Powder burn rate question

knockturnal

knockturnal

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As a general rule of thumb, the longer the barrel and heavier the bullet the slower the powder should burn? Is that right? Say for instance I have a .300 short mag shooting 170gr bullets with a 22" barrel. I could use a faster powder because my barrel isn't long enough for the slower burning stuff? Is this right?
 
no. Optimal powder is determined by capacity, dimensions, and the bullet weight. No reloading manual stipulates a different powder based on barrel length.
 
Obtunded said:
no. Optimal powder is determined by capacity, dimensions, and the bullet weight. No reloading manual stipulates a different powder based on barrel length.
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X2 - Thank you! For any powder to work correctly, it needs to be operating under conditions in which it will be subject to pressures within its operating range, and barrel length is not one of the factors. Generally, the slower the powder, the higher its low end operating pressure, e.g. Bullseye works well from 10K psi and up, but US869 needs at least 40K psi.

One of the most popular reloading myths is that the longer the barrel, the slower the powder that is optimal (and vice-versa) - not true. All powders are completely consumed within a couple of inches of the chamber, regardless of burn rate. At equal pressures and barrel lengths, more of a slower powder will always produce higher MV's than less of a faster powder. A corollary myth is that the higher the cartridge capacity, the longer the barrel that is "needed".
 
No, you still haven't got it.
This is one of the faults I find with the newer loading manuals. Hundreds of pages of, "You must do this, don't do this, don't ever do this, do it this way, to this measurement,---." But no explanation of why to do things or why not to do things.
Just look at a cartridge. If it has a small bore in relation to the capacity, size, of the case, such as a 243 Winchester, it will need slow powder. If it has a big bore and a straight case, it will need much faster powder. That is why shotguns use very fast powder, large bore, straight case and light, for bore size, projectile.
 
Andy, In my post I started out, "No, you still haven't got it." Then when I posted, there was your posting ahead of mine! Of course, I was not referring to your post, because it wasn't there when I wrote mine! I should sent it as a direct, quote to the OP.
Sorry for how it looks.
 
H4831 said:
Andy, In my post I started out, "No, you still haven't got it." Then when I posted, there was your posting ahead of mine! Of course, I was not referring to your post, because it wasn't there when I wrote mine! I should sent it as a direct, quote to the OP.
Sorry for how it looks.
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So I have to stow away the pitchfork and torch I had ready to use? ;)
 
Just another rule of thumb, while we are at it. An efficient powder for a bottle necked case, will be a powder that fills the case up to the base of the bullet, or nearly so, as the proper pressure is reached.
Some powders, H4831 being good example, work best when the bullet as it is loaded, forces down into the powder, to give it compression.
 
knockturnal said:
Thus the term "compressed load". So what would be a good powder to load in a 7mag?
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The traditional, classic powder was H4831. If you could get Norma 205, or the it's successor, called Norma Magnum Rifle Powder, they would be beter.
I'm sure some 7mm magnum reloaders will come on here with some newer powders that are equally as good.
 
with the 7 rm mag you can always use slow powders, but you can go a bit faster if you are using the lightest bullets..
 
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