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How far away from the barrel does a scope need to be mounted?

Discussion in 'Rifle Country' started by slowr1der, Sep 20, 2010.

  1. slowr1der

    slowr1der Well-Known Member

    I switched a scope from one gun to another, and ran into a problem. With the only set of rings I have the scope is literally just a hair away from the barrel. If you put a piece of thin computer paper in there, it rubs. You can see light inbetween the barrel and scope, but it's very very close. Is this okay, or do I need higher rings? I've heard the closer the scope is to the barrel the better, but I think I'm too close here. I'm just wondering if after the barrel heats up if it will be touching the scope. Or should I leave it?
  2. Badlander

    Badlander Well-Known Member

    Sounds like it is perfect! let it be.
  3. highorder

    highorder Well-Known Member

  4. JDGray

    JDGray Well-Known Member

    Actually, you need it to be aligned perfectly when you open your eyes after shouldering the rifle with your eyes closed.(Or comfortably against your shoulder prone)
  5. PT1911

    PT1911 Well-Known Member

    Unless you are shooting at long range (for the cartridge) and must compensate for a lot of bullet drop, you want the scope as close to the bore as possible.
  6. JDGray

    JDGray Well-Known Member

    Close to the barrel is desireable, if it fits your face. If you have a very long face, the scope will need to be raised.:D
  7. slowr1der

    slowr1der Well-Known Member

    It's probably .020" at max. So that's enough room? The scope is actually still too high for me to get a great cheek weld, but due to the design I can't get the scope mounted nearly as low as I'd like.
  8. PT1911

    PT1911 Well-Known Member

    How big is the objective? on what sort of gun?
  9. slowr1der

    slowr1der Well-Known Member

    Well, it's a 40mm objective, but it's also an adjustable objective and it makes it very very close with medium rings where a normal 40mm objective would work.
  10. PT1911

    PT1911 Well-Known Member

    if you are clear of the bore (even if really close) that is fine, your only options are to modify your cheek weld or buy an add on cheek riser.
  11. LemmyCaution

    LemmyCaution Well-Known Member

    For most uses, the optics should be as close to the bore line as possible. This is irrespective of cheek weld, which is an entirely separate issue.

    The exception to this rule comes when one is calculating a maximum Point Blank Range.

    Let's compare a somewhat odd example (just because it's what I have loaded in GNU Ballistics right now).

    Assuming an M852 NATO round (168gr OTM in 7.62x51 at 2650fps MV), with the centerline of the optics at 0.5" above the bore line and a vital zone of 10"Ø, the minimum PBR is 0 yards. The maximum PBR is 311 yards.

    If we move the centerline of the optic to 2" above the bore line, the minimum PBR is 0 yards, but the maximum PBR moves to 326 yards.

    OK, now, just because I am curious (and also wanted to explicate one of the reasons the sights on an AR15 are so high above the bore line):

    Assuming an M855 (62gr FMJ in 5.56x45 at 3000fps MV) projectile, with the optical centerline 2.6" above the bore line and a vital zone of 10"Ø, the minimum PBR is 0 yards and the maximum PBR is 349 yards.

    Move the optical centerline to .75" above the bore line and the maximum PBR drops to 332 yards.

    The point is, for typical combat optics, a higher optical centerline gives a longer effective range.
  12. Walkalong

    Walkalong Moderator

  13. Uncle Mike

    Uncle Mike Well-Known Member

    .020" is pretty close, I just set up a rifle that came out to that exact measurement, I would have left it there but the bolt handle was ever so lightly rubbing the ocular bell of the scope, with that thought, you'll transmit a good deal of heat to the objective bell of your scope set with such a small amount of clearance, IF you warm her up at the bench.

    Also, grab the top of your objective bell and the bottom of your rifles forend and squeeze while watching that .020", does it flex enough to touch the barrel, if so your scope is going to take a beating with every shot! This is amplified the further the front scope mounting ring is from the front of the scope.

    IF you don't have a flexing issue, and the bolt handle clears, and you don't plan on any 'heated' range sessions, your good!

    As a rule, which is not cast in stone, we try to leave .100" or so clearance up front to facilitate the use of scope covers and the such, unless the customer specifically wants more or less gap. Also, the greater amount of space allows for seeds, leaves and rain not to accumulate.

    As Lemmy said, cheek weld is another monster you have to sleigh irrespective to you scopes centerline height above the rifles bore centerline, the only way to achieve correct cheek weld is to raise your eye to the scopes centerline, once scope height has been established.

    Some folks like more of a 'heads up' profile with a gaming rifle to allow for the ease of tracking game while in the shooting position, while not looking through the scope, others want a firm 'heads down' benchrest type cheek weld for the same rig.

    While a firm, heads down cheekweld is better for accurate shooting, it really does not pose a great problem if your a tad bit higher than the latter mentioned height for hunting applications, at the ranges you may be shooting game.

    IF you foresee long technical shots on a regular basis while hunting, then a low, firm cheekweld is the way to go.

    If you plan to raise your eye, there are several adjustable and or fixed cheek pieces you can easily install yourself for a nominal cost.




    We use the Accu-Riser brand a lot along with the Karsten, but the Beartooth Comb Raising Kit works just as well and is not expensive, it also does not alter your rifles stock in any way, I have several of the Beartooth units on some of my personal rigs and they work great.

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