Looking for the numbers - gun movement translating to accuracy on the target

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by rem.xp100, Apr 11, 2010.

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  1. rem.xp100

    rem.xp100 Active Member

    Mar 30, 2005
    I came up empty on a search but think the info might be here someplace.

    I am looking for the actual figures of rifle movement as related to accuracy on the target.

    For example: Gun movement of .001 inch (or so many tenths of a degree) would translate to ??? at 100 yards at the target.

    I could work the math out but I am sure someone here has already done it.

    Thanks in advance,

  2. RockZ

    RockZ Well-Known Member

    Mar 10, 2006
    I once read that gun movement of .001inch results in 1/4
    deviation on the target

    GNERGY Guest

    I was told a long time ago by a benchrest shooter that .001 inch movement equals 1 inch at 100 yds.
    It would also depend on the space between point of movement. I recently was sighting in a rifle that I had a .010 inch shim under the rear scope base, and ran out of adjustment. I removed the shim and my point of impact at 100 yds moved 10 inches. I ended up using the different Burris offset ring inserts to get it adjusted.
  4. Mikecr

    Mikecr Well-Known Member

    Aug 10, 2003
    No where near the information needed..
    For one, the 'movement' would need to be defined in amplitude of each X,Y, &Z.
    The recoil speed would also have to be taken into account, as this relates to potential bullet position per time. This also varies with cartridge & load.
    And then there is the challenge of validating any of it..

    BR shooters generally shoot free recoil, and their guns move. But they don't throw shots as implied here. So consistency is another factor pretty much undefinable.

    In otherwords, you shouldn't solicit clan lore as meaningful here.
  5. groper

    groper Well-Known Member

    Sep 2, 2008
    well i thought it would be a simple as 1 MOA (minute of angle = 1/60th degree) of rifle barrel angle movement = 1 MOA of movement on the target (= 1in @ 100yds)?

    Or 1 Milliradian of barrel angle change = 1m @ 1000m bullet impact change.

    why does it need to be anymore complicated than this?

    if your looking for what it means in terms of muzzle distance movement instead of barrel angle movment, simply scale it down to the barrel length. So if you move the muzzle by 1 MOA and say your barrel is 30in long.
    1 MOA = 1in @ 100yds
    = 1in @ 3600inches
    = 30/3600 (barrel length divided by distance)
    = 0.0083 inches at muzzle = 1MOA = 1inch at 100yds.
    Last edited: Apr 12, 2010
  6. rem.xp100

    rem.xp100 Active Member

    Mar 30, 2005
    groper - that's pretty much what I needed. Maybe an explanation as to what I want the information for would have helped the responses.

    I am getting frustrated talking to shooting friends about guns and group sizes: i.e. friend "x" who is fairly new to rifles (not guns but rifles) works on a load and goes to the range and shoots his first ever 1/2 inch group with a gun I built for him (light barreled hunting rig in 300WSM). Off the bench with a bi-pod. Great - happy as a ....

    Now back to the range another day and he shoots over an inch - my phone rings with "what do you think could be wrong with the gun? It's shooting all over the place."

    Well he's a very good friend so it's hard to just throw out there that perhaps the fact that you have only ever shot one 1/2 inch group in your life might make you think it is operator error

    SOOOO, I hint about things like "do you realize how little it takes to open up a group from a half to one inch? How tiny the movement really is? Or the fact that you shot the good group on a calm day and this on a windy day which can open it up that much. The fact that bi-pods can react differently when on different surfaces like a wood bench versus concrete - or you can torque the legs while positioning and then they "jump" when you shoot. Or maybe the original group you shot being only 3 rounds was actually a fluke - should have shot 5 rounds at least. Or your loads aren't that consistent. And on and on...ect. ect. ect....

    Just looking for a pleasant way to let him know it usually isn't the gun at that point.
  7. ovastafford

    ovastafford Well-Known Member

    Oct 23, 2009
    Did you ask him if he had drank some coffee, mountain dew, caffeine, etc...... I dont know how many people know this but it will really screw you up. My buddy and I went shooting the other day and his gun was shooting all over the place. Wasn't even close to where it was the day before. It was shooting 2-3" groups way off, when on the prior day was consistently shooting .5 moa. Finally after he had messed with his scope and shot probably 4 groups he had me shoot it. Three shot in the same hole! He couldn't believe it. From now on I wont drink coffee or anything with caffeine in it before shooting. Besides everyone has a bad day, it just happens.....