slow vs fast burning powder??

[kennedy]

what does that mean? I am using H4895 for .308 and AA5 for .40 are these fast or slow? how does it effect accuracy? explain the how this works for accuracy. thanks

 

[Kimber1911_06238]

if your charge weight varies slightly, there will be a greater difference in velocity with fast burning powder.

also, you use less of fast burning powder...there is more empty space in the case and depending on where in the case the powder is, velocity can vary.

 

[Mal H]

You have named two powders that are somewhat unrelated. The first, H4895, is a medium speed rifle powder. The second, AA#5, is a medium speed handgun powder.

In general, the burn rate for rifle powders is much slower than for handgun powders. There are some powders with a burn rate that bridges the two groups - IMR 4227 and 2400 come to mind. A caution: Experimenting with handgun powders in rifle cartridges can lead to rapid disassembly of your rifle.

You try to choose a powder with a burn rate (within the proper category) that will fill the case sufficiently without causing too high, or too low a pressure peak depending on many variables such as caliber, bullet weight in that caliber, velocity desired, etc. As Kimber1911 said, if the burn rate is wrong you might have too little in the case which might cause an uneven burn. It depends a lot on the powder type, composition, and primer.

How a burn rate affects accuracy is kind-of up in the air. There are many variables that affect accuracy, burn rate is one of the minor ones. As I said, if you have sufficient powder in the case and the powder is proper for the case/bullet combo, the other variables are more important.

 

[Sport45]

Here is a burn rate chart that you can look at. The larger the number, the slower the powder. There are many charts available like this one and they generally agree with only a few powders swapping places. Like Mal said, the slower powders are typically used for rifle and the faster ones for handgun and shotgun. Within each category I'd say the slower powders usually match up better with heavier bullets or magnum loads.

 

[wworker]

It seems to me that one would need a faster burning powder based on barrel length.

Short barrels as found in pistols would need the fastest burning powders and longer barrel lengths as found in rifles would need a slower burning powder.

Also in a rifle powder, a short carbine would need a faster rifle powder than a long barreled rifle.

Shooting a slower burning rifle powder in a carbine would not maximize the efficiency of the powder, but it would produce a nice fireball out of the muzzle.

 

[brickeyee]

'Burn rate' refers to the time from ignition to peak pressure.
It is a very slow powder (like .50 BMG stuff) that is not totally consumed within a few inches of bullet travel.
Many pistol powders are consumed before the base of the bullet even clears the case.
Rifle powders might make it an inch or two.