Varget and W-748 are about the same burn rate, so does that mean that 20 grains of each burn in about the same length of time and therefore produce about the same pressure? If the manual says 30 gr of Varget can you substitute 30 grains of W-748? I've always followed the manuals to the letter but have always wondered about substituting. Is there a legitimate safety reason for not doing it?
Burn Rates and Powder Substitution
- Thread starter bsekf
- Start date
The short answer is no or maybe yes, sometimes! First off 748 is a double based powder meaning that it derives it energy from both nitrocellulose and nitroglycerin while Varget relies on only nitrocellulose for its energy. They also burn differently one being digressive and one being progressive. The charge weight for the same energy may/will/maybe be different. Same burn rate tends to imply that the powders will produce similar velocity and peak pressure in the same cartridge. Unfortunately it is cartridge specific and there is not specific test procedure to test for the data shown on the various burn rate charts.
Norma has a good page that shows rankings of powder when shot in 308 (Linked below) with velocity and pressure data.
www.norma-ammunition.com
Norma has a good page that shows rankings of powder when shot in 308 (Linked below) with velocity and pressure data.
Reloading Data | Data for handloading with every caliber
NORMA wants to contribute to development and therefor we share approved reloading data for handloading with every caliber. Learn more about hand loading here!
www.norma-ammunition.com
Yes! Burn rate charts are frequently inaccurate, in some cases by a considerable amount. Comparing charts from several sources usually gives different relative positions between pairs of powders. If you base charges on apparent similarities between powders, the 'new' powder may behave similarly to another known grade with a similar rate, but equally often the pair's pressure barrel tested maxima will vary by enough to either produce disappointing pressures and performance; worse, go the other way and produce dangerous pressures.
Even if they were accurate, burn rate is only one of several characteristics that determine maximum loads. Specific energy levels vary considerably, for instance.
These and other reasons are why every such chart available has a 'health warning' to the effect that they must only be used as source of general information, never to determine loads through extrapolation between powders. It's quite legitimate to use burn-rate charts to identify possible replacements for an existing known grade, but then vital to look up their pressure barrel -tested data from legitimate published sources to see if it they are actually suitable, and if so, their charges.
What cartridge are you loading? There should be max load data for both powders in the reloading manuals. I would not go over max unless i had a good feel for the pressure, then only in very small steps!
RegionRat
Gold $$ Contributor
We don't model pressure with only the burn rate, so we should stop that line of thinking in it's tracks and take a moment to understand. To be plain, do not use burn rate charts to substitute for load data.
The burn rate charts are well intentioned, but it may as well have a big warning on the header that they do not represent a load data exchange or predict pressure.
I'm not going to go so far as to say Burn Rate charts are inconsequential, but I will warn the OP not to try and use them as a direct guide in the way one would use a trusted loading manual.
Closed bomb tests that run all the powders through a single standard do not exist to my knowledge, and since those different tests and chambers respond differently to the different powder chemistry types, shapes, densities, and additives, etc., there is no such thing as a universal burn rate chart with equal units.
Even considering burn rate from a specific chemistry type, manufacturing method, shape, density etc., to the very next one, there are serious adjustments made to be able to predict cartridge/gun pressures. When you jump to dissimilar chemistry, manufacturing method, density, shape, etc., the burn rate comparison is even less reliable.
Further... even if there was such a chart, one that ran all the powders through an identical test, it would only apply to that standardized test and the way that test is run. Make any changes in terms of temperature, pressure, volume, ignition method, charge mass, etc., and several entries would change position in a significant way.
Closed bomb testing still goes on all the time. The purpose is for the labs at the factories to have some QC controls, but do not assume for a minute that is the only one that determines the outcome.
If the OP wants to dive a little deeper than a listing of powders on those charts, I would suggest one of the text books on internal ballistics and one or both of the available models, namely GRT and/or QL.
The burn rate charts are well intentioned, but it may as well have a big warning on the header that they do not represent a load data exchange or predict pressure.
I'm not going to go so far as to say Burn Rate charts are inconsequential, but I will warn the OP not to try and use them as a direct guide in the way one would use a trusted loading manual.
Closed bomb tests that run all the powders through a single standard do not exist to my knowledge, and since those different tests and chambers respond differently to the different powder chemistry types, shapes, densities, and additives, etc., there is no such thing as a universal burn rate chart with equal units.
Even considering burn rate from a specific chemistry type, manufacturing method, shape, density etc., to the very next one, there are serious adjustments made to be able to predict cartridge/gun pressures. When you jump to dissimilar chemistry, manufacturing method, density, shape, etc., the burn rate comparison is even less reliable.
Further... even if there was such a chart, one that ran all the powders through an identical test, it would only apply to that standardized test and the way that test is run. Make any changes in terms of temperature, pressure, volume, ignition method, charge mass, etc., and several entries would change position in a significant way.
Closed bomb testing still goes on all the time. The purpose is for the labs at the factories to have some QC controls, but do not assume for a minute that is the only one that determines the outcome.
If the OP wants to dive a little deeper than a listing of powders on those charts, I would suggest one of the text books on internal ballistics and one or both of the available models, namely GRT and/or QL.
jackieschmidt
Gold $$ Contributor
I think in scenarios like the OP describes, common sense and a good chronograph are your best friends.
I'd use IMR 4064 but then I have it. Its only downfall is it doesn't. meter well
I think RegionRat covered it about as well as it can be said. Bottom line is, burn rate charts are barely useful.
I use this example a lot because I hear it a lot. Most charts show n120 as being about the same or even slower than H4198. I can promise you that I have never, ever seen that to be the case using it in small 30's, such as a 30 Major and 30BR. In those applications, N120 it's roughly 2 full grains faster than h4198! That's a lot in a small capacity case that we are loading at or near max pressures with in most cases.
I use this example a lot because I hear it a lot. Most charts show n120 as being about the same or even slower than H4198. I can promise you that I have never, ever seen that to be the case using it in small 30's, such as a 30 Major and 30BR. In those applications, N120 it's roughly 2 full grains faster than h4198! That's a lot in a small capacity case that we are loading at or near max pressures with in most cases.
RegionRat
Gold $$ Contributor
It would be best to make sure beginners don't make the mistake of substituting powders based on stumbling across the burn rate charts on the web and not having the benefit of a mentor or load manual with the warnings that this is not what those charts are for.
One of the early papers I was handed gave a few words on the opening that stuck with me before I ever even saw a burn chart. I had seen load data as a kid, but didn't know what a burn rate chart was till after I was taught how to run caloric tests.
Here are some words from 1977 when there was much effort being spent on trying to convert data from different tests into usable burn rates for interior ballistics models.
When I came on the scene, part of my job as a rookie was to help by modernizing the lab methods and computations. We upgraded the data acquisition systems and improved the computational work.
Many folks contributed to the collaboration that brings us from the "analog era" and into "the digital age". The better we made measurements for these folks, the more we found out that we can't always harness mother nature with math and computers. As much as anything, we learned how much we really didn't know. Now 40 years later...
We are still in the position we were in when I started with respect to jumping from a mass of solid powder to hot gas at pressure, but at least some mysteries were solved and others have some light shed into the dark corners that give us some respect for why those words in the above are still true.
Don't try to use a burn chart by itself to substitute load data or guess at pressure. Play it safe. YMMV
Happy New Year!
One of the early papers I was handed gave a few words on the opening that stuck with me before I ever even saw a burn chart. I had seen load data as a kid, but didn't know what a burn rate chart was till after I was taught how to run caloric tests.
Here are some words from 1977 when there was much effort being spent on trying to convert data from different tests into usable burn rates for interior ballistics models.
When I came on the scene, part of my job as a rookie was to help by modernizing the lab methods and computations. We upgraded the data acquisition systems and improved the computational work.
Many folks contributed to the collaboration that brings us from the "analog era" and into "the digital age". The better we made measurements for these folks, the more we found out that we can't always harness mother nature with math and computers. As much as anything, we learned how much we really didn't know. Now 40 years later...
We are still in the position we were in when I started with respect to jumping from a mass of solid powder to hot gas at pressure, but at least some mysteries were solved and others have some light shed into the dark corners that give us some respect for why those words in the above are still true.
Don't try to use a burn chart by itself to substitute load data or guess at pressure. Play it safe. YMMV
Happy New Year!
Simply stated...Let chemists, be chemists. Let them do what they do and lets do what we do, without straying too far, in regard to this.
FeMan
Gold $$ Contributor
A possible reason may be that it isn't a good choice. Both have been around long enough that if W748 worked well in a 6BR it seems you would find it readily.
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.