MP 475

[sqlbullet]

My supply of WC846 powder is getting low.  In fact, by the time I reload the 223 and 308 brass I have right now I will be out.  And it is currently unobtainium.

American Reloading has a powder MP 475.  It appears on the chart between Reloader 12 and Reloader 15, around IMR-4064.  However, unlike most surplus powder, they don't provide a "use XYZ powder data -10% and work up".  They just provide a 223 recipe for 55 grain (that is a little weak at 2990 fps max, barrel length not specified) and for 308 150 grain (in the game at 2900 fps).  I would be loading 223, 55 grain, 308 168 grain and am comfortable working up the 168 grain load based on the data they offer with my chronograph and micrometer.

Anyone ever used this powder and have any thoughts to share? 

[sqlbullet]

Finally got to the range with some load workups.

I was able to test loads from 22.5 grains up to 25.0 grain listed max in all the barrel lengths I had, as well as calibrating to some XM193 ammo.  Velocities were measured using a LabRadar.  Elevation was about 4250 feet surface elevation and temperature was 69° F.  The 18" barrel was a 223 Wylde chamber, while all others were 5.56X45 NATO chambers.  All values are average for 5 shots.

XM193 Reference load

Barrel    Velocity        StDev    ES
20"        3166 fps      48.06    98 fps

MP-475, 25.0 grains, 2.300 COAL, CCI 400 primer, Once fired Wolf Gold brass, 55 gr FMJ

Barrel    Velocity        StDev    ES
20"        3031 fps      21.13    55 fps
18"        2906 fps      42.54    116 fps
16"        2794 fps      52.56    133 fps
10.5"     2487 fps      47.72    128 fps
7.5"       2175 fps      43.94    106 fps

In addition I fired one series of over-max from the 20" barrel.

MP-475, 25.5 grains, 2.300 COAL, CCI 400 primer, Once fired Wolf Gold brass, 55 gr FMJ

Barrel    Velocity        StDev    ES
20"        3095 fps      54.57    122 fps

I would also comment, that despite using softer CCI 400 primers rather than the CCI #41 Military Small Rifle primers with harder cups, the primers still look fresh with very rounded edges compared to the XM193 primers.   25 grains is perfectly useful load that gave full function in all of my rifles and pistols, and delivers adequate velocity.  It is interesting to note that at 23.8 grains extreme spread was very high (215 fps, probably incomplete combustion due to lower pressure), it settled in at around 55-60 for 24.4 grains and 25 grains, then jumped back up for the 25.5 grain load.

I also tested some work-ups in 308 Winchester using 168 grain Sierra MatchKing HPBT bullets in once fired 7.62X51 NATO SBS headstamp brass.  Rifle was a PA-10 with a 20" barrel and a 308 Win chamber. Again, values were for a 5 shot average.  The source data was for 150 grain, and I was shooting 168 grain, I cross correlated the data points with known values for IMR powder, and then used reference data from IMR 4320, reduced and working up.

MP-475, 308 Win, 168 Gr Sierra MatchKing BTHP, Once-fired 7.62 NATO SBS brass, Win LR primer, 2.800 COAL

Charge    Velocity        StDev    ES
41.7 gr    2536 fps      23.91    60 fps
42.9 gr    2593 fps      16.63    46 fps
44.1 gr    2650 fps      20.19    49 fps
45.3 gr    2732 fps      15.06    33 fps
46.5 gr    NOT TESTED

A few comments about this test.  This was the first range outing for the PA-10 LR-308 pattern rifle.  I had no reference ammo to test for comparison velocities, and I failed to note in my source data that 2733 fps was achieved by Speer with a 22" barrel.  I should have expected 2670-2690 fps to be max load range.  The rifle failed to cycle or lock the bolt open on any load.  While this was later attributed to a mis-aligned gas port, at the time it was incorrectly attributed to the starting loads being light.  Primers looked comparable to the 7.62 NATO brass I have of the same headstamp that is not yet processed.

I will be doing some additional testing, with 44.5 grains as a max load for this bullet weight, which should result in a velocity of 2680 fps from a 20" barrel.

[The_Shadow]

The  MP-475 is similar WC 732...how close did it tract to actual published data?

[Johnnyreloader]

WC846 is available at redeyereloading.com

[sqlbullet]

Shadow, I have been unable to locate any WC 732 data.  If you have some or can point to a source, I would be glad to have it.

[The_Shadow]

Still looking for some data, but I did see some SR 4759 data in Speer #9.  If I find more I'll get back with you.

[The_Shadow]

I have searched through all of my data with no luck for the WC732 powder being used that is said to be similar to the Mid West Powders - 475
I have to wonder if the WC732 was only used for military contracts.  There is a picture of the WC732 in the Forensics data base and it is a flattened ball powder.

Sorry I couldn't find anything! 

[sqlbullet]

No worries.  I will forge ahead using IMR 4320 and 4064 data as rough guideposts and work up carefully from there.