375 Allen Magnum first long range accuracy test, 510 Allen Magnum gets to play too...

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Fiftydriver, Feb 14, 2008.

  1. Fiftydriver

    Fiftydriver <strong>Official LRH Sponsor</strong>

    Jun 12, 2004
    Yesterday was not a great day here in Montana, pretty much a blizzard all day. My dad came up and formed up a bunch of brass for customers rifles but was unable to actually fire them because of the weather so I told him to come back up this morning and he could fire them up and then if we had time we could run out and do a bit of shooting.

    Today was a MUCH better day, a bit windy but sunny and around 35 degrees when we headed out over lunch to do some shooting. Main goal was to do some testing with the 375 Allen Magnum. I had done some quick load development and settled on the following load:

    New Jamison cases
    350 gr SMK
    144.0 gr Retumbo
    4.315" OAL
    3245 fps average

    I had taken the rifle out on my 100 yard range, shot three shots which printed at 0.388" ctc. Made a scope adjustment to zero at 100 yards and confirmed with two shots which both landed inside the 1/2" open center of my 100 yard target squares.

    We packed up and drove out to our favorite shooting place. Set the rifle up and Dad got on the rifle and started looking for a good target rock up on the distant hillside.


    Dad found a good target rock, roughly 25" long and 12" tall. He talked me into its location and I hit it with the Swari and got 1235 yards back several times. Plugged the numbers into my palm using a BC of .800 which was just a guess to be honest. The dial up was 24 moa for 1235 yards.

    Told Dad the dial up and he cranked it in. I then told him to shoot three shots at the rock and see where the shots landed. The wind was pretty strong but coming from our back. My only concern was down drafts as the wind was coming down on top of us so we tried to time things between the gusts which were pushing around 20 mph at times. Consistant winds in the 8-9 fps range did not really concern me much for this test.


    Here is a pic of Dad lining the big 375 up on his selected target rock, roughly coyote size.


    MUD IN THE AIR!!!! In the center of this pic you can see the target rock. Roughly 1 minute above the rock you can see the eruptions of mud from the three impacts from the big 375 AM. For the first three shots at 1235 yards, not to damn bad. The first and third shot landed in the same crater, the second shot was slightly higher producing a group well under 1 moa measured using the NP-R1 reticle. In fact it was a bit under 3/4 moa. The recommended dial up was roughly 1.5 moa to much so from a 100 yard zero, it took 22.5 moa to be dead on at this 1235 yard range.

    We know that because we let the barrel cool, I told dad to take out 1.5 moa from the elevation and he placed three shots hard on rock. First and third again were dead center impact, just inches apart. The second was on the right third of the rock. Still well under 3/4 moa for total group size.

    From this inital long range test, it appears that the BC of this bullet from actual bullet drop is in the low .8 range. Probably around .820 but again, there needs to be alot more testing before this will be a known value to use for long range precision shooting on big game.

    There was no need for me to shoot the rifle, Dad did very well and obviously the combo will be a shooter. Its not quite as flat as the 338 AM but barrel temp was noticably lower which will lend to longer barrel life no doubt.

    Next up, the big 510 Allen Magnum needed some air time. It has been a while since I shot this big girl so I figured it was time to warm its barrel up some. The load I am using in this rifle is relatively mild driving the 750 gr A-Max to around 2700 fps. It is comfortable and is just a bit higher then what is comfortable with the standard 50 BMG.


    Here is Dad on the big 510 Allen Magnum. I shot the rifle first and had no idea where it would be hitting as I had pulled the scope and remounted it earlier this winter. I bore sighted the rifle at the same target rock. Looked like there was plenty of vertical adjustment to get at least close to the rock.

    I lined her up, first shot landed right on the bottom post of the reticle making the adjustment easy. Dialed up the difference and shot anther one. which hit the rock. Shot one more and hit it again.

    We let the barrel cool and then Dad took three shots. His three all landed on the right edge of the rock. In fact, In the pic above of the rock, you can see the mud splatter to the right of the rock from one of his shots. The other two were just on the rock on that edge.

    All in all, not to bad. Both rifles have alot of work ahead of them as far as getting them tweaked and tuned with a reliable drop chart but for shear long range consistancy, both did extremely well.

    Much more to come!!!

    Now, back to work!!!

    Kirby Allen(50)
  2. ss7mm

    ss7mm Writers Guild

    Jun 11, 2005
    Ah yes......spring time in Montana.:):)

    Now I see who has to sit outside in the cold and do all of the testing.:rolleyes: You fire one shot, hand the rifle to Roy and then drink hot coffee and take pics while he does all of the work.:)

    Looks like the 375 is showing promise. Very interesting, keep us posted and tell Roy to dress a little warmer if he's going to have to do all of the "work";)

  3. landcbeitner

    landcbeitner Well-Known Member

    Jan 13, 2008
    Now that looks like fun. Great report. My smith is interesting in build something simular to the 375 AM for himself. Looking forward to more range reports from you guys!
  4. wildcat

    wildcat Well-Known Member

    Jul 16, 2005
    I feel sorry for the Rockchucks in Montana this year. It sounds like your ready to make the 3000 yard club. I am betting you get a Rockchuck at 3000+ this year. Look forwardto hearing about that.

  5. magicofmt

    magicofmt Well-Known Member

    May 9, 2005
    With that big muzzelbrake, better watch those truck windows. Being that close, I thought it would take that back window out??

    Great report, can't wait to do that long range testing with my 338 AM.
  6. comfisherman

    comfisherman Well-Known Member

    May 2, 2007
    Always a fun read

    Always love to see picuters of your rifles, especially the big 510.
  7. jimbo300

    jimbo300 Well-Known Member

    Sep 2, 2007
    Awsome pics and report. That BIG 510 is a real thing of beauty. Your posts always make good dream material. Once again love those pics.
  8. Boss Hoss

    Boss Hoss Well-Known Member

    Nov 10, 2005
    Sure beats the hell out of what I did yesterday!!!!!!
  9. Buffalobob

    Buffalobob Writers Guild

    Jun 12, 2001
    Is your Dad wearing prescription sunglasses?
  10. grit

    grit Well-Known Member

    Mar 23, 2005
    I think, somewhere along the road, you made a good career move!