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Thread: Nice morning at the range; mod POI change ?

  1. #1

    Nice morning at the range; mod POI change ?

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    Had a pleasant and educational morning experimenting with my new mod down at the range this morning.

    Was interested to find out that the difference in POI for mod off / mod on is a full 6cm at 100yards; so using the mod means the bullet strikes 6cm higher than it would without for the same zero. No change in the horizontal plane so I'm guessing this is down to a reduction in recoil. This is in 6.5x55.

    It seemed to me to be quite a large change in POI and more than I was expecting; is this a typical shift ?

  2. #2
    All the mods I have used have shifted the POI downwards, but that's only 6 mods on 3 rifles.

    The shift with a T8 was 6" and with a Spartan, 3".

    It made sense to me as the Spartan weighs less than the T8.

    But your POI shifts upwards, well as they say across the pond, go figure!
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  3. #3
    I agree, it surprised me. Instinct told me that the POI should go down.

    Extremely consistent results though over about 40 rounds with the mod coming on and off regularly.

  4. #4
    You haven't got one of those titanium mods that are so light the lift the muzzle, have you?
    "Nonsense! They couldn't hit an elephant at this dista.....................".

  5. #5
    Aluminium. It is an Atec CMM4; pretty light at about 220g if I recall correctly.

    ​Wish I'd paid more attention in physics...can't figure out the logic.

  6. #6
    More likely its the weight of the mod changing the barrel harmonics that causes the majority of the change in POI (which could be in any direction) but it's also not uncommon for a mod to increase velocity slightly by acting like a barrel extension so that could have a tiny bearing on it too.
    Last edited by csl; 20-07-2013 at 20:18.

  7. #7
    Quote Originally Posted by csl View Post
    More likely its the weight of the mod changing the barrel harmonics that causes the majority of the change in POI (which could be in any direction) but it's also not uncommon for a mod to increase velocity slightly by acting like a barrel extension so that could have a tiny bearing on it too.
    +1, on harmonics. Barrel compensation can be upward as well as downward.
    Adding the mod will have adjusted the 'harmonics wave' (energies released on the shot) barrel 'up' as the shot leaves the moderator muzzle.
    There is a lot written about this viz a viz WW2 Mauser vs. Enfield - and we all know you've got a Gerry rifle!
    I'd stiil have come to spot for you ;-)

    PS Glad that mod has worked out for you, I'm very happy with mine
    Last edited by RickoShay; 20-07-2013 at 20:56.
    "There comes in the dead of night a hand of cold steel that plucks the German sentries from their posts"
    WSC 1942

  8. #8
    Ah, got it, makes sense now. Knowing 'why' will give me more confidence in the kit.

    RS - you're welcome to spot anytime ! By the way, best group was 4 touching for under 1cm. That was the (unmoderated) 30.06 though; the old 6.5x55 has a deadly rival !

  9. #9
    Excellent shootin' J, be good to see that 30'06 in action. Do you take the case with you in the field? Tis very smart..
    "There comes in the dead of night a hand of cold steel that plucks the German sentries from their posts"
    WSC 1942

  10. #10
    Quote Originally Posted by csl View Post
    More likely its the weight of the mod changing the barrel harmonics that causes the majority of the change in POI (which could be in any direction) but it's also not uncommon for a mod to increase velocity slightly by acting like a barrel extension so that could have a tiny bearing on it too.
    How does that work then?

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