ballistics question

Discussion in 'Rifle Talk' started by wired, Jul 12, 2005.

  1. wired

    wired Guest

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    Okay, ballistics gurus, I need a quick hand here. I finally found a local gunsmith that could install the front sight ramp on my .308, and I wanted a little advice on something. I am going to sight the rifle in at 200 yards, but I'd like to shoot it a little at the local indoor range (20 yards max) so that my first few shots at 200 yards will be on paper.

    I'm aware that the initial crossing of the line of sight is about 25 yards, give or take. I asked the guys at the range if I'd have to hold high/low and how much, and they're still getting the figures for a 20-200 yard conversion (it's a fairly new range). Since I was there, I shot it a bit. Clustered around dead center, so if I was shooting at something 20 yards away, it would be dead on (and VERY DEAD). It would be nice to know when I head over there again where I'd need to have it hitting to at least have it on paper at 200. Thanks in advance, fellas.
     
  2. wired

    wired Guest

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    Okay, I found a chart at the Steyrscout.org that had a rifle zeroed at 233 yards. Info is for a 150-grain, which is probably what I'm gonna be shooting the most of.

    25 yards - 0.1"
    100 yards - 2.9"
    150 yards - 3.1"
    200 yards - 1.8"
    250 yards - -1.2"
    300 yards - -5.9"

    I'm assuming having it hit about 0.5" low at 25 put it pretty close at 200? Granted, the data will vary a bit due to barrel length, etc, etc, but I'm sure it'll get me pretty dang close.
     

  3. wwb

    wwb Super Member

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    Any ballistics calculation will depend on the height of the line of sight above the bore. Unless stated otherwise, it's typically 1.5" (about the height of a scope on standard rings).

    If you're shooting open sights, that distance will be closer to 3/4", and your trajectory will be quite a bit different.

    If I get the time later today, I'll run some figures through my ballistics program.
     
  4. huntswithdogs

    huntswithdogs Moderator

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    Wired,

    When installing a new scope,I get it dead on at 25 yds. For the most part,this gets it on the paper pretty close to center. From the chart that you showed,that should apply here for you also.

    Oh yeah, you were evidently blessed with having good eyes,because I've noticed that you usually talk about not using scopes. Take good care of them and wear your glasses when shooting. Some of us need the aid of the scopes because of old or bad eyes. As myself, I represent both catagories. HAHA


    HWD
     
  5. wired

    wired Guest

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    Well, my eyes ain't as good as you think. At least I'm guaranteed of having something in front of my eyes at all times, because I'm not about to start using contacts. I've gotten used to glasses, and I think I even look better with them on.

    I guess I don't go for scopes so much because I learned how to shoot without them. All those days plinking in the backyard with the air rifle when I was a kid, ya know. The reason I didn't want one on this rifle is because it just feels better without. A scope made it not feel quite so "balanced", for want of a better word. Also, I find it easier to operate the bolt without a scope in the way. If I ever get a rifle specifically for varmint shooting (at longer ranges), I'll probably set that one up with a nice scope.

    Thanks for the info so far, guys. Once I get it at 20-25 yards, I'm going to take the trip out to somewhere I can shoot 200 yards and do the final adjustments. I just don't want to be popping off a whole box of ammo there to try to get it on paper. From what I've seen so far, though, iron sights aren't usually too far off in adjustment, mostly because they have to be in perfect alignment with the barrel to work in the first place. At least the windage is almost perfect most times.
     
  6. wwb

    wwb Super Member

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    This ^%$& work keeps gettin' in the way of fun stuff. I haven't had time to run the numbers 'til now.

    Anyhow, with the sight plane 3/4 inch above the bore centerline, a 150 grain spire point boattal at 2800 fps out of the muzzle gives the following trajectory (at sea level):

    0 yards -0.8
    100 yd +2.3
    200 yd 0.0
    300 yd -8.6
    400 yd -24.7
    500 yd -50.0

    first zero at approx 25 yd