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I have been reloading, for rifle and handgun, for over twenty years. During this time I have pretty much stuck with the loads listed in the manuals, primarily Speer manuals. Also, in trying to keep things simple, I have used only a few different powders, such as Bullseye, Unique, 296, IMR4064, and acouple of others. I rarely load to maximum levels, and ususally can find an accurate load by adjusting the powder charge. Once I do that I am content with the load. In various articles I have read that a certain powder is more "accurate" than another, and that leads to my question. Since the expanding gases propel the bullet from the barrel, why do different powders make a difference? I realize that some burn faster and some slower, some are cleaner, etc. etc., but how does one powder make the bullet travel more accurately than another powder would. I can understand how different bullet styles, with different aerodynamics will effect accuracy, but once the powder has been converted into a gas, how can this effect accuracy? If anyone can explain this, I will have learned something of use. Thank You, DGR
 

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Beartooth Regular
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The primary reason a powder may affect accuracy (assuming that you have selected a powder that gives reasonable velocity, pressure, and consistency in the given cartridge) is that the burning rate of the powder may change the length of time that a bullet is inside a barrel and may affect the barrel's vibration characteristics.
When you fire a rifle, the barrel immediately begins to move. It recoils, it whips (like a rope) and it oscillates in a series of waves and nodes. Ideally, you want the bullet to leave the bore when the muzzle is in the same place each time. This might be at the end of a whip, before the barrel starts to whip back the other way, or it may be at a node. The powder can effect these vibration characteristics and the bullet's relationship to them.
Now, in practical terms, powders that are similar in burning rate usually perform similarly. BUT NOT ALWAYS! Also, every physical characteristic of the rifle and how you hold it bears on the equation too, which is why it is very difficult to say with certainty "this load shoots well in my rifle, it will in yours too."

Hope I haven't bored or confused you. In the end, every rifle is a "shoot-it-and-see" proposition, and if you are satisfied with your results, you're all set! IDShooter
 

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The Troll Whisperer (Moderator)
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IDShooter has pretty well defined the answer for you.

By varying the graphite coatings and shape of the powder it can be made fast, slow or inbetween.

The variance in chambers, bore diameters, rate of twist, barrel thickness, combination of components also enter into the equation. The reloading manuals and the trade rags all use various types of actions, barrels and testing parameters to establish their results. It would be extremely hard for you and I to repeat these conditions.

As you have said, you have a select grouping of components that seem to work well for your individual firearms. If you're happy with the results, that's really all that matters. I've tried the recipies listed by the manuals as "most accurate load" and usually find my particular firearms like some other combination for best accuracy. Generally tho, a couple grains below the max listings are the most accurate for me. I'm loading for hunting conditions, not tack driving accuracy of benchrest shooting, so I sacrifice a little on the accuracy side in favor of impact energy. If I can keep my shots inside of a 6" circle at the furtherst range I anticipate shooting, that's the load I go with. Be advised my longest self imposed range is 350 yds these days. Years ago, I'd try at 400-450 yds.

Due to normal higher hunting tempratures, I tend to go with the temprature insensitive powders, due to the near max loadings.
 

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Great post and two well defined answerer's guy's :) I found that temperature changes really make a difference with the way powders react, during the summer working up loads, I get them tight, but as soon as the weather changes to cold in the fall, I set out and retry these loads, you would be surprised how much things can change when you drop 40 degrees, so I just tweak a little for the climate I will be hunting, I also use powders now that tend not to vary as much with temp changes, Hodgdon seems to work well in temp changes, I did noticed ballpowders seems to have greater sensitivity to temp changes well at least decreases in temp. Aim small hit small. RAMbo.
 

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Beartooth Regular
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There's a little to add here. Primers affect the burning rate and can make a difference. Different powders of the same burning rate may not give the same barrel time, even if they give the same velocity. Ball and tubular powders have different pressure curves. Look at it this way. Let's enlarge a ball powder grain to the size of a basket ball and light it. It has a large surface area burning, but by the time it's burned down to golf ball size there isn't much surface area left. This is why ball powders are heavily coated with burning deterrents, so they get off to a slower start. This leads to the common recommendation for magnum primers to make sure they start burning evenly. The large artillery powder grains with 7 perforations are at the opposite extreme. Their burning area increases as they burn, almost to the end.

All of this affects barrel whip and accuracy, and each gun is different. So just because you get fine accuracy with 4064 dosen't mean the next gun off the line will like it. There's usually a standard load that performs well for each calibre, but my .222 hates the standard load of 20.5 grains of 4198 behind a 50 grain bullet. It loves H322.

Bye
Jack
 

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The Hog Whisperer (Administrator)
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I would guess that there can be some slight differences in the fouling left by different powders, and that could affect accuracy also.
 

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You guys are good, we should write a book.

I would like to throw in the notion of powder bulk density, and the extent to which a given charge weight fills the case. Particularly with slower powders, ignition characteristics vary with load density AND powder position in the case. In general with these powders higher load density gives smaller velocity variations, which influences accuracy.

With most pistol powders load density is not a problem because the powders are fast and very easy to ignite uniformly, regardless of load density and/or case position. H110 is a striking exception as it may FAIL to ignite at reduced load densities.
 
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