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Burn Rate?

Brian in Montana

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I know that to find a good bullet/powder combination pretty much comes down to what the gun "likes". However, there's got to be a little more science to it than that. When it comes to burn rates, all else being equal, can it be expected that a slower burning powder would be more likely to produce accuracy when pushing a heavier or lighter bullet for the caliber of rifle your working with?

All I really understand about burn rates is the slower the burn the longer it takes the bullet to travel down the barrel. So that does things to pressures obviously, but will it have a predictable effect on accuracy in relation to bullet weight?
 
In my experience, when using a heavy for caliber bullet, the slower burn powders give better accuracy and many times,also faster velocity in most situations.
Slower burn rate powders will usually require a lower weight charge than a faster powder does to achieve the same velocities, too.
But the slower powder may not do so well with light for caliber bullets.
Barrel twist rate and chamber throat depth makes it different in different rifles.
The trick is to get all the powder to burn up completely, before the bullet leaves the barrel, and thus getting the most push as possible, and at the same time, finding the least amount of barrel harmonic vibration (or at least the most consistent) to give good bullet flight for best accuracy.
The experimentation is half the fun.
Next to shooting of course.

Hope you have plenty of both. Good luck and happy loading.
 
I did some digging around about this question on the internets tonight. Among various nuggets of wisdom I found this; I thought it made a lot of sense:

"Well basically, in an extreme, that combination is much like a grenade. In smaller errors, such as H110 behind an 80 SMK, or RL-15 behind a 30 grainer, you just get crappy performance, and sacrifice the best aspects of both the bullet and the powder.

To elaborate and elucidate: fast powders are much more energetic immediately following ignition, and need relatively little pressure in front of them to generate complete combustion. They have generated peak pressure and are falling off by the time a slower powder has really gotten going. Thus, if you put a heavy blockage (bullet) in front of powder that is extremely fast...the pressure spike has no place to go, overcomes either the brass, the barrel, or both...and you can have a real problem. At best, you give up velocity and accuracy.

Contrast a slow powder which needs a much more inertia in front of it to generate correct pressure for complete combustion. Slow powders reach peak pressure later, but maintain the pressure for longer. This allows them to push heavy bullets to higher velocities than a fast powder. Putting them behind a light bullet causes them to not combust properly, and you lose a ton of velocity, regardless of barrel length. All that unburnt or partially burnt powder does nothing good for accurate fire, as upon exiting the muzzle, those grains WILL ignite in the open air....right behind the base of your now-yawing bullet.

There are a few powders out there that can accomplish a wide range of tasks, but always choose the right powder for the job.

-Nate"
 
For heavy for caliber bullets( 105+gr in 243 Win for example) a slow burn rate powder will give you more velocity.
So it will actually push the bullet through the barrel faster, not slower.
Also you will use MORE powder weight than a fast burning powder.
For example H414 is slower burning than Varget.
In a 7mm-08 you would use about 47gr of H414 or 42gr of Varget.
 

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