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Author Topic: MP 475 Powder  (Read 5149 times)

sqlbullet

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MP 475 Powder
« on: April 01, 2020, 11:55:19 am »
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? 
Utah

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    coelacanth

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    Re: MP 475 Powder
    « Reply #1 on: April 01, 2020, 04:59:05 pm »
    I have no experience with it at all.  I don't load for the .223 / 5.56 and have typically used ball type powders for the heavier bullet .308 loads - 165 grain Sierras over Winchester 748 for the bolt action hunting rifle.  Maybe somebody else will weigh in.   :hmm
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    sqlbullet

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    Re: MP 475 Powder
    « Reply #2 on: April 03, 2020, 04:07:18 pm »
    Well, I have 32 lbs on the way.  I also grabbed 16 lbs of their MP842 (WC-842) and 16 lbs of their MP-500 ("Similar to Reloader-15").

    I will post about the results once I get a chance to work up some loads.
    Utah

    ksuguy

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    Re: MP 475 Powder
    « Reply #3 on: April 03, 2020, 05:04:20 pm »
    I'm thinking I might actually start using the Dillon 550 I bought 15 years ago.    Got a couple of jugs of Varget I bought back then too.   

    Should work ok for some .308 loads.   
    Kansas

    sqlbullet

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    Re: MP 475 Powder
    « Reply #4 on: May 05, 2020, 11:23:30 am »
    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.
    Utah

    coelacanth

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    Re: MP 475 Powder
    « Reply #5 on: May 05, 2020, 05:12:21 pm »
    Good write - up.  Thanks for sharing it with us.  I like your approach to the problem(s) and agree with your conclusions.  As I noted before I have no experience with this powder and its always good to get more info on something I may have to use at some point.   :thumbup1
    Arizona" A republic, if you can keep it."

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    Grant

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    Re: MP 475 Powder
    « Reply #6 on: May 07, 2020, 08:12:31 pm »
       Nice writeup.  Never even heard of 475 but always good to know more options.
    Montana"I’d say the worst part of all this is the feeling of betrayal,           but I’m betting the part where they break in here and beat us to death might be worse.”

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