Nosler #4 p249 7-08 data for 140 grain bullets

I am looking at the top three velocity loads listed below.

My questions:

1. Some powders produce best accuracy at a minimum charge weight and low density and some at a maximum charge weight and high density, why?

2. With any one powder, when best accuracy is achieved at or near a maximum charge, is this indicitive of a fast or slow powder?

3. Of the three powders listed, would IMR 4350 be the best choice because it produced high velocity with maximum density at the maximum charge weight; in comparison to IMR 4895 and RL 19 which produced best accuracy at the lowest charge weight?

4. With the load which produces the highest velocity using RL 19, best accuracy is at the lowest charge weight, does this mean the powder is to slow?
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RL 19

49.0 2922 fps 100%
47.0 2807 fps 96%
45.0 2692 fps 92% (Most Accurate)

IMR 4895

41.0 2862 fps 84%
39.0 2737 fps 80%
37.0 2612 fps 76% (Most Accurate)

IMR 4350

46.0 2840 fps 94% (Most Accurate)
44.0 2720 fps 90%
42.0 2600 fps 86%

The most accurate powder tested was H335

40.0 2742 fps 83% (Most Accurate)
38.0 2670 fps 78%
36.0 2452 fps 75%

Oilburner

You need to remember that each barrel is unique and what they show is for reference only....safe and/or accurate in that barrel only. A different powder batch (lot) may be different, same for primers both type and lot, plus the rate of twist of your barrel plus a lot of other things that will affect both velocity and accuracy in "your" barrel. Every barrel seems to have a "sweet" spot with respect to accuracy and it mostly has to do with barrel harmonics or vibration...one of the reasons the benchrest boys like short, fat barrels as the amplitude of these harmonics is much less than thinner and longer barrels.

My rule-of-thumb is to first try the powder that comes closest to filling the case at the max load....this really seems to help consistency in both velocity and accuracy for me (with a "full" case the powder is always in the same position which is important).

I'll try to answer all your question with a simple but detailed answer. powders burn differently and therefore create a pressure curve. This pressure curve either builds slow or fast or linearly. and the way the pressure hits the barrel and creates a vibration and this is more indicative to accuracy. To get the barrel to vibrate at the frequency it likes and also to get the highest same velocity possible.
The difference in accuracy between powders is in my opinion the pressure curve it produces and what the barrel likes. And the accuracy that they get may not apply to your rifle. this is the results they received from the rifles they used.
Here is another thing to think about, Rick Jameson of Shooting times did a study on the affects of faster components to slower components. And he found that the same powder, primers, bullets and cases from different lots but of the same model. they produced widely varying velocities.
Kerry

[This message has been edited by Kerry.S (edited 01-12-2002).]

Re-15 is the only propellant I use,in my 7-08's. I've found nothing better,when weighing the harmony of speed and accuracy.

36.5grs start and 40.5 is approaching the upper end,but my barrels will digest more,as I shoot moly......................

It has been my experience that many times Nosler's most accurate loads and my experiments do not agree.

DB Bill provides a good explanation of variables in load/accuracy. As for "speed" of a powder, generally "faster" powders produce a given velocity at higher pressures while "slower" powders produce that same velocity at lower pressures.

Why then would you use a faster powder? It may set up a more favorable harmonic in the barrel and result in greater accuracy. Faster powder typically uses a lighter charge weight and, accordingly, may be more economical to shoot. IPSC shooters prefer faster powders because they produce a shorter recoil interval, thus allowing faster re-acquisition of the target for a follow-up shot.

There are other factors, but these are a partial list.

[This message has been edited by Genghis (edited 01-14-2002).]