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  1. #1
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    Bullet drop

    I adjusted my EOTECH scope at 25 yds due to the limitations of the in door range. I am going to go to an out door range this weekend to test out my PS90 at 100 yards. What type of scope adjustment must I do, if any. Is there much of a bullet drop in the 5.7x28mm.


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    Re: Bullet drop

    Quote Originally Posted by spisam
    I adjusted my EOTECH scope at 25 yds due to the limitations of the in door range. I am going to go to an out door range this weekend to test out my PS90 at 100 yards. What type of scope adjustment must I do, if any. Is there much of a bullet drop in the 5.7x28mm.
    Depends entirely on the round used. Bullet trajectory also plays a major role of 'where the hit' will be.

    (Edited to remove "heavier bullet will hit the ground faster than lighter bulets" - Doh! Where was my head).

    If you zero your firearm at 25 yds using a 40 grain bullet, using the same zero, a 28 gr bullet will hit slightly lower. A bullet, regardless of weight, will fall to the ground at the same rate of speed. However, a 28 gr bullet will travel farther down range than the 40 gr bullet before it falls the same distance due to its increased velocity (lighter bullet, faster rate of travel). The reverse is true due to the 28 gr bullet flying at a flatter trajectory at a 25 yd zero as far as hit zone is concerned from 25 yds to 100 yds.

    Thus, unless you provide more specifics, it is impossible to give accurate data at what the projectile ballistics will be once the projectile leaves the barrel.

    Example: If you zeroed at 25 yds using a 28 gr bullet and try to adjust to 100 yds using a 40 gr bullet, you may encounter several inches of drop from one distance to another. If you zeroed at 25 yds using a 40gr bullet and try to adjust to 100 yds using a 28 gr bullet, the drop will be substantially less. Remember also that the bullet travels in an arc. It increases altitude at first then decreases altitude (this is because the barrel is in a slightly upward angle instead of being parallel to the ground) while the same force of gravity is working on the projectile.

    50 yards



    100 yards


    Best thing to do is to re zero at 100 yds and write down the changes made to you can zero back to 25 yds for indoor use. Whatever the outcome, the hit distance elevation change from 25 yds to 100 yds will still be on paper so adjust as you go.

    This does not even take into effect the distance of the sight elevation from the barrel line of sight. The above graphs were compiled using the 'stock' sighting systems.
    "We hang the petty thieves and appoint the great ones to public office." - Aesop

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    If your sight is far enough above the barrel, then having zeroed at 25 yards, you may find the POI is actually higher at 100 yards.

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    Thanks for the info.

    I am using the 5.7x28mm, SS197, 40 grain, blue tip

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    weight v gravity

    I thought gravity on earth was the same regardless of weight.
    heavy and light things fall at the same rate, its just the muzzle velocity and air resistance that determines the actual lengths of fall or am I wrong, Im not a physicist, just from high school.?

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    Re: weight v gravity

    Quote Originally Posted by mraxiomatic
    I thought gravity on earth was the same regardless of weight.
    heavy and light things fall at the same rate, its just the muzzle velocity and air resistance that determines the actual lengths of fall or am I wrong, Im not a physicist, just from high school.?
    +1

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    so I just went thru this exercise on my PS90 with a Burris fastfire mounted to the front of the rail.
    I had it zeroed at 25 but I didn't like the results, then I sighted it in at 100 but still didn't like the results, too much variance between 25yr and 150yd.
    so I went with the 50yd zero, I find that works best for the this type of rifle.

    I wish I had seen these graphs it would have made life easier.
    Basically now at a 50yd zero, 100yd POI is about 1.5" high, so I put the red dot about 1.5" lower than where I want it to hit.
    Inverse for a 25yd POI, I just put the red dot about 1.5" higher than where I want it to hit.
    My eyes aren't good enough to see a target at 150 without contacts or glasses which I don't wear at the range, but it's like 1/2" or so low.

    all on SS197

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    Quote Originally Posted by reapur
    I wish I had seen these graphs it would have made life easier.
    We've been posting them on here for years.

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    Re: weight v gravity

    Quote Originally Posted by mraxiomatic
    I thought gravity on earth was the same regardless of weight.
    heavy and light things fall at the same rate, its just the muzzle velocity and air resistance that determines the actual lengths of fall or am I wrong, Im not a physicist, just from high school.?
    Don't know where my head was that morning. Stated something in the first sentence which was wrong and then stated the accurate fact almost immediately after. So for clarity, I removed the offending statement in the original post.
    "We hang the petty thieves and appoint the great ones to public office." - Aesop

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