Raising POI with bullet weight.

Raising POI with bullet weight.

This is a discussion on Raising POI with bullet weight. within the Defensive Ammunition & Ballistics forums, part of the Defensive Carry Discussions category; Hello everyone, I just got my S&W 3rd gen back from the smith after a new barrel was installed b/c the original had a heavy ...

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  1. #1
    Member Array Datsun40146's Avatar
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    Raising POI with bullet weight.

    Hello everyone,
    I just got my S&W 3rd gen back from the smith after a new barrel was installed b/c the original had a heavy land which caused the round to strike very low below my POI. Anyway, that problem was fixed with the new barrel however my rounds still strike about 1.5 inches low and 8-9 yards. I have heard that a heavier round such as 147 grain vs my usual 115 would raise up the POI. Is this true? Can I use 147 grain FMJ ammo to up my POI?
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    VIP Member Array Stevew's Avatar
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    Before I tried to correct POI at 9 yards I would want to find out what the POI was at 20-25 yards.
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    VIP Member Array dukalmighty's Avatar
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    I believe a heavier round will tend to drop faster,a lighter round has more FPS velocity and will shoot straighter longer,At 8-9 yards I don't believe it's going to make a lot of difference,If the gun is zeroed at 25 yards then it may very well shoot lower up close.One way to raise POI is to either replace rear sight with a taller one or use a shorter front sight,
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    Member Array Datsun40146's Avatar
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    I would think that a gun that is 1.5 inches low at 8 yards would be at least 4 inches low at 25. Why would the bullet drop and then raise? It doesn't make sense to me.
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    Member Array Emrah's Avatar
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    More recoil. Heavier bullets recoil more. More recoil means the muzzle rises more while the bullet is still in the barrel. The barrel is pointing a little higher when the bullet finally exits the barrel. This is a common phenomenon.

    Emrah

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    VIP Member Array hogdaddy's Avatar
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    Quote Originally Posted by Datsun40146 View Post
    I would think that a gun that is 1.5 inches low at 8 yards would be at least 4 inches low at 25. Why would the bullet drop and then raise? It doesn't make sense to me.
    It's called Trajectory
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    Quote Originally Posted by hogdaddy View Post
    It's called Trajectory
    I guess I'm confused too. How does it drop, then raise?

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    Distinguished Member Array kazzaerexys's Avatar
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    It doesn't drop first. The bullet is always below the sights as it leaves the barrel. Most pistols are zeroed in for 25 yds, which means POI == POA at that distance. That means with your sights level on target, the gun has to be shooting slightly upwards to overcome that initial difference in sight-to-muzzle height.

    Thus, your gun at the "zeroed" distance of 25 yards might be on target, or maybe 2" low rather than 4".

    As for weight affecting trajectory, the physicist in me says gravity is gravity and all things accelerate towards the earth at the same rate. That fall is determined solely by time of flight; velocity multiplied by time gives you distance covered.

    Thus it would seem that the slower round would cover less distance downrange in the time it takes to fall a given distance. I'd think the slower round would therefore be lower at any given point in the trajectory. Unless air resistance screws it all up, and I am no expert on ballistic coefficients.
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    Quote Originally Posted by Emrah View Post
    More recoil. Heavier bullets recoil more. More recoil means the muzzle rises more while the bullet is still in the barrel. The barrel is pointing a little higher when the bullet finally exits the barrel. This is a common phenomenon.

    Emrah

    We have a winner.

    Emrah is exactly right.

    It would seem that the heavier bullet would be lower on the target, but in fact it is opposite.

    This effect is very obvious on rifles. The heavier bullet will shoot higher every time...even though is seems backwards.
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    Member Array mtnclimber's Avatar
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    I have also noticed that slower bullets shoot higher at 25 yards. I have a 44 magnum that shoots right on at 25 yards. If I shoot 44 specials it shoots about 6 inches high. It is deadly on target hangers at indoor ranges! It seems the lower bullet velocity allows more time for the barrel to rise more in recoil before the bullet leaves the muzzle.

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    VIP Member Array Stevew's Avatar
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    Quote Originally Posted by Datsun40146 View Post
    I would think that a gun that is 1.5 inches low at 8 yards would be at least 4 inches low at 25. Why would the bullet drop and then raise? It doesn't make sense to me.
    Bullets have to travel in an arc. A bullet actually crosses line of sight twice. At 8 yards the bullet is still traveling up.
    If a barrel was held leval, rather than pointed slightly up, when fired the bullet would hit the ground at the same time as a bullet that was dropped from the same hight.
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    Member Array Datsun40146's Avatar
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    Huh that makes sense. I'll pick up some 147 grainers and see if I can move my POI around from the 115 grains. Also I'll try shooting at 25 yards. Its just SO hard to hold a group at that distance with a subcompact. I'll give it a go and let you guys know.
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    Emrah, Hotguns & mtnclimber are all right. Heavier bullets with slower velocity and usually heavier recoil allow more time in the barrel during muzzle lift causing the bullet to impact higher.
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    Absolutely, the heavier bullet. I was always somewhat disappointed to shoot 146 grain factory loads from my World War II Webley Mark IV .38/200 as they shot considerably lower than point of aim. I tried handloading some 200 grain round nose lead bullets and they grouped well and right where the sights looked.

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    VIP Member Array TedBeau's Avatar
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    Quote Originally Posted by Emrah View Post
    More recoil. Heavier bullets recoil more. More recoil means the muzzle rises more while the bullet is still in the barrel. The barrel is pointing a little higher when the bullet finally exits the barrel. This is a common phenomenon.

    Emrah
    OK, first off this makes sense to me, however I would like to point out a debate here a few months ago concerning recoil.

    The part of the debate that I was involved in was that I took exception to a statement that recoil is not felt until the bullet leaves the barrel. I said that according to newtons third law the recoil starts as soon as the bullet starts to move.


    http://www.defensivecarry.com/vbulle...perceived.html

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