Powder burn rates

[cdoc42]

Does anyone find the relative powder burn rates useful? They are available on Hodgdon's website.

I realize they are only "relative" to each other and not absolute. That is, for sure, #1 is Norma R1 the fastest and the slowest is #144, VihtaVuori 20N29, but within the list I understand one cannot, with certainty, say that #25 is really faster than #26. I was considering grouping them into a series of 5, just to consider that any powder from 1-5 was probably faster than 6-10.

Any thoughts on this?

The reason I got into this is I was reviewing the Hodgdon data for .25-06 and I noticed that if I used H4895 (burning rate list 87)for a 120gr bullet the pressure listed was 1,100 CUP higher than H1000 (list #135), but the velocity was 208 fps slower. It would seem, then, in this case, you could achieve a higher velocity by using the slower powder (higher list number) with less pressure.

It seems it might be helpful to check the burning rate list when deciding on a powder for a given load, and if 2 are within the same 5-member group, pick the slower one as a start.

What do you think?

[PawPaw]

I find Hodgdon's list helpful when I'm comparing powders, although I don't agree that the slower powder is any better than one that's marginally faster. Powder choice depends on the application and some of the powder companies are doing things with pressure that are really compelling. Velocity generally dictated by the area under the pressure curve and some of the newer powders have less pressure, but maintain that pressure longer. Some of the newer powders aren't yet listed on the Hodgdon chart, like the newer powders from Alliant. I've been experimenting with Power Pro 2000 MR in the .308 and finding some really interesting results, yet that powder isn't listed on the burn rate chart.

Lots of folks love Varget for the .308 (for example) and others love Reloder 15, but you find that they're very close on the Hodgdon chart, at #97 and #99. They're both good powders for that cartridge and I'd bet that the powder between them would also be a good powder, although I personally don't have any experience with it.

The burn rate chart is simply another tool in our tool box.

[wncchester]

"It would seem, then, in this case, you could achieve a higher velocity by using the slower powder (higher list number) with less pressure."

Well, yeah. We can reach any pressure we may want with a fast powder but it will never attain the velocity a powder with the proper burn rate will.

I've long found burn rate charts mildly interesting but just as data. Never for choosing a powder to try; I paid good money for my loading books to tell me what works best with any cartridge/bullet weight combo.

[mehavey]

When you see the different pressure curves over the length of the bullet's travel in the barrel, it becomes clearer.

I tend to like boundary-value problems to show physics lessons.
Case in point is using a very fast Powder (Clays) against a relatively
slow powder (RL-25) in a 300WinMag.

Using the req'd amount of each powder to achieve the same peak 55,000psi
max pressure against a 168 Match King, you get the following pressure curves
down the length of the same 24" barrel.



Now remember that:
(1) If you do more Work on a given mass, the faster it goes.
(2) "Work" = Force x the Distance over which you apply that force.
(3) Total work done is therefore directly related to the AREAS under those pressure curves above.

Now which curve has more Area under it over that 24" bullet travel?
The top (fast powder) curve, or the lower (slow powder) curve?

[FrankenMauser]

You forgot the fundamental rule:
Reloading IS rocket science.

You need to match your burn rate, projectile weight, projectile length, bearing surface, jacket/bullet material, case capacity, case shape, barrel length, bore diameter, groove diameter, and everything else you can think of.....


...Or, just shoot from the hip, until you "stumble" across these correlations, and add them to your "experience" file.

I learned to pay attention to burn rates with my .220 Swift. After it was given to me, I noticed that my father's most accurate loads were all using slower powders. When I decided to experiment with W780 (it had NO data at the time), I started with .220 Swift. Using W780 (similar burn rate to 4831), I achieved fantastic results... With a powder that 90% of reloaders would tell me would "never work" in .220 Swift, I was achieving great velocities, and fantastic accuracy. That's when I started to pay attention...

I can't tell you how I pick my powders now, or exactly why. It's just a barrel length/cartridge capacity/bore diameter/bullet length/bullet weight/burn rate juggling act. When I finally get a "gut feeling" that something is a good match, I try it. Lately, I've had great results with these "gut feeling" loads. (And, for popular cartridges, they often deviate substantially from the "classic" pet loads.)

[Jimro]

The powder burn rate chart is really helpful when you want to go into the realm of "no published data" to reload a particular round.

This isn't to say you should ever substitute data for a known powder with your another, but you should be able to make an educated guess as to where to start. If you look at IMR4895, Varget, and IMR4064, you can see that starting loads are generally in the upper 30s for a 308. So if you are reloading for a 308 with a powder that falls in that range but doesn't have any published data, you can start in the upper 30s and do a safe normal load workup.

The other thing that can be helpful is when you design a wildcat (or adopt one) and you look at case capacity to bore ratios. Just like using Win780 in the 22-250 (was once a wildcat) and it doesn't matter that it is just a 22 caliber round, the case to bore capacity makes it ideal for slower powders.

General rule of thumb, the more case to bore capacity the slower the powder you can use.

Jimro

[Doodlebugger45]

Check this one out
http://www.vihtavuori-lapua.com/pdfs...Rate-Chart.pdf

[Doodlebugger45]

A more modern version with a few more powders. I like this format better than a strict numbering system.
http://www.lapua.com/upload/reloadin...echart2011.pdf

All powder burn rates are kind of limited in use. Part of it, besides lot-to-lot variations, is because a given powder will burn at different rates as the pressure goes up. So assigning just one number to a powder and saying that is "THE rate" is an oversimplification.

Nevertheless, I like the Vihtavuori graphical chart better than a tabular format. With most of the rate charts, for all we know #91 to #98 can be practically equal in burn rate, but it might be that there is a big difference between #98 and #99.

Using this chart might tell you that when Vihtavuori's engineers tested powders (to the best of their abilities), if they thought that N-140 and H380 and AA 2700 and RL-15 and Big Game powders were essentially equal, the chart will show them side by side.

[wncchester]

"Reloading IS rocket science." ???

[wncchester]

"Reloading IS rocket science."

Not really. Actually it's not even close to a science, at it's best reloading is a semi-wildazz guessing game. In an established science of any kind we can predict the end results of a change in parameters with a high degree of accuracy and that's certainly not so with reloading. Reloading is unpredictable, especially so when we approach very high OR very low pressures. That's why each of us must approach our reloading methodically, testing each change in small steps before proceeding to a different level of pressure and we aren't doing it by science, we're just feeling our way along.

(OT - That lack of predictibility is why 'global warming' is a loopy scientific farce, those guys can't predict anything accurately but want us to take their hype seriously. I know something about science so I don't take the hot weather Chicken Littles serious at all. Not only can they not tell us what the average global temp really is, they can't tell us what it should be! )

[mehavey]

Not really. Actually it's not even close to a science,

Au contraire, mon ami. It is precisely rocket science as an offshoot practice at no less a place than my USAF Rocket Lab high atop the hill at Edwards AFB. All the elements are there from the propellant chemistry, element size, surface area, center core burn rates/pressure acceleration, nozzle effects, containment vessel design, strength of materials, ignition effects.....

(Including a few "...where the $#!^!! did THAT come from...?" moments.)

Getting educated to all the interplaying elements & edge effects of QuickLoad is the next best thing to a chemistry set from the 1950s in that regard, as are some of the new pressure measurement toys discussed here about six months ago... and a chronograph can open up your world, save your life, and extend your barrel time.

Oh, and did I mention metallurgy ?

Now I'll admit that many of the "artful" aspects of reloading in general have been cleaned up, de-tuned and carefully presented in paint-by-the-numbers fashion by the good folks at Lyman, Hornady, Speer,(et al) including no few book & magazine authors (and contributors even here on FiringLine) who have spent their lives checking out the edge of the envelop where that demon lives in a very disciplined fashion

...and don't forget the powder companies too. Those same good folks who mix, pour and shape my solid rocket boosters.

No. It truly is Rocket Science.... but only as much as you educate yourself to want to explore... and clutter up your reloading area spending both time and money your wife has much better use for.

(And after all that I still can't pin down all the factors that cause my Swift to run hot/fast, or how my 30-06/Model 70 will pitch 180gr pills out at 2,800 w/o breaking a sweat, or where the pesky nodes are on that Mod70's barrel. -- so let's agree to call it "artful science".)

[Jimro]

The Lapua burn rate chart has H870 as slower than AA8700. Unfortunately they are the same powder and should probably be listed side by side.

Jimro

[Sport45]

The Lapua burn rate chart has H870 as slower than AA8700. Unfortunately they are the same powder and should probably be listed side by side.

Yeah, they show the same with W231/HP38 and W298/H110. Same powder, but different burn rates?

The thing I noticed first though, was they had H4198 stuck in between H110 and Lil' Gun. All of the burn rate charts have to be studied with a little skepticism.

[mehavey]

FWIW, QuickLoad (Helmut Brömel who does his own testing so I've been informed) thinks they are different:

        	       AA8700	H870
Explosion Heat/Potent'l	3460	3810
Specific Heat Ratio	1.237	1.2333
Burn Rate	       0.2713	0.2752
Progressivity	         2.66	3.1
Progressivity Limit	0.54	0.54
Factor B             	2.3014	2.411
Density               	1.57	1.62

Thoughts?

.

[Jimro]

More than likely lot to lot variation. The US870 standards probably don't have to be as tight as what we expect from cannister powders, and cannister powders can have significant variations from lot to lot.

Jimro

[black mamba]

I like the graphic nature of the Lapua chart, but it would need to be much longer to accurately depict powder relationships from column to column. The proportions get distorted in order to keep the chart on a single page.

[mehavey]

Relative Burn Rates are useless without knowing the different Energy Densities of the powders being compared.
And as far as I know, QuickLoad is the only comprehensive source of such information easily available to the general public.

Even then, without having a good chronograph you're still flying blind as to what the end result is.

[cdoc42]

Is it also true that burn rates differ from lot to lot in the same powder? That would explain, if it's correct. that cartridge manufacturers load by pressure, not velocity, so they can be more certain pressures are not exceeded. As handloaders we use velocity as a guide which may produce different results from lot to lot if the pressures change enough.-?

[Jimro]

Yes, powders do change from lot to lot. Hence why some lots experience recalls and some don't. I know a bunch of 308 shooters who switched from Varget to RL15 because RL15 had smaller lot to lot variations and made reloading easier.

Jimro

[mehavey]

As Uncle Nick noted a while back, the gov't (and their commercial manufacturers) load to a targeted velocity within a specified pressure range. Powder lots, mixtures and amounts are adjusted accordingly to achieve that aim, which is why different lots of ammunition may have different powder characteristics and entirely different charge weights.

[WESHOOT2]

First and foremost, I concur with the opinion that handloading is science.

Second, I have at least five burn rate charts from different sources, and none is alike.

Third, QUICKBLOWUPYERGUNLOAD is based on many assumptions, and useful only to the educated cautious reloader.

Lastly, I find burn rate charts useful; that's why I have so many.

[mehavey]

QuickLoad is Advanced reloading -- no issue there -- and I always look to 3-4 add'l source/manuals for new loads to make sure I'm in (someone's) limits -- or know the reason why not.

But don't ever sell it short for information available nowhere else, and true understanding of the effects wherein components, assembly, and the physical chemstry are changing. In fact I would so far to say that even loading manuals can be so far apart these days as to be truly dangerous when careful attention as to the exact components tested are ignored. (9mm and 40S&W are classic cases of recent discussion)

As far as pure burn-rate charts go, I'll note again that they are useless without the energy-densities of the powders involved.

[Brian Pfleuger]

QuickLoad, when used properly, is superior to any load manual. It is tailored to MY gun, MY bullets, MY powder, MY OAL...

No, it is not "trustworthy", by default. Neither are the load manuals, hence "start low and work up".

QuickLoad is MUCH better than any manual. Unlimited powder and bullet combination, barrel length changes, searchable parameters like peak pressure, muzzle pressure, rise time, case fill...

Yeah, no manual comes close. Heck, ALL the manuals together don't come close.

BTW, Mehavey, in that chart above with Clays in the 300winmag, did you have barrel friction turned on? Makes quite a difference to muzzle velocity in those situations...

[mehavey]

...in that chart above with Clays in the 300winmag, did you have barrel friction turned on?

Good question.
As far as I know I do, but I'll check when I get home

[mehavey]

By any chance did you mean fiction proofing ?


If so, I normally have that turned OFF (never run any moly-coated projos anyway)