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Thread: Shooting theory question

  1. #1
    Boolit Mold
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    Shooting theory question

    So I was visiting a friend today and we started playing around with one of those laser trainers to see who could get the fastest draw, fastest "reload", etc. I started noticing that standing 10 yards away my semi auto was shining the laser about 2" high when the sights were held on the bullseye. Well that got me curious so I moved closer and eventually I determined that it was shining dead on at about 2.5 yards. It was low if I moved closer and higher if I moved further away.

    As a mental exercise I tried to remember a couple ballistic calculations that I had learned years ago. I eventually determined that if that trend continued, my laser would shine almost 6" high at 25 yards and about 1 foot high at 50 yards. But here's the problem: assuming an average speed of 1150 fps, a 9mm will only drop a little under an inch at 25 yards. But...I have no problem hitting the target when i'm shooting live ammo, and my point of impact is damn near perfect with the point of aim. So I must have done something wrong. I just can't seem to figure out the issue. Any help?

    Sorry for the overly technical question, I wasn't sure which board was most appropriate but I figure someone must know

  2. #2
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    Those things might not line up perfectly at a given range that jives up with your bullet drop & 'zero'.

    You'd need to live fire it to check. But I wouldn't expect them to be as accurate/on target as a high end bore sight.
    See where the dot is in relation to your sight picture at the different range, and shoot accordingly to find where its zeroed,

    or more nearly where the two points are in a bullet's arc of flight that 'point of aim' is the same as 'point of impact'.
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  3. #3
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    Sights at most can be dead on at two ranges. With sights above the barrel, the bullet will rise above the line of sight at some point on the trajectory, at that point the sights are dead on. Eventually the bullet will fall below the line of sight and will be dead on again. With a pistol more so than a rifle the barrel moves between the time you press the trigger and when the bullet leaves the barrel. With a centerfire pistol the barrel will be pointing higher when the bullet leaves the barrel.

    You don't say where the laser is but I am guessing it is in the barrel. If you take it out spin is 90 or 180 degrees and put it back in does it shift relative to the sights? I wonder if it is perfectly centering in the bore.

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  4. #4
    Boolit Mold
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    Yes but with the laser trainer the sights will only be right on at one point, because it essentially simulates a bullet with no drop. That point seems to be right at about 2.5 yards. And yes the laser cartridge goes in the chamber. It has a couple of O-rings that hold it relatively tightly and keep it fairly accurate. I have taken it out and put it back in several times and never noticed a difference in where it was shining. I'm sure it's not as accurate as a high quality bore sight, but its not bad.

  5. #5
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    I'm not the sharpest tack in the sewing box but to my understanding, boolits/bullets don't start falling for 25 to 50 yards.

    Question 2 why would you even need sights at 2.5 yards? much less site in at that distance

  6. #6
    Boolit Master


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    Unless you have hands of steel, your grip is not a solid rest for the pistol. Your point of impact will change between a tight or loose grip.

  7. #7
    Boolit Mold
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    This wasn't exactly a project of practicality. I know there's really no use of using sights at that short of distance, and that the laser is not going to do what a live round will do. I'm just trying to figure out why my math doesn't add up. The laser shoots 2.5" high and the bullet will only drop less than 1/4" inch at that distance. Yet I hit dead on during live fire. So clearly i've done something wrong in my theory and I just can't figure it out

  8. #8
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    Quote Originally Posted by The1970's View Post
    The laser shoots 2.5" high and the bullet will only drop less than 1/4" inch at that distance.
    Your math will only work if the sight plane is 100% level and parallel to the center line of the bore.
    The laser doesn't know how to compensate for that, or bullet drop.

    Try laying the gun down flat on a table or in a rest, turn on the laser, and put a straight edge over the sights as they are aligned.
    Or, look through/over the sights with another laser.
    I'm guessing you'll see the difference then.
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  9. #9
    Boolit Man

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    LASERs are effectively a straight line while bullets travel in an arc. There are two points where the bullet crosses the line of sight. The first point is near the muzzle and the second point is at the target.
    This is an example of 45ACP courtesy of https://www.federalpremium.com/ballistics-calculator
    It shows a zero at 7 ft and 49ft
    Click image for larger version. 

Name:	Bullet Arc.jpg 
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ID:	272557
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  10. #10
    Boolit Grand Master


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    You aren't wrong, my calculations also show a 9mm bullet will drop around 1" at 25 yards. My question though, is why do you think you pistol and the laser gun would be sighted in the same way? Your pistol is not zeroed at 2.5 yards, or you would be shooting over everything.

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    Be sure to include math formulas for your trigger pull and recoil/flinch
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  12. #12
    Boolit Master

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    The last place I would expect the bullet to hit is where a bore sighter or laser are pointing. barrel harmonics, recoil, grip, flinch, etc all come to play.

    That is we zero rifles and pistols instead of relying on a laser in the chamber or muzzle. They will get you close, but i can almost guarantee that the bullet leaving the muzzle isn't following the laser path, discounting drop.

  13. #13
    Boolit Master

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    If you look at a revolver, a lightweight. snubnose, the barrel doesn't point toward the bullseye, but actually points downward by an observable amount.

  14. #14
    Boolit Mold
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    Quote Originally Posted by megasupermagnum View Post
    You aren't wrong, my calculations also show a 9mm bullet will drop around 1" at 25 yards. My question though, is why do you think you pistol and the laser gun would be sighted in the same way? Your pistol is not zeroed at 2.5 yards, or you would be shooting over everything.
    Right. I know it's not zeroed at 2.5. It's more like 25. I guess my question is where does the laser differ from a theoretical "no gravity" bullet. Surely a bullet that does not experience the effects of gravity would not change my "zero" point to 2.5 yards, so why do I see that with the laser? I know that barrel harmonics and grip all come into play but I wouldn't expect that large of a difference.

    For example, my math says a 9mm will drop 0.81" at 25 yards. So with the laser i.e. a "no gravity" bullet, I would expect to see it "hit" almost exactly .81" high. Instead it "hits" about 6 inches high. That's not a small difference at such a short range. I'm by no means the best shot around but I can certainly tell the difference between 3/4" and 6 inches.

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    Quote Originally Posted by Conditor22 View Post
    I'm not the sharpest tack in the sewing box but to my understanding, boolits/bullets don't start falling for 25 to 50 yards.

    Question 2 why would you even need sights at 2.5 yards? much less site in at that distance
    Not quite true The boolit/bullet starts "Dropping" as soon as it leaves the end of the barrel due to gravitational pull. Because of the energy imparted from the gas of the powder burning the path the bullet takes is that it rises over the straight visual line and then fall below that visual line. All through that arc the bullet follows, it is being puled by gravity.
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    Quote Originally Posted by The1970's View Post
    SNIP>>>

    I know that barrel harmonics and grip all come into play but I wouldn't expect that large of a difference.
    how much did your Math tell you, to expect?
    Last edited by JonB_in_Glencoe; 12-04-2020 at 12:24 PM.
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  18. #18
    Boolit Master Win94ae's Avatar
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    I usually sight my handguns in at 65 yards with my preferred load. So it hits POA around 7 yards, then is 4 or so inches high at 30 yards, hits POA at 65 yards, then is 4 or so inches low at 100 yards.

    I have 2 38 specials with fixed sights that hit POA around 7 yards, but climb higher and higher as the range gets longer. By the time I get beyond 150 yards, I can't shoot them well enough to see at what range the round hits back to POA.

    When I sight my handguns, I take note at what height my POI is when it comes back down, it will always be close enough at 7 yards.

  19. #19
    Boolit Master Win94ae's Avatar
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    Quote Originally Posted by Brass&Lead View Post
    LASERs are effectively a straight line while bullets travel in an arc. There are two points where the bullet crosses the line of sight. The first point is near the muzzle and the second point is at the target.
    This is an example of 45ACP courtesy of https://www.federalpremium.com/ballistics-calculator
    It shows a zero at 7 ft and 49ft
    Click image for larger version. 

Name:	Bullet Arc.jpg 
Views:	44 
Size:	98.4 KB 
ID:	272557
    Actually, that is yards, not feet.

  20. #20
    Boolit Grand Master


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    Quote Originally Posted by The1970's View Post
    Right. I know it's not zeroed at 2.5. It's more like 25. I guess my question is where does the laser differ from a theoretical "no gravity" bullet. Surely a bullet that does not experience the effects of gravity would not change my "zero" point to 2.5 yards, so why do I see that with the laser? I know that barrel harmonics and grip all come into play but I wouldn't expect that large of a difference.

    For example, my math says a 9mm will drop 0.81" at 25 yards. So with the laser i.e. a "no gravity" bullet, I would expect to see it "hit" almost exactly .81" high. Instead it "hits" about 6 inches high. That's not a small difference at such a short range. I'm by no means the best shot around but I can certainly tell the difference between 3/4" and 6 inches.
    Why wouldn't you believe recoil is the cause? By my calculations, with a 4" barrel, if you move the muzzle .027", you will move 6" at 25 yards.

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