I have been loading for about 22 yrs. I have loaded the 7-08 for about 11 years. question? why can i load 44 grs of RL-15 and get 2944 fps. "shot over chrony" and load another powder say, 4064 or varget to the SOME volcity, 2944 or real close, and not get the same accurace. RL-15 will shoot most time .750 at 100 meters.with 140 sierra B.T.

harmonic vibration of the barrel, and the timing of those harmonics when the bullet clears the muzzle.

[QUOTE]Originally posted by Tailgunner:
harmonic vibration of the barrel, and the timing of those harmonics when the bullet clears the muzzle.[/QUOTE

Yup. Also I recently read on a web site that states that the slower burning powders gasses can slightly disrupts the flight of the bullet. It supposedly does this the moment the bullet leaves the barrel and the larger amount of gasses from the slower powder causing a turbulence at the moment the bullet leaves. I will find the web site again and post it here. I dont totally beleive it but I am sure there is some merit to that theory.

I've heard this too and I believe it affects boat tail bullets more than flat base, if it is true.

However, if it is the case then why do so many shooters claim excellent accuracy, for example, in a 270 with Re22 powder (slow), and H1000? And now using pwdrs such as Retumbo and Re25 in a 7RemMag...these are slow powders but sure seem to create great accuracy.

The difference is in the operating pressures of those cartridges with those slow powders. If slow-for-catridge powders are fired at low pressures, they don't combust completely. Partial combustion leaves "imperfect gases", which are less consistent than "perfect gases".

WRT the original post -- you CAN get that same accuracy with the other powders, but you have to make the BARREL TIME equal, rather than the BULLET SPEED. The barrel harmonics is, as mentioned, what counts.

We are playing with some of these things now, using Quickload to estimate barrel time, and damned if we aren't zeroing in on the "sweet spots" of different powders within half a grain to a grain. FWIW, Dutch.

Harmonics are worth considering as well as the uniformity of burn creating the pressure. All powders have a pressure point where burn uniformity is best achieved and it sounds like you found it with RL 15. Problem is, we all want to find it where we get high enough velocity to go along with it for hunting loads. I may be on my own here, but one thing I have noticed in hangun cartridges is that the denser a powder is in some cases, not all, the easier it is to achieve both accuracy and velocity, measurable by standard deviation.

Since you mentioned 7mm-08, I'll tell you that there is a project I am considering with it and buying a rifle for it. Ramshot is importing a powder called Hunter that is in an appropriate burn rate for high velocity potential 7mm-08 loads, as well as .260 Rem, 6.5 X.284 and others like the .280, .270, .30-06 depending on your burn rate speed preference. This is a very dense ball powder (950 grams per liter, or .950/cc) without the temperature sensitivity issues commonly associated with ball type rifle powders. It is said to rival extruded powders in fact. Energy potential for high velocity loading is very good and of course metering would be a non-issue. The listed Standard Deviations for published loads are outstanding. If this holds, it could become one very popular powder for this class of cartridge where you might be currently using several powders ranging from Reloader 15 up to IMR-4831 to find the right performace for a particular load.

Out come the experts with theory...I have a better idea! shit happens!

It is about harmonics, it's also about how uniform the powder is. Your exp. w/ your 7-08 is sim. to what I have had w/ several diff. calibers. You are using powders w/ very sim. burn rates (BTW Dutch, they would be classified as med. burners, not slow) that's why your vel. are close. However they do burn in slightly diff. ways, this cause the bbl. to vibrate diff. My .338-06 drives me nuts w/ this, grouping RL15 loads very uniformly but throwing bullets all over the place w/ Varget, 4064 & vv150. That's why we handload, to get the best perf. from our individual rifles.
Of course, Ray's response has good merit.

I don't think of powder vs. powder the way you do. I tend to think along the lines of brand vs. brand. I'm still mad at W-W for discontinuing W-785! Well, they did it again with WMR...
Let's see what Hodgdon does with the IMR series.

KLN 357
Have you consiered Varget for the 260/, 7/08 (even 280) applications? It does all you claim Hunter does in my same guns.

Did you consider trying to vary bullet seating depth? If it is harmonics you might can "time" when the bullet leaves the barrel at the right harmonic by varying seating depth. Top accuracy isnt always with the bullet seated just off the lands.

Just a thought. Lets see what it stirs up.

I am always amazed by the guys that log so many posts and get offended when someone gets into technical aspects to the point they are annoyed. How many times can one person respond with "Shit Happens"?

I do understand if Math and physics are a struggle for some. I'm not much of a technogeek, but I work in design and pressure is an everyday consideration in what I do. So, get over it.

Cossack, Varget is a great powder and worth having. For me it is a little fast, except for lighter bullets and load density can be better with a slower burner. Velocity too, in the heavier half of the bullet weight range. If we don't look at the possibilities, the possibilities pass us by!

Hello the campfire:
The question was as I remember it, Why do two differant powders loaded to give the same velocity give differant degrees of accuracy?
Harmonics is one factor, as is rate of burn and the particular firearm that it is fired in. Know we know that distance form the lands has an effect, the tightness of the throut, the depth of the rifleing and rifleing type. This is why some rifles like a particular load and other just like it don't.
What would the fun be if every load shot the same as every other load?
A firearm is a system, and the parts of the system must be in balance to achive acceptable results. The more fine tuning you give the system the better you feel about it. Like a souped up car, it all depende on what you are willing to expend to make it what you want. The more highly tuned a system is, the more likely that a small change will derail the whole shooting match. It is a mater of tolerances. Systems with loose tolerances will absorb larger changes than a tight system. which is the reason that standard issue and hunting rifles will handle almost anything you want to feed them, while a beanch rest rifle will hickup if our load is not perfect or the weather is too hot or cold or damp or dry.
Just my ignorant opinion.
Judge Sharpe

This is truly a good study however, the reason it happens is explainable. The shorter (medium) burn rate powders will typically work better with a boat tail bullet while the flat base bullets will take a little longer burning powder. Why do you think that is? Areodynamics!!! Inside the barrel the powder achieves the same pressure, say, 60,000 psi from each but, the key is how long it takes and how far the bullets travel in that time...if the bullet goes to 3.5 inches of the barrel with powder x to get 60,000 psi, then only goes 2.0 inches down the barrel to get 60,000 psi with powder y, powder y gets the pressure with a lower volume of gas where powder x gets it with a larger volume over a more extended length of time...powder x will have excess gas out the barrel and powder y will not have nearly as much. Cut a boat tail bullet down the center and what do you have? An airplane wing pretty much. The gases passing around the bullet as it leaves the barrel usually have little affect due to the length and width of the dissipation of theses gases however, put a lot of slow powder in the mix and whalla, you can see the bullet totally engulfed in the flame(translated...hot gases hitting the air), which acts like turbulence around the wing of an airplane only, the bullet is spinning 20,000 rpm and the gases can only marginally bend the bullet, enough though to change the trajectory as much as 1 moa...more later.

Please don't think ill of me for being so nitpicky, but:

It's not "harmonics". Harmonics are multiples of a frequency, i.e., the 2nd harmonic of 100 Hz is 200 Hz, the 3rd is 300 Hz, etc.

It's "barrel whip", or "barrel vibration", or, if you like, even "barrel harmonic motion".

The barrel does simultaneously vibrate on multiple frequencies... that's true. That's part of the confusion, even though these multiple modes are not technically harmonics.

End of rant. Thank you for your indulgence. I feel better.