.357 Magnum Test with Alliant Power Pro 300-MP (July 11, 2016)

[trumpetman]

This is my first post on Brian's forum. I hope you find it informative and helpful as you navigate your way through the barrage of new powders. I love the old ways best, but I find myself being dragged, almost kicking and screaming into the 21st century of reloading. Here goes.

Anyway, I had a "blast" at the range this morning. I tested two loads through a .357 magnum Rossi '92 lever rifle (20" barrel), and through a 5.5" Ruger New Vaquero cowboy revolver. I used Alliant Power Pro 300-MP powder under a 150 grain hard cast truncated cone, flat nose, flat base bullet (TCFN FB) of an approximately brinell hardness 18. The only reason I bought the 300-MP powder is because I can't get Alliant 2400 around here. I'm glad bought it now. 300-MP in these loadings is really good stuff. They do not leave lead deposits in my barrels, and initial results indicate a very useful and accurate addition to the Alliant family of powders. 300-MP fills the case very well when used as designed -- with heavy, magnum loads. With lighter charges of 300-MP I got velocity spreads of more than 200 fps in some loadings, so I abandoned my attempts to use it for reduced-velocity loads. 300-MP is also the best .410 shotshell powder I know of, producing good patterns, great velocities, and low chamber pressures.

I am posting these results of my latest .357 magnum tests here and now for your benefit, but please realize this data is not in the Alliant reloading guide, nor is it on their web site. I cannot be responsible for your results. The following loads were slowly and carefully worked up from a ridiculously reduced starting load of 13.5 grains of 300-MP (which produced abysmal results). The two loads listed here are both very useable, and the heavier load is extremely consistent. I do not know the chamber pressure of these loads. (This cautions bears repeating.) I do not have any pressure-reading equipment.

LOAD #1

Date: July 11, 2016

Powder: 16.0 grains Alliant Power Pro 300-MP

Brass: New Armscor .357 magnum

Bullet: 150 grain TCFN FB, 18 bnh, Liquid Alox lube added

Primer: Win SP

C.O.L: 1.60"

Very Firm Crimp

Temperature: 68 degrees F.

5.5" barrel: 10-shot average = 1,113.7 fps, standard deviation = 28.2, spread = 91 fps

20" barrel: 10-shot average = 1,686.8 fps, standard deviation = 25.2, spread = 81 fps

Chamber Pressure: UNKNOWN !!!

LOAD #2

Date: July 11, 2016

Powder: 18.5 grains Alliant Power Pro 300-MP

Brass: New Armscor .357 magnum

Bullet: 150 grain TCFN FB, 18 bnh, Liquid Alox lube added

Primer: Win SP

C.O.L" 1.60"

Very Firm Crimp

Temperature: 68 degrees F.

5.5" barrel: 10-shot average = 1,371.5 fps, standard deviation = 16.3, spread = 54 fps

20" barrel: 10-shot average = 1,937.2 fps, standard deviation = 13.5, spread = 41 fps

Chamber Pressure: UNKNOWN !!!

NOTE: The maximum powder drop listed by Alliant for this powder for a 158-grain jacketed Gold Dot bullet is 18.6 grains. Since my hard cast bullet is lighter than the book load, I felt safe to work up to 18.5 grains. In addition, I chose a bullet that produces a C.O.L. (cartridge overall length) of 1.60", which is the SAAMI maximum for .357 magnum. I did that in an effort to lessen the possibility of over-pressuring an experimental load. Please be cautious if you decide to pursue the above loads. In addition to the above loads, I have tested 300-MP with jacketed bullets with very good results. Also, other reloaders have posted some results of 300-MP with jacketed bullets, and they seem to agree with Alliant on at least one thing: 300-MP works best with standard primers. One more thing -- be advised that Alliant's advertised velocity of 1,686 fps for 300-MP with a 158 grain jacketed bullet was achieved with a maximum charge through a 10" barrel, using a Federal 100 (SP standard) primer.

Good luck to all.