Rifle Scopes Ring Height Info - How to Measure Correctly

M

mdmp5

Gunny Sergeant
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    • May 7, 2009
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    #1
    Guys,

    Lately, on average of about 1 per day, I have seen quite a few posts (mostly from newbies) regarding questions about what ring height should be used. They usually request pics for comparison. For all new guys, there is a systematic way of calculating ring height that doesn't require more than a simple elementary school ruler. You measure 3 things:
    1. the height of the front of your base/rail from the barrel
    2. the height of your rings from the top of the rail to centerline
    3. the outside diameter of the bell of the scope (not the size of the objective lens)

    Here is the equation:

    [rail height + ring height] - [bell diameter x 0.5]

    If the value is positive, then your bell will clear the barrel. Ideally, you want that bell to be about 1/4" or less over the barrel. This will give you a tight cheek weld. Be sure to account for Butler Creek caps if you intend on using them.

    If you are using a 40mm objective, then you can use the lowest rings and bases available, as the bell will certainly clear the barrel with no problem. i.e. don't worry if the bell ends up being higher than 1/4" over the barrel.

    Hope this helps.

    mike

    Just another note. If you are using a scope base and/or mount/rings that have built in elevation, that may have to be accounted for in the case of very small clearance. To calculate this, we need to know the amount of elevation built into the mount/rings and/ or base, and the length from the end of the scope base to the end of the scope bell. Convert MOA into degrees, and then the equation is:

    Tan (theta) x length

    For example, if you are using a 20 MOA base, and the distance from the edge of the scope base to the end of the bell is 5". 20 MOA = 0.333 degrees, so:

    Tan 0.333 x 5 = 0.029"

    This means that you need an extra 0.029" of clearance in addition to the calculation above

    -mp
     
    Last edited:
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    #4
    Re: Ring Height Questions

    You also need to take into account the barrel size and the height of the action to the barrel.

    To make it easy,

    40mm or less - low rings all the time
    50mm obj - low rings on < 5 contour
    Medium rings > #5 and up (strait barrel get med high)
    56mm obj Medium on < 5 contour (sometimes med high)
    Medium high on sendero contour
    High on >7 contour

    34mm...
    50mm objective - lows will work all the time
    56mm objective - lows < sendero or #5 contour Sometimes lows will fit number 7 contour barrels, but it depends on how long the shank is after the smith installed it.
    Highs for sure anything larger than #7

    This is assuming our ring height and our rail height. Also using buttler creek caps. YMMV...







     
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    #5
    Re: Ring Height Questions

    Hey Glen...How much more should someone figure in for BC Caps. Ive alwas figured in about another 1/8 of an inch. Whats your thoughts? By the way I love my Seekins Rings...outstanding work and thank you.
     
    #6
    Re: Ring Height Questions

    Great info here. Thanks especially to Glen.

    These are excellent guidelines for use with the more or less "conventional" style of gunstocks, however more and more shooters are using either AR-style platforms and/or Accuracy International rifles or the AICS chassis both of which are a whole different ball of wax!

    Most AR shooters need an Ultra-High ring (approx. 1.4" ring height), while High rings (approx. 1.125" ring height) seem to work the best for AI-style shooters, both regardless of objective diameter. The old adage of "mount your scope as low as possible" just doesn't work for most folks with these new stock designs.

    Of course YMMV
    smile.gif
     
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    #7
    Re: Ring Height Questions

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bdh308</div><div class="ubbcode-body">You may want to change the title of this post to something like "Make a Sticky: Measuring Ring Height" because it just looks like another ring height question.</div></div>

    Good idea; I will do that
     
    #8
    Re: Ring Height Questions

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: heatseekins</div><div class="ubbcode-body">You also need to take into account the barrel size and the height of the action to the barrel.

    To make it easy,

    40mm or less - low rings all the time
    50mm obj - low rings on < 5 contour
    Medium rings > #5 and up (strait barrel get med high)
    56mm obj Medium on < 5 contour (sometimes med high)
    Medium high on sendero contour
    High on >7 contour

    34mm...
    50mm objective - lows will work all the time
    56mm objective - lows < sendero or #5 contour Sometimes lows will fit number 7 contour barrels, but it depends on how long the shank is after the smith installed it.
    Highs for sure anything larger than #7

    This is assuming our ring height and our rail height. Also using buttler creek caps. YMMV...

    </div></div>

    Thanks for the addt'l info Glen
     
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    #9
    Re: Ring Height Questions

    The above is taking into account the butler creek caps. The ones i have are aprox .035-.040 thick and get thinner when stretched over the scope. I have been known to sand down butler creek caps to allow the use of lowest possible rings...

    Clearance is just that, it doesn't matter if you have 1/16 inch or a foot, its still clearance. On a .50 cal it might matter...
     
    #11
    Re: Ring Height Questions

    I have no problems with bell/barrel clearance - but as we speak am having a mounting issue where the scope's bell is making contact with the forward end of the 20MOA base(a Seekins base as it happens). I can't get the scope back quite far enough for proper relief without contact with low or medium rings on my 700P. (Scope is 10x40 SS)

     
    #12
    Re: Ring Height Questions

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Fritz24</div><div class="ubbcode-body">I have no problems with bell/barrel clearance - but as we speak am having a mounting issue where the scope's bell is making contact with the forward end of the 20MOA base(a Seekins base as it happens). I can't get the scope back far enough for proper relief without contact with low or medium rings on my 700P. (Scope is 10x40 SS)

    Is it just me? </div></div>

    I personally havent heard of this problem. It may come down to you needing a different mount. Maybe Glen or someone will chime in with a solution.
     
    #13
    Re: Ring Height Questions

    I quoted myself from one of the almost daily newb inquiries I had the energy to answer recently:

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">Get a handful of change and stack change under scope on both sides of erector housing until its the height you want, then measure the change stack and add 1/2 the diameter of the tube. </div></div>
     
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    #17
    Re: Ring Height Questions

    Well, there is always going to be some kind of exception. Like USO's short 10 power scope. it will hit the front of the rail like you describe.

    If it is hitting the front then you have 2 options.
    1 higher rings
    2 cut the front of the base back

    AR's are completely different. I prefer 1.4" for mine. That is from the top of a normal M4 rail. i also prefer my scope way forward so i get close to the charging handle.
    We are working on a kick butt rail riser AND a set of 1.4" tall rings that are all one piece. 30 and 34mm with MOA built in. Not going to happen for just a bit, probably going to be a mad dash build for shot show so you wont see them until sometime next year.
     
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    #18
    Re: Ring Height Questions

    Isnt there enough elevation in the SS that he wouldnt have to use a canted rail anyway? He could just mount standard mounts. I guess the question is how far is he shooting?
     
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    #27
    Re: Ring Height Info - How to Measure Correctly

    lol, here i thought i was being original. i bought my rifle then base and then my scope. i wanted the scope as low and close to the barrel as possible. i stacked pennies on the rail and measured them. didnt add any to that, but since Burris listed the heights of their rings it was easy to get the right ones. the low ones were 1/4" and that was perfect. i wish all rings listed their heights
     
    #31
    Re: Ring Height Info - How to Measure Correctly

    The above equation does not account for the slope of the rail, which can make a difference, especially with a 45 MOA rail and a long scope.

    If you have the scope and the rail in hand, an easy check is to calculate the distance between the rail and the tube for the rings you are considering, then find objects of that height and use them as spacers to verify the fit. I use hex nuts or bar stock wrapped in tape. This is also handy for checking if there will be interference with various rail mounted accessories.

     
    #32
    Re: Ring Height Info - How to Measure Correctly

    Mathematically, the differences in clearance are small between angled bases, but may make a difference if you are super close to the barrel. 10 MOA = 1/6 degrees, which is 10.47" @ 100 yds; at 1 yd, it is 0.1047", and at 1 inch, it is 0.0029". Using a 20 MOA base, if your scope with a sun shade extends 10" past the front of the rail, you are looking at 0.058" (1.5mm) difference in height from the front of the rail to the front of the bell. For a 45 MOA base, this would equate to 0.13" (3.3mm). This, of course, is comparing an angled base to a 0 MOA base.

    From the Seekins website:

    For every 10 MOA over the standard 20 MOA base, you subtract 0.01" from the height of the base.
     
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    #33
    Re: Ring Height Info - How to Measure Correctly

    Its fine for a quick calculation for a basic setup. However, sometimes you're better off having the scope in front of you and checking the fit with some improvised spacers before selecting the rings.

    Spacer height = ring height - (tube dia. / 2)
    1mm = 0.039"

    Find something just under and built it up with tape (also protects the finish).

    Things you might want to check:
    -Can you see over your suppressor?
    -Can you see accessories (level, ACI,...) or are they obscured by things like the parallax knob? PH have BIG knobs...
    -Is there interference between any parts of the scope and the rail?
    -Is there any interference between rail mounted accessories (level, ACI,...) and parts of the scope other than the tube?
    -If you have a folding level, is there interference when you fold it?
    -Do you have enough space for switching barrels if your rifle is capable? The Sako Quad requires you to tilt the barrel up before you can pull it out...
    -Can you still install your mirage sheild, sunshade or other things that aren't always on?

    Rings can be expensive and many places won't let you return them once they've been mounted. Doing a quick mock-up may take a bit longer in term of ordering parts, but it can save you some headaches.
     
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    #34
    Re: Ring Height Questions

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: heatseekins</div><div class="ubbcode-body">You also need to take into account the barrel size and the height of the action to the barrel.

    To make it easy,

    40mm or less - low rings all the time
    50mm obj - low rings on < 5 contour
    Medium rings > #5 and up (strait barrel get med high)
    56mm obj Medium on < 5 contour (sometimes med high)
    Medium high on sendero contour
    High on >7 contour

    34mm...
    50mm objective - lows will work all the time
    56mm objective - lows < sendero or #5 contour Sometimes lows will fit number 7 contour barrels, but it depends on how long the shank is after the smith installed it.
    Highs for sure anything larger than #7

    This is assuming our ring height and our rail height. Also using buttler creek caps. YMMV...
    </div></div>
    Glen, what brand barrel do you reference your contour #'s from?
     
    #35
    Re: Ring Height Info - How to Measure Correctly

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: palmik</div><div class="ubbcode-body">Guys,
    If you are using a 40mm objective, then you can use the lowest rings and bases available, as the bell will certainly clear the barrel with no problem. i.e. don't worry if the bell ends up being higher than 1/4" over the barrel. mike </div></div>

    There is one exception to his rule. If you are mounting a scope on an H&R Handi-Rifle you will need at least medium if not high rings for a 40mm objective. The problem is clearance between the eyepiece end of the scope and the exposed hammer. I know from having two of these rifles in .223 and one in .308.
     
    #36
    Re: Ring Height Info - How to Measure Correctly

    The Brownells video:
    http://www.wonderhowto.com/how-to/video/...le-267112/view/

    The Midway video:
    http://www.youtube.com/watch?v=gpLi064e_JI

    scopesch.jpg


    Dimension B can vary from manufacturer to manufacturer.
    High could be .534" with Badger and 3/4" for Burris extreme tactical 30mm.

    My solution is to stock a file folder box full of rings, with the 1" segregated from the 30mm rings.

    http://swfa.com/Mounts-Rings-and-Bases-C573.aspx

    What does it all mean?
    As in plumbing, buy 'em all.
     
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    #38
    Re: Ring Height Info - How to Measure Correctly

    What if you have neither the scope nor the rings to measure. IOW - you are ordering both the scope and the rings online and you want them there at the same time - how do you know which rings to get for which scope for your gun and base?
     
    #39
    Re: Ring Height Info - How to Measure Correctly

    Get the measurements from the mfrs and plug in the numbers. Make sure your stock doesn't extend very high like a Sako TRG.
     
    #41
    Re: Ring Height Info - How to Measure Correctly

    The problem is that some folks want to order the rings and bases all in one pass so formulas can't do much for you in that instance. I've got a 3.5-15x50 NXS I'm wanting to mount on a stock 5R 308 using a Badger 20 MOA base and Badger rings. I plan to order the base and rings at the same time and use Butler Creek caps...

    What size rings do I use? 0.885 Badgers?

    -David
    Edgewood, NM
     
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    #45
    Re: Ring Height Info - How to Measure Correctly

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: kombayotch</div><div class="ubbcode-body">Its fine for a quick calculation for a basic setup. However, sometimes you're better off having the scope in front of you and checking the fit with some improvised spacers before selecting the rings.

    -Is there interference between any parts of the scope and the rail?
    </div></div>

    This is one I've run into a few times. A Falcon or USO ocular can hit the rear of your scope base when using low rings even if there is plenty of clearance between the bell housing and the barrel. It all depends on your LoP and the eye relief of the scope and possibly if you have an extended scope base. If you're trying to get as low as possible it's going to come down to individual situations, a chart isn't going to tell you.
     
    #46
    Re: Ring Height Info - How to Measure Correctly

    As another newbie I can say thank you for this post. It saves me from embarrassing myself asking this question again.

    I also agree I wish all manufacturers listed the height of their rings. For example I am looking at the LaRue "ultra-low" rings. From the pictures on their website it looks like it will clear a Leupold MK4 40mm in a 20MOA base mounted on a Remmy LTR...but without knowing the measurements who know what else it will work with.

    I think a lot of the problems newbies like myself have is without the specific equipment in hand to measure, and with many manufacturers not being forthcoming with the information it is hard to apply the formulas here.
     
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