I've seen the burn rate chart that lists them in order but haven't seen one that is specific for 300 BLK nor any other caliber. I guess I'm missing something. It's not that I don't like the powders, it's that I don't want to waste powder. I'll probably end up buying a bottle of 1680 from WGS.
Separate question, I tried the 700x in my MN using the load data in the cast bullet manual. It hit paper but wasn't accurate. I think it might be because I need to use a filler. Where do I get kapok or could I use TP or polyfill. I've seen a video where the polyfill started to gum up the barrel but thought I'd ask since I have a bag of it in the garage.
Also, does anyone have an answer to my x39 question? Mahalo.
There is no powder that is specific for 300 BLK or any other caliber. This is why you reload and test. However, there is a range of burn speed that is specific to the platform/cartridge/bullet you are using. For instance, generally speaking in rifle powders you would use faster burning powders for lighter bullets and slower burning powders for heavier bullets. Then there are the magnum cartridges which use an even slower burning powder. I would say generally speaking IMR4198 is probably the cut off between slower rifle powders and faster burning pistol powders. The same general rule of thumb also applies to pistol powders. The slower pistol powders are used for magnum cartridges for a magnum load. If you use a faster burning powder you won't push the bullet up to magnum speeds. And then you get into the shotgun powders which are the fastest burning of the powders. The line is too blurred between pistol and shotgun powders so I won't even try to say where that line is.
With that said Hodgdon just started marketing a powder specifically for 300 BLK. Of course it is in the same burn rate as the powders we listed above. Technically speaking it is not specifically designed for 300 BLK as it can also be used in magnum pistol cartridges as well. It is just a marketing tool. I will bet they sell a ton of it at a higher price than the bottle of whatever powder with almost the exact same burn rate.
Then there are powder uses outside the general norm. Like the 300 BLK. Because the developers of this carriage were trying to recreate the velocities of the 7.62x39 cartridge they had to use a little faster burning powder than the traditional rifle powder. Which is why magnum pistol powders are used. Which is also why you don't want to use a powder too far outside the general burn speeds that the cartridge/bullet/platform was designed for.
To continue with uses outside the norm you found by reading the Internet that shooting a single shot/bolt action rifle opens up a world of different choices for reduced loads. People found that a very small amount of fast burning pistol/shotgun powder in a big rifle cartridge gives you a slow moving bullet capable of ringing a gong or grouping decently at 50-100 yards. But this same misuse of powder does not work with a semi auto which is designed to be used with a cartridge that develops a specific range of pressure. Let me just say that the misuse of powder in any application has risks.
In order to ring out maximum accuracy out of any rifle you need to use the correct bullet for your particular rifle (not the bullet designed for your rifle). Like with a MN having such a variety of different bore diameters that you need to find out what your bore diameter is and use the correct bullet for your specific rifle in order to get the accuracy these rifle are capable of. This also means using the right powder for the bullet that works. That is why I always suggest using only published powders in the amounts listed. I found the listed most accurate loads are sometimes absolutely correct in my guns. That is why they list them. Using loads from anonymous people from the Internet has risks as well. I would suggest you stick to published data until you find the best bullet/load for your gun and then experiment with using the incorrect powder for light loads and economy.