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Old July 18, 2012, 09:50 AM   #1
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Powder burn rate: Can someone help explain this to me?

Ok, so from my understanding, different powders burn at different rates, some slow and some faster than others. This affects how the round react (How exactly I'm still trying to grasp), correct me if I'm wrong, but the faster the burn rate, the larget the combustion, and the faster the round goes, which also leads to higher chamber pressures which may damage firearms not designed for a "hot" load?

On the other hand, slower burning powders may yield and underpowered cartridge for some firearms leading to failure to properly cycle or what have you.

An example I can think of is the M1 Garand, it likes a very specific type of powder and deviation from this can cause many problems, such as a bent op rod from loads that are too hot.

Now, in regards to this, how do I know what kind of powder is in commercial ammunition and what would be safe to fire in my rifles? I can read a box all day, but I'm not entirely sure what I'm looking for really.

Some more clarification on this would be appreciated.
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Old July 18, 2012, 09:59 AM   #2
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You can easily prevent what you're talking about by matching the powder speed to the case capacity and the bullet weight.

You do that by consulting a reloading manual.

Commercially reloaded ammunition from the large manufacturers is going to be safe in your firearm unless it is in poor condition or if it is an antique designed for use with black powder.
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Old July 18, 2012, 10:30 AM   #3
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The optimum burn rate depends on the case capacity, bullet weight and shape, and the barrel length. In very simplistic terms, slower powders generally require longer barrels, to give the expanding gases more time to work.

FWIW "burn rate" is actually somewhat of a simplistic misnomer; the powder normally burns more or less instantaneously, the difference is the pressure curve created by the expanding gases. The pressure curve of a "slower" powder peaks later.

A real-world illustration is firing milsurp ammo intended for a full-size rifle or machine gun in a short-barreled carbine; this often results in very pronounced muzzle flash and blast as the gases are prematurely vented to the atmosphere.

As the OP points out, burn rate can be a concern in some semi-automatic rifles, particularly older and less flexible gas-operated designs such as the M1 Garand. However, as Mike points out, the majority of commercial ammo is perfectly safe for most firearms.

One of the major attractions of handloading is the ability to "tune" the load to the gun, particularly if it has a shorter or longer barrel than usual for the caliber.
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Old July 18, 2012, 04:16 PM   #4
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Powder burn rate is nothing more than how fast the powder releases its energy. Its only benefit to the reloader is to help choose a powder for a given caliber. Small cases like the .22 hornet require a fast powder; Medium cases like the .243 require a medium bruing rate; large magnum require a slow burning rate. With some calibers there's an over lap. However, you needn't worry about burning rate if you have a good reloading manual.

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Old July 18, 2012, 09:38 PM   #5
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Now, in regards to this, how do I know what kind of powder is in commercial ammunition and what would be safe to fire in my rifles? I can read a box all day, but I'm not entirely sure what I'm looking for really.

Some more clarification on this would be appreciated.
If you want to buy factory ammo, some MFG's make m1 specific ammo, it will say so on the box.

Commercial ammo uses proprietary powder that you cannot get.
All commercial cartridges have a saami specification (sammi = Sporting Arms and Ammunition Manufacturers institute) So that "any" commercial ammo is safe in "any" gun chamberd for it. Of course the one exception I know of is the M1 garand, which was designed to work with the 30-06 ammo avalable when it was designed, which is less powerfull than what we have avalable today, so todays factory ammo isnt good to use.

If loading your own, just keep velocities down around 2500-2700fps, and you will be fine. Some loading manuals actualy have seperate sections devoted specificaly to the M1 garand.
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Old July 18, 2012, 10:20 PM   #6
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Just a bit of burn rate info in regards to the M1 and also applies to M14 actions to prevent damaging the op rod.

It is generally recommended to load between 147-173gr bullets for the M1/M14 using standard jacketed bullet loads.

A powder in the suitable burn rate range for the action of this type of semi auto gas rifle such as IMR 4895, H4895, AA 2495, BL C2, H335, Win 748, IMR 4064 (and there are others).

A good example would be the Sierra Matchking HPBT .308" 168gr with IMR 4895 powder.
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Old July 20, 2012, 10:48 AM   #7
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Not to high jack but with regards to the M1 Garand what bullet weight and powder combo have people used with success and also what Primer? I've heard the primer one needs to use a specific more hardier primer because of (out of breach) OOB fires. Thanks
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Old July 20, 2012, 11:05 AM   #8
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Something no one has mentioned is the fact that modern powders are "progressive" in nature.
Put simply that means they burn at different rates depending on the pressure the burn is happening in. You can prove this for yourself very simply. lay a few grains weight of powder on a non-flammable surface in a thin line & light one end. It burns amazingly slowly. Why? Because there is zero pressure other than atmospheric.

So you have to factor working pressure in a case into the burn rate to get acurate information. Burn rates as published charts are at best a generalization because lots of different powders are designed to run at different pressures & so different burn rates also.
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Old July 20, 2012, 06:14 PM   #9
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In general, powder burn rates are matched to the length of the barrel (burn time) and the weight of the bullet (mass). Optimization of burn rate to bullet weight for a given barrel length is what separates good from not so good.
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