Bullet drop/rise question

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  • Mini14tac

    Ultimate Member
    MDS Supporter
    May 14, 2013
    2,146
    North County

    Guys, I get it. I was just trying to get the OP to be able to figure out what the problem might be. I did not run his 9mm through any ballistics tables to calculate the trajectory path.

    I usually sight my 9mm 16" PCC's at about 1" high at 25 to get them pretty close at 100. I'm using red dots or open sights.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    This diagram illustrates what he is saying:
    https://cdn.britannica.com/30/178630-050-D12B8390.jpg

    Calculate the mid range height and place a target at the mid range distance and the impact point should be that much higher than the zero if your zero is intersecting the descending arc of the bullet path however if the mid range impact is lower than the zero you are intersecting the rising arc of the bullet path. Either will be a "zero" at 50 yards but the down range results will be different.

    Fine for longer range zeros, but I defy you to set your rifle up to have a 50 yard zero with a descending path at that range.
     

    Scott's Gunsmithing

    Active Member
    Industry Partner
    Mar 21, 2010
    277
    Glen Burnie, MD
    The big factor is the height over bore. If your .22 has something traditional, like a 1.5" height over bore, then that drop should make sense. It's what I see on my marlin 795 moving from 50 to 100. Now with your ar, you're typically looking at something like a 2.7" height over bore. In that case, you're lobbing the bullet up at a greater angle to intercept the line of site at 50 yards, which could account for the different impact at 100.

    Bingo! An AR optic with a riser tends to sit higher above the bore axis than a typical 22 sport rifle.
     

    Neutron

    Ultimate Member
    MDS Supporter
    Nov 20, 2014
    1,531
    severna park
    Went to the range today and verified that it is indeed shooting higher at 100 yrs when zeroed at 50. I'm using a Firefield scope which is 2 1/2 " over the bore. 124 g fmj over 3.9g Bullseye.
     

    Tungsten

    Ultimate Member
    Jan 1, 2012
    7,230
    Elkridge, Leftistan
    Went to the range today and verified that it is indeed shooting higher at 100 yrs when zeroed at 50. I'm using a Firefield scope which is 2 1/2 " over the bore. 124 g fmj over 3.9g Bullseye.

    Are you changing any of the settings on the scope when you go from 50 to 100 yards? That may be consistently changing POI. Otherwise I have no clue how to explain a consistent 50 yard zero shooting high at 100 yards.
     

    Neutron

    Ultimate Member
    MDS Supporter
    Nov 20, 2014
    1,531
    severna park
    Yeah the scope is not the best, that's for sure. The adjustments only allow for 100 to 500 yds in 100 yd increments. I just leave it set at the 100 yd setting all the time since I'm not shooting past 100 yds. There are no settings for 25 or 50 yds. I guess I'll switch scopes next time and see what happens.
     

    Neutron

    Ultimate Member
    MDS Supporter
    Nov 20, 2014
    1,531
    severna park
    Switched scopes today and it behaved as expected. Zero at 50 and about3" low at 100. Zeroed at 100 and I'm leaving it there. I still have no idea why the other scope shot higher at 100 than it did at 50.
     

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