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Thread: Handloading the 308 MX...

  1. #1
    Join Date
    Jan 2005

    Default Handloading the 308 MX...

    This time of year, here in the heart of Alaska, we don't get many opportunities to get out and shoot. Also, with the sun so low on the southern horizon, a solar triggered chronograph has only about 30 minutes in the middle of the day when it will work. Last week ends heat wave allowed an outdoor session and a chance to try out a new gun and cartridge, and to chronograph some loads I'd been working on.

    I was able to borrow a friend and his new Marlin in 308 Marlin Express. We shot a box of 160 grain Hornady leveRevolution (or however you say that) and a few different loads with the conventional flat point bullets and we single loaded a few spitzers.

    This caliber is a recent development from Hornaday manufacturing and Marlin Firearms. The case is based on the 307 Winchester cartridge case made for the angle eject model 94 Winchester. It is shortened .115" to allow the use of the longer spitzer shaped soft polymer tipped bullets and still maintain the Marlins maximum overall length of 2.560". From what I can determine this cartridge is pressure spec'ed at 47,000 psi, almost exactly where the old 300 Savage cartridge pressure limit is.

    In anticipation of the weekend shoot I had loaded a few of my best scientific guesses with a couple different powders. Lacking any available 308 Marlin Express brass, I ran 307 Winchester cases through the 308 MX full length sizing die. This 308 MX is not only shorter but has more taper and the shoulder diameter is reduced in the sizer. The now long neck of the reformed brass is trimmed to a length of 1.900".

    The 308MX is 1.9" long, with the length to the shoulder of 1.465" and to the neck of 1.660". The neck of the MX is also shorter than the 307. These dimensions are taken from the fired case with a more or less calibrated eye and a good dial caliper, so there is room for error. This case holds 48.2 grains of water when filled to the top. It will hold 46.2 grains of H4895 to the top and 42.4 grains of the same powder to the base of the neck. These numbers were taken from the reformed 307 brass, not the fired Hornady brass. I was not able to keep any of the hornady brass it left with the gun last Sunday. Reloaded of course.

    By comparison the unaltered and unfired 307 Winchester case capacities are listed compared to the new 308 MX.

    H2O full--H4895 full--H4895 neck
    56.6 grs.--50.5 grs--45.2 grs 307 Win---------------
    49.2 grs.--46.2 grs--42.4 grs 308 MX---------------

    I did not have a 300 Savage case to measure but it is very close in dimension to the 308 MX and loading data is very similar as is ballistic performance.

    I turned to my friends at Hodgdon's powder company for propellants for this newby and as always there are on the cutting edge of the new cartridge powder curve. I used a Sierra 150 grain round nosed .308" bullet which has always served me well in similar sized cartridges and also the Hornady 170 grain flat point bullet of .308" diameter also.

    The Hornady factory leveRevlolution ammo was 160 grains and was bought locally here in town. The advertised velocity for the 24" barrel Marlin was 2660 fps. The chronograph did not bear that out but it was about +18 degrees at the time of the shoot.

    This list below gives the velocities as taken from the handloads and the five factory rounds that went through the clock. I did not save a factory round to pull the bullet and weigh the powder charge as I usually do, all rounds were expended at the range. It would have been nice to see this magical powder that has been rumored to propel this streamlined plastic tipped bullet. Also I had read that the twist of the gun was to be 12" but it was 10" as we measured during the clean up exercise. In any case the accuracy was more than adequate for a lever rifle of this power range were it's use will likely be no more than 200 yards.

    Brass: Winchester brand 307 Win caliber reformed to 308 Marlin Express.
    Primers: CCI-200 large rifle.
    Bullet: Sierra .308" 150 grain round nose soft point.
    Powder: Hodgdons H4895, Varget.
    H4895 37.0 grs 2443 fps
    H4895 39.0 grs 2536 fps
    H4895 40.0 grs 2606 fps
    Varget 40.0 grs 2565 fps
    Bullet: Hornady 150 grain .308" spire point, single loaded.
    Varget 40.0 grs 2585 fps.

    Hornady .308" 170 grain flat nose.
    Varget 37.0 grs 2270 fps
    Varget 40.0 grs 2440 fps

    Hornady 160 grain spitzer soft tip LeveRevolution. 2571 fps.

    Overall this is a good performer. A much more decisive hammer than the older 30-30 and contained in essentially the same package.

    A real step forward in lever gun technology.
    Last edited by Murphy; 01-25-2008 at 17:39.
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