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  1. #1
    Machine Gunner DenverGP's Avatar
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    Default Ballistics difference from 55gr M193 vs 77gr SMK .223

    While preparing some ballistics data for the bailey 2-gun match, I ran ballistics for both my 77gr SMK ammo and standard 55gr M193 ammo.

    I don't have access to a chrono, so I'm just using velocity data I gathered from the net...

    Starting with the rifle zeroed for 100 yards, I was surprised that the ballistics calculators show I need to come up less for M193 than for the heavier 77gr match ammo. I assumed the heavier bullet would shoot flatter.

    For M193 I'm using a velocity of 3200fps (from my 18" barrel), the calc shows I would need to come up 11.6 MOA.

    compared to the 77gr, I'm using a velocity of 2700fps, the calc shows I would need to come up 14.9 MOA
    'Unless a law-abiding individual has a firearm for his or her own defense, the police typically arrive after it is too late. With rigor mortis setting in, they mark and bag the evidence, interview bystanders, and draw a chalk outline on the ground' - Judge Benitez , 2019, Duncan v. Becerra.

    'One of the ordinary modes by which Tyrants accomplish their purpose without resistance is by disarming the people and making it an offense to keep arms.' Supreme Court Justice Joseph Story, 1840.

  2. #2
    Ammocurious Rucker61's Avatar
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    What distance?

    Edit: look at the windage advantage for the 77 gr.
    Last edited by Rucker61; 09-09-2019 at 12:47.
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  3. #3
    Machine Gunner DenverGP's Avatar
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    I was only going out to 600 yards (max i'll be shooting for the match).

    I did see that the windage doesn't shift as much with the heavier bullet, for a 10mph 90 degree wind at 600 yards, it's showing 4.6moa for the 77gr, and 5.3moa for the 55gr.

    Doing the charts out to 1000, the 77gr always has more drop. It looks like @ 700 yards both bullets would be about the same speed, around 1615fps. At further distances, the 77gr carries the speed better, so it's faster than the 55gr further out than 700 yards.

    I was just surprised, I thought I was using the 77gr to get a flatter trajectory at 600 yards. I suppose the 77gr SMK bullets should be more accurate, so I'll keep using them at longer range.

    I'll start running some number for some of the bullet weights in between 55gr and 77gr. I just assumed the heavier the better, but maybe not so much at 600 yards.
    'Unless a law-abiding individual has a firearm for his or her own defense, the police typically arrive after it is too late. With rigor mortis setting in, they mark and bag the evidence, interview bystanders, and draw a chalk outline on the ground' - Judge Benitez , 2019, Duncan v. Becerra.

    'One of the ordinary modes by which Tyrants accomplish their purpose without resistance is by disarming the people and making it an offense to keep arms.' Supreme Court Justice Joseph Story, 1840.

  4. #4
    Grand Master Know It All CS1983's Avatar
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    Heavier/higher BC is better if you are trying to buck wind more and and be more accurate. But the lighter bullet is going faster initially, so it has an advantage as far as drop out to a certain point. But drop isn't everything.

    Wind
    Terminal ballistics
    Flight characteristics and accuracy
    etc.

    I'm not sure why you thought 77gr would be flatter shooting, though.
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