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What is the effect of velocity on POI?

Discussion in 'Shooting Related Threads' started by McHale1, Aug 3, 2013.

  1. McHale1

    McHale1 TS Member

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    Is it just my imagination or does my POI become lower with a higher velocity load? I have been shooting 1 1/8 oz. factory loads at 1,145 fps and yesterday I shot four boxes of AA extra light 1 oz. at 1,300 fps. It sure seemed like my gun was shooting flatter with the faster shells. What say you experts, please?
     
  2. hmb

    hmb Well-Known Member

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    Yes, you are right. This is do to muzzle rise, the shell with more speed gets out of the barrel sooner. The slower shells payload takes longer to get out of the barrel and the barrel is pointed up more do to muzzle rise from recoil. HMB
     
  3. zzt

    zzt Well-Known Member

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    ditto.
     
  4. texasbilly

    texasbilly Member

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    What you noticed with your shotgun is seen in rifles and handguns too. Lower velocity ammunition tends to shoot to a higher POI; light weight, high speed, ammunition tend to shoot to a lower POI. That's why you must re-sight your gun when you change ammunition.

    Case in Point: My S&W 38 Special was shooting 12" high at 25 yards with standard velocity rounds(yes, 12" high). I was frustrated with the revolver, and thought about sending it back to the factory. Before I did, however, I loaded some Sierra 125 gr bullets to +P velocity, and now the little gun prints point of aim. Quite a change.
     
  5. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    McHale1, did you measure from POA to the centers of patterns, in terms of inches?? If so, what were those numbers?

    HAP
     
  6. 391 shooter

    391 shooter Well-Known Member

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    What is the effect of velocity on POI?

    The shot stream gets there faster.
     
  7. JT 27

    JT 27 Member

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    Ballistics fall in to the laws of gravity (physics). Be it pellets or bullets, the mass starts to fall immediately when it exits the barrel. The mass would hit the ground (assuming level) at the same instant if dropped or shot. It would just hit further down range. Aiming or shooting high will alter that time. If you shoot 1100 fps or 1450 fps the mass will travel further, if shot flat, but will take the same amount of time to hit the ground.
     
  8. likes-to-shoot

    likes-to-shoot Well-Known Member

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    I've never noticed any change between 1145 fps to 1250 fps and any velocity in between. I shot the different speeds from the 16 on back.

    I'm not saying there isn't a difference but I don't think a human could consistently tell any difference.
     
  9. birdogs

    birdogs TS Member

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    All projectiles fired from any gun begin to drop the instant they leave the barrel. The line of sight is above the barrel so we must elevate the barrel so that the projectile crosses the line of sight, traveling in an arc. The projectile thus crosses the line of sight traveling in an arc above it. All this while, gravity is working to pull the projectile back to earth. Eventually, the projectile again crosses the line of sight, this time traveling from above it to below it. The point where they cross this second we call the Point of Impact.

    A faster moving projectile will have a lower arc (trajectory) and will cross the line of sight farther from the muzzle than a slower projectile. Thus the POI will be slightly lower anywhere along the line of trajectory.
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    BD, why will "A faster moving projectile . .. l have a lower arc (trajectory) and will cross the line of sight farther from the muzzle than a slower projectile. "

    This is not a challenge to your post, just a question of why?

    Neil

    In answer to the original question, shotgun, as do all other firearms, shoot "groups," that is, not to a point but to a "place."

    When I compared the POI of Extra-Lites and Super-Handicaps at 13 yards, ten shots of each, the "groups" of each were far larger than any difference between them. In other words, a particular POI could have been a member of the "fast" groups or the "slow" group and there was no way to tell, looking at a particular shot, whether the shell that produces it was "fast" or "slow." Remember, this is off a rest, carefully done, with the target not moving.

    Based on my experiment, I think it is very, very unlikely that a difference could be detected when the target is moving and farther away.

    Neil
     
  11. hmb

    hmb Well-Known Member

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    You did not answer the original question. His question is for a hand held gun, not one shot from a rest. HMB
     
  12. Neil Winston

    Neil Winston Well-Known Member

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    Well, HMB, since a rest is the only way to tell where a gun is shooting, I thought I was being nice.

    I take it your point is, however, that guns shoot differently from a rest than hand-held. Remember, these are not pistols, they are shotguns. My question is how do you know they shoot differently from a rest and hand-held? What evidence are you basing this on?

    Remember, this is not a general question, but a specific one. What evidence can you cite that light shells and 1300 fps shells respond in terms of their POI when shot off a rest and when shot off-hand?

    When I tested them off a rest the groups shot by shotguns obscured any difference that might or might not have been there. How do you get around the "group" problem with shotguns?

    Neil
     
  13. Straight50

    Straight50 Member

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    When you sight a rifle in, to be ON TARGET at a 100 yards, somewhere between the target and the muzzle the bullet will be above the muzzle/target at some point due to the trajectory of the bullet. A mass of shot will do the same thing if sighted in for a point of impact of let's say 40 yards! Am I correct, or off base?
     
  14. Neil Winston

    Neil Winston Well-Known Member

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    "When you sight a rifle in, to be ON TARGET at a 100 yards, somewhere between the target and the muzzle the bullet will be above the muzzle/target at some point due to the trajectory of the bullet."

    Will it? Doesn't it depend on the frame of reference?

    From the point of view of the line of the bore, the bullet (or shot) falls all the time. From the point of view of the position of the muzzle in space, the bullet goes above it.

    With shotguns and 40 yards, "it depends."

    1. It may shoot flat out the gun (the bore being horizontal) and so the shot is always under the muzzle, always under the line of the bore.

    2. It may shot a little high. Say, geometrically, 3.3 inches high at 40 yards. In that case the shot will rise above the muzzle but fall back to flat at 40 yards under the influence of gravity.

    3. The gun may shoot way high. Say a foot, geometrically, and so the shot will be above the muzzle (in space) virtually all the time, and hitting eight or nine inches high and so never getting back down to muzzle level at all.

    Neil
     
  15. mette56

    mette56 Well-Known Member

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    Growing up I did alot of dove hunting. After years of experience, it seemed to me that the larger and heavier shot size retained its velocity at a further distance compared to the lighter shot sizes. I.e., 8 shot vs. 6 shot. If shooting 8 shot at doves, my kill range was less than if shooting 7 1/2's or 6's. Would that result (if it was a true result) be because of shot size/weight, shot size impact or what?

    and does this effect, if real, result because of velocity?..energy considering shot size?..or what? Never noticed a difference in POI, but wouldn't have being a teenager shooting a Rem. 870 16 ga.

    milt
     
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