One, or two "good" powders?

[gitano]

I wuz up 'til the wee hours of the morning paper-whipping some ballistics using QuickLoad, and made an interesting (at least to me ) observation. Looking at the .308 Win. and the .338 Mauser Ackley Improved , I3031 comes out as the "best" powder in almost ALL bullets. In the .257 Roberts Ackley Improved it was I4350. Of course I need to define "best", so here it is:

QL provides a table of potential powders based the specs of the cartridge and some initial input parameters. Some of the specs are:

SAAMI max pressure;
Cartridge OverAll Length;
case capacity;
specific bullet, and so forth.
Some of the input parameters are:
seating depth;
load density (percent of case filled);
barrel length, and so forth.


The output is a table with columns that show:

the the name of the powder,
the charge,
the load density,
the resulting muzzle velocity (MV),
the max pressure,
the % of the charge that burns before the bullet leaves the muzzle,
barrel 'timing' (bbl harmonics related to departure time of the bullet), and
pressure at the muzzle when the bullet leaves.


Often, there are more than 100 resulting powders that have 'potential' based on the input criteria and cartridge specs. While thorough, it's tedious to sort through those, and many of the powders are either European or Australian powders. Some offer high velocities, but use load densities up to the max I allowed (110%) AND burned as little as 60% of that powder before the bullet left the muzzle. Sorting through what was "good enough" was tough under those circumstances. So... I decided to 'contrive' an objective method for scoring the various suggestions.


First, I'm not interested simply in the powder/charge that gives the highest MV. Neither am I obsessed with "efficiency" (defined below), but each of those components have some value to me. So... I calculate the muzzle energy (ME) for each powder selection in the table. Next, I divide the ME by the charge. This results in what I call "efficiency", (units are ft-lbs per grain). To come up with a 'score', I add the, muzzle velocity and % of the charge burned before the bullet leaves the muzzle, subtract the charge weight, and multiply that result by one one-hundredth of the "efficiency". The resulting value is the "score". I then sort the data by "score" ranking them from highest to lowest, and eliminate those powders (foreign) not available to me. I also eliminate all powders whose MVs were not within 100 f/s of the max MV.

What I found interesting, was that for the .338 MAI, I3031 was the top choice for all bullets selected. In the .308 Win, I3031 was also the top choice or within the top three. Furthermore, I3031 didn't even show up in the list of possibles for the .257 RAI. In that cartridge with one exception, I4350 was always the top choice. In that one exception, it was still only down to third place.

"So what?" you might legitimately ask. Well, the "what" is that with literally hundreds of powders available today, and all the hoohah spewed by "gun writers", it is often difficult to sort the wheat from the chaff. I had no predetermined favorite powder chosen for any of these cartridge/bullet selections. In fact, for the .338 MAI, the powder I used to do the actual real-world load workup, didn't even make the final cut. It wasn't within 100 f/s of the top MV.

So... I'm gonna try some I3031 in the MAI and .308 Win., and some I4350 in the .257 RAI. AND, I'm going to do this little exercise for some more cartridge/bullet combinations.

7x57 (100, 115, 139and 165),
8x57 (125, 150, 175, 185, and 196),
6.5x55 (90, 100, 120, 130, 140 and 160).

Then I'm gonna start looking at the wildcats I've "designed" on the 8x56R case.
.323 (125, 150, 175, 185, and 196),
.330 (150, 175, 205, and 220),
.338 (160, 175, 185, 200, 210, 225),
.358 (180, 200, 225, and 250),
.366 (250, 270, 285, and 300).

It'll be interesting (at least to me), to see if a consistant "good" powder is ID'd for each or any of these cartridges, AND to see if "efficiency" goes up or down as bullet weight increases.

Paul

Oh yeah; in the .338 MAI, "efficiency" goes up with each heavier bullet:

160g-63 ft-lbs/gr,
175g-64,
185g-66,
200g-67, and
210g-67.

As it does in the .308 Win:

110g-59 ft-lbs/gr,
130g-62,
150g-63, and
180g-65.

In the .257 RAI, it goes up and down:

75g-48 ft-lbs/gr,
85g-46,
90g-47,
100g-49, and
115g-51.