as saying:

In a particular rifle, with a particular bullet, once I find an accurate load, any load giving the same mv with that bullet in that gun will also be accurate ...and it doesn't get affected by which powder I use.

(?)

(So he's simply describing matching barrel-time)

(?)

[Laurie]

7 hours ago, baldie said:

Because Quickload is just a computer programme, that people rely upon far too much.

Real world shooting, shows it up for what it is...a very basic guide.

 

Absolutely! A verfy useful modelling tool to compare options and tool to get starting points for load development, but that's as far as it goes. ........ and there are 'issues' with some propellant default values. Actual load developoment and a good chronograph on the range then tells you what works at what charge and MV levels.

So far as the issue of plateauing goes, there are two issues as already pointed out in previous posts. One is that charge weight / pressure / MV is not a straight-line curve. Many but not all powders peak in MV terms at a given charge weight and produce minimal MV increases after that. You can find references to this back in early postwar days when handloading really got going and authorities like Jack O' Connor, Warren Page, P O Ackley, George C Nonte Jnr and others mention it. All agreed you are already at a too high a charge level when this happens and charges should be backed off not increased. Excessive pressure signs such as hard bolt lift may occur at this point too. This occurrence seems most common with plain single-based extruded types such as traditional IMR grades.

Thne other is the issue of rising charge weights which tend again not to be linear. If going up in 0.5gn steps and a full grain increases MV by 60 fps across batches covering say 3gn, a half grain should see a 30 fps increase, it's common - I'd go further and say normal - to get results like 30, 15, 45, 25, 30 and so on. Where there is a large average change, it's often associated with an equally large change  in ES/SD and this distorts the average on what are small samples. (ES values in a series might see values like 10, 35, 15, 8, 17, 25 lacking consistency although many combinations tend to see larger ES values with low-pressure loads and produce a decreasing trend as charges and pressures rise and the powder gets into its most efficient pressure bracket. The top end load that produces hardly any additional velocity often sees an abrupt move to a very large ES, but again no guarantee.) Rerun the series and as said in an earlier post 9 times out of 10 you get a different detailed result although the trend and the overall average change repeats.

In terms of charge weight accuracy, my early test load batches are all check-weighed on a lab quality electronic scale and I work with plus or minus 0.04gn variations. When I get to fine-tuning, I'll go to the accuracy of the scale limit of 0.02gn. This is accurate enough to see MV changes in series that are loaded in 0.1gn steps which I occasionaly use although I much prefer cartridges and load combinations that aren't finicky and perform well across a fair size charge weight band - not always an option though!

I take Browndog's point about variable (separate) charge artillery and mortar ammunition and the direct charge weight to MV correlation. Sadly, results here aren't entirely applicable to rifle calibre ammunition. As a development engineer who'd been involved in this field once told me, artillery piece and ammunition design is full of predictable results and the vast computing power now available to designers means they do more development in an office than on the range. To use the jargon cause and effect are mostly 'linear' - change factor A by B% and and you get result C multiplied by a constant. As he put it though, smallarms weapons and ammunition are absolutely bedevilled by an interracting mix of linear and non-linear effects that makes prediction very difficult and on-range and pressure barrel validation essential.

[Brillo]

I can understand the theory and reasoning behind the Saterrlee method as I use a combination of OCW and flat spot MV ladders when I load develop for a new barrel/bullet/powder. 

I thought this thread was going somewhere until I read the part about Satterlee saying you could use several different powders, and as long as they all had the same MV the accuracy node would be the same.

This is simply incorrect. From personal experience and discussions with other experienced shooters, you can get a perfect group with a certain powder with given MV but it will probably fail with a different powder with the same MV, even with a powder with the same burn rate. 

Some bullets are very easy to load develop, such as the 155.5 Bergers, but tge Satterlee theory about multiplicity of powder accuracy nodes does not hold true fir something like a long 200 grain bullet (but that’s another story).

[brown dog]

This has to be one of the most technically thought-provoking threads on here for a long while. 

😊Good stuff

[Bob57]

44 minutes ago, MJR said:

Pops, I to have wondered that point but then he's probably only moving the seating depth a nominal 0.040 ". How much difference is this likely to make. Presumably the pressure required to start the projectile moving will be very similar to that needed for the seating depth used in the initial load work up? How long will it take to move the projectile that amount?

I've just been looking at some figures from shooting my 17rem in 2005, all the same powder load and bullets, just different seating depths.

Tight ogv 1.967.

1.967 ogv = 4300 fps av

1.957 ogv = 4322 fps av

1.947 ogv = 4282 fps

Only a small drop on ogv made a fair bit of difference in this little calibre, shows a bit more speed with 10 thou jump than tight on lands, would have been interesting to have kept going down in length.

 

 

[Shuggy]

1 hour ago, Popsbengo said:

Hi Shuggy,  you seem to have a handle on this effect.  Do you actually think the tests done in the original Satterlee article is demonstrating this phenomena amongst the statistical noise?

Not sure which article you mean; the one on 6.5 guys? I reckon that it’s hard to say, as they don’t exactly use a statistically significant sample size. But my point is that the hypothesis of looking for ‘velocity flat spots’ can be explained by well recognised propellant burning rate behaviours.

[Shuggy]

@brown dog No, I don’t think that I’m conflating things. The relationship which can show plateaus/mesas is burning rate vs pressure. Lots of things can change pressure though; charge weight, propellant morphology, temperature, volume, shot start. It’s a complicated subject!

[Popsbengo]

10 minutes ago, Shuggy said:

Not sure which article you mean; the one on 6.5 guys? I reckon that it’s hard to say, as they don’t exactly use a statistically significant sample size. But my point is that the hypothesis of looking for ‘velocity flat spots’ can be explained by well recognised propellant burning rate behaviours.

Yep, the 6.5 Guys link in the OP

I think this whole field is bedevilled with statistical errors and too much credence given to very small sample sizes using measuring equipment with errors not accounted for.

[brown dog]

30 minutes ago, Shuggy said:

@brown dog No, I don’t think that I’m conflating things. The relationship which can show plateaus/mesas is burning rate vs pressure. Lots of things can change pressure though; charge weight, propellant morphology, temperature, volume, shot start. It’s a complicated subject!

I'm really struggling with the idea that, working at safe pressures, fractions of a grain changes to charge weight cause significant enough changes to pressure that the propellant has an empirically observable change to the characteristics of its burn rate - but you're saying that's indeed the case?

[Shuggy]

11 minutes ago, brown dog said:

I'm really struggling with the idea that, working at safe pressures, fractions of a grain changes to charge weight cause significant enough changes to pressure that the propellant has an empirically observable change to the characteristics of its burn rate - but you're saying that's indeed the case?

It certainly can, but not in every case. There is lots of research going into the use of additives to specifically tune these characteristics. As Laurie says, these sorts of things are enough to give a munitions designer a headache. Trying to explain these things theoretically is very difficult and there is little substitute for lots of empirical testing.

[Laurie]

38 minutes ago, Bob57 said:

I've just been looking at some figures from shooting my 17rem in 2005, all the same powder load and bullets, just different seating depths.

Tight ogv 1.967.

1.967 ogv = 4300 fps av

1.957 ogv = 4322 fps av

1.947 ogv = 4282 fps

Only a small drop on ogv made a fair bit of difference in this little calibre, shows a bit more speed with 10 thou jump than tight on lands, would have been interesting to have kept going down in length.

 

 

 

Seating the bullet deeper in rifle cartridges usually has this effect. Intial reductions in COAL may make no change or even a small increase, then a significant MV reduction occurs at a certain point. This used to be mentioned in many loading manuals at one time but has now disappeared. Somewhere I have a manual which memory says is Viht's original edition or an early Lapua one (they only ever did two) where there were results of a test series on a 308 Win cartridge loaded with a lapua manufactured standard 7.62 Nato bullet to roughly 7.62 standard pressures and 2,800 fps MV where the bullets were seated deeper in 10 or 15 thou' steps. When the jump became significant the MV dropped noticeably and stayed at the new level through further COAL reductions. This was quoted as a result of larger jump into the lands gives the bullet 'a run at them' and as it's travelling faster on reaching them gets less of a check and resumes accerating down the barrel quicker than with a short jump.

I saw this effect recently in a 284 with Sierra's new 183gn 'Uber-VLD'. Seating it 'in' as one does with VLDs didn't work - vertical stringing even at 100, so I went to steadily increasing jumps, six of them from just out to 40 thou'. The first five COAL reductions saw no change in MV (but an effect on ES), then at 40 'out', MVs dropped and ES reduced.

This is the opposite of what most people now believe for two or three reasons. First, in small capacity pistol cartridges such as 9mm emp[oying very fast burning powders with near 100% fill-ratios, COAL reduction does increase pressures, potentially dangerously so loading manuals warn against reduced COALs as general advice; second, some powder types if already compressed, particualrly small grain ball powders can see funny / undesirable ignition/burn effects; three QuickLOAD which has a simple equation here that says reduced COAL = reduced initial combustion chamber volume = higher pressure. What many QL users don't understand is that this is based on the assumption that the COAL used sees the bullet ogive close to the lands and there isn't a COAL - chamber mismatch. In the days when many of us started prone shooting with clapped out first gen 7.62 TR rifles whose barrels had seen many thousands of rounds through them and had massively eroded (but fortunately smooth) throats in the chrome-moly barrels these rifles came with, we soon realised that maximum manual charges were meaningless and MVs were substandard because of the large jumps involved. I bought a Mauser '98 action Schultz & Larsen sometime around 1990 from a guy who'd bought it new in 1968 and had used it regularly since in club and regional competition for 22 seasons on its original barrel. I ended up using the old Lapua 185gn D46 FMJBT seated out with hardly any shank in the neck (still nowhere near the lands) and as much Hodgdon B-LC(2) as I could get in the case which was something like 5gn above book max. It was still a modest pressure load.

[Popsbengo]

21 minutes ago, Shuggy said:

It certainly can, but not in every case. There is lots of research going into the use of additives to specifically tune these characteristics. As Laurie says, these sorts of things are enough to give a munitions designer a headache. Trying to explain these things theoretically is very difficult and there is little substitute for lots of empirical testing.

Empirical testing by persons fully conversant with scientific method 🤔

There's some really interesting stuff in this thread.

[Shuggy]

53 minutes ago, Popsbengo said:

Empirical testing by persons fully conversant with scientific method 🤔

There's some really interesting stuff in this thread.

Don’t worry; Bradders will be along in a minute to tell us to just get out and shoot! 🙂

[Bob57]

1 hour ago, Laurie said:

 

Seating the bullet deeper in rifle cartridges usually has this effect. Intial reductions in COAL may make no change or even a small increase, then a significant MV reduction occurs at a certain point. This used to be mentioned in many loading manuals at one time but has now disappeared. Somewhere I have a manual which memory says is Viht's original edition or an early Lapua one (they only ever did two) where there were results of a test series on a 308 Win cartridge loaded with a lapua manufactured standard 7.62 Nato bullet to roughly 7.62 standard pressures and 2,800 fps MV where the bullets were seated deeper in 10 or 15 thou' steps. When the jump became significant the MV dropped noticeably and stayed at the new level through further COAL reductions. This was quoted as a result of larger jump into the lands gives the bullet 'a run at them' and as it's travelling faster on reaching them gets less of a check and resumes accerating down the barrel quicker than with a short jump.

I saw this effect recently in a 284 with Sierra's new 183gn 'Uber-VLD'. Seating it 'in' as one does with VLDs didn't work - vertical stringing even at 100, so I went to steadily increasing jumps, six of them from just out to 40 thou'. The first five COAL reductions saw no change in MV (but an effect on ES), then at 40 'out', MVs dropped and ES reduced.

This is the opposite of what most people now believe for two or three reasons. First, in small capacity pistol cartridges such as 9mm emp[oying very fast burning powders with near 100% fill-ratios, COAL reduction does increase pressures, potentially dangerously so loading manuals warn against reduced COALs as general advice; second, some powder types if already compressed, particualrly small grain ball powders can see funny / undesirable ignition/burn effects; three QuickLOAD which has a simple equation here that says reduced COAL = reduced initial combustion chamber volume = higher pressure. What many QL users don't understand is that this is based on the assumption that the COAL used sees the bullet ogive close to the lands and there isn't a COAL - chamber mismatch. In the days when many of us started prone shooting with clapped out first gen 7.62 TR rifles whose barrels had seen many thousands of rounds through them and had massively eroded (but fortunately smooth) throats in the chrome-moly barrels these rifles came with, we soon realised that maximum manual charges were meaningless and MVs were substandard because of the large jumps involved. I bought a Mauser '98 action Schultz & Larsen sometime around 1990 from a guy who'd bought it new in 1968 and had used it regularly since in club and regional competition for 22 seasons on its original barrel. I ended up using the old Lapua 185gn D46 FMJBT seated out with hardly any shank in the neck (still nowhere near the lands) and as much Hodgdon B-LC(2) as I could get in the case which was something like 5gn above book max. It was still a modest pressure load.

Thanks for that Laurie, I bet you squinted when you sqeezed the trigger first time on 5 grns over max,or did you work up slowly😁.

I've always seen a drop in velocity when i back bullets off more from the lands, except the 204 ruger which showed an increase of + 54 fps av when backed off another 40thou from the first load which were 25 thou off.

A chrono is one of the best things anyone shooting rifles could own, but can also baffle the crap out of you at times, but also very interesting😃

[VarmLR]

3 hours ago, brown dog said:

" explanation is that unlike OCW, Satterlee concentrates on optimal bullet velocity (not charge weight, as powders will vary batch to batch) because the results are pressure dependant.  Using different powders, he has achieved the same results with the same bullet provided the results are matched in velocity. "

Isn't that the same as saying:

In a particular rifle, with a particular bullet, once I find an accurate load, any load giving the same mv with that bullet in that gun will also be accurate ...and it doesn't get affected by which powder I use.

(?)

(So he's simply describing matching barrel-time)

(?)

I think that he is just describing matching barrel time, except for one thing....isn't it possible to achieve similar MV's with slight variations on barrel time due to differences in pressure curve, and distance from the lands?  I only know that switching powders with my .223 that I've had similar results with the same bullet and different powder so an element of that holds water.  As Mark says though, this may not hold true with all bullets.  Some respond better with reduced jump to the lands as they are less jump tolerant than others.  I have only had success with Satterlee with jump tolerant bullets as I rarely load close to the lands.

I think that the debate is healthy, as it's provoking thought into different areas of internal ballistics that we perhaps rarely discuss in detail.

[Laurie]

18 minutes ago, Bob57 said:

Thanks for that Laurie, I bet you squinted when you sqeezed the trigger first time on 5 grns over max,or did you work up slowly😁.

I've always seen a drop in velocity when i back bullets off more from the lands, except the 204 ruger which showed an increase of + 54 fps av when backed off another 40thou from the first load which were 25 thou off.

A chrono is one of the best things anyone shooting rifles could own, but can also baffle the crap out of you at times, but also very interesting😃

 

I just kept working up until I couldn't get any more powder into the case. 'Normal' loads had all the indications of over-light ball powder charges such as huge muzzle flash and poor obturation. I'll stress the barrel in this rifle was an extreme example - I reckon the bullet was getting on for a half inch out of the case-neck before it hit the lands. Despite all logic, it actually shot pretty well for about 18 months, then half way through a 3-distance comp it just stopped performing literally between two shots - would hardly hold the old NRA target's 'black' at 500 yards. (Not that this is extreme. I saw something online last year in The Firearm Blog or somewhere about two milspec M4 or M16 type rifles, one of which had seen 14,000 rounds through it and the other if memory serves 23,000. The barrels had been sectioned and the higher round one was were pretty well smoothbore for three-quarters of its length.

I agree on chronographs. Good and reasonably affordable ones are one of the big steps forward. Back then none of us had a clue what our ammo was doing. It wasn't all bad - in the absence of any pressure guides other than case / primer condition and case life, you had to be cautious with your loads on the better safe than sorry principle. (Not that this stopped the few stupidos you get in any activity who took the highest recommended maximum load they could find and used it as a starting load.)

[meles meles]

We have some tekkernickel knowledge about large bore rifles and how to tune those for extreme accuracy (i.e. choosing which rivet to hit on a tank a few French miles away) but as has previously been stated in this thread, once one comes down to small bore arms then things get exceedingly non-linear with the slightest fluctuations / changes in apparently almost irrelevant factors showing that they do indeed have an effect and ought to be considered.  As an example, thermal expansion of the barrel and a change in its internal diameter will influence accuracy within a string of shots. How important that is depends upon how good a shooter you are: other errors may mask it but it doesn't go away and can combine with another minor factor to suddenly create a significant effect. Once you start to try and optimise accuracy to the degree some people here desire, then you really are well into the field of statistics: i.e. is what you measured actually what you think you measured and relevant, or something different entirely that you aren't even aware of as being important? No two shots will ever be the same. Two shots in and of themselves are not usually statistically relevant.

In the search for the 'velocity plateau', one would be better firing ten shots at each of many, many charge increments, with an exceptionally accurate chronometer, cleaning the barrel to an identical regimen between each shot. Whilst you are doing that, a team of analytical chemists and metallurgists can be preparing each individual round of ammunition for you using lab quality equipment and producing an error audit. Meanwhile, a team of naturalists can go out and talk nicely to all the flutterbies for miles around and ask them politely not to flap their wings for the duration of the experiment. Let's assume that each round of ammunition is produced with a combined error audit of less than 0.1% in weight, length, concentricity and chemical stability, each shot is fired in a barrel whose surface roughness varies by less than 1 micron, along its entire length, for the whole series of , say, 1,000 shots, the temperature on the range varies by less than 0.1 degree Celsius over the same period, the wind speed changes by less than 0.01 m/s, wind direction shifts by no more than 1 degree. Your results, at each 0.1 grain charge increment, show a velocity variation of 3 fps with a standard deviation of 0.2 fps.  Mathematically, have you actually shown anything or is it just random variation ?

We can do the lab work, but in the real world, we just watch agog as the likes of Baldie and select others on here shoot far tighter groups in 'orrid winds and rain, the sun in their eyes when it deems to show up, and they don't even talk the flutterbies into holding a truce. As Bradders might suggest, Quickload etc are valuable tools that can point you in the right direction, and OCW and other practical techniques can refine things further, but ultimately its the skill of the shooter that counts. Experiment to get you close, then go out and practice. And practice. And practice. You get luckier that way ...  

[MJR]

All true and I think Saterlee explains somewhere that he has previously done testing with more rounds but cut it to two at each charge increment for simple economy. No not statistically the thing to do but lighter on the pocket, quicker and less barrel erosion.