56 MM Objective Question

Discussion in 'Long Range Scopes and Other Optics' started by Grey Eagle, May 6, 2015.

  1. Grey Eagle

    Grey Eagle Member

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    I assume with that large of an objective, the highest rings are the only ones that will allow the objective bell to clear the barrel?
     
  2. Senderofan

    Senderofan Well-Known Member

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    No...Not necessarily. It depends on other variables like barrel contour, height of scope base(s) and perhaps even the true outside diameter of the front objective ( some have very thick material around the front objective lens) as well.

    All of my 56mm front objective scopes have 1" rings. I did have to use 1.25" rings for a scope with a 60mm front objective.

    [​IMG]56mm front objective...NightForce 20 moa extended one piece base with Badger Mx 50 1.0" ( Their "High" rings ) with a heavy contour...almost MTU barrel. On a Remington action.

    [​IMG] This is another scope...same kind as above...with the same Badger rings....but on this rifle...I have a Ken Farrell 20 moa one piece base. This rifle has a very similar contoured barrel as the above rifle but there is even more space between the objective and barrel. So, the thickness of the base is one variable coming into play.

    [​IMG] This scope has a 56mm front objective but the material around it is thinner. This is on a Remington action with 1" high Seekins rings and a one piece 20 moa NightForce base. The rifle barrel is a heavy Palma contour. It is the slimmest barrel I have and consequently this rifle has the largest gap between the front objective and the barrel.

    [​IMG] Last picture...a third brand of scope with a 56mm front objective, Ken Farrell one piece 20 moa base and 1" Farrell rings on a rifle with a Krieger MTU contoured barrel. Probably has the least amount of space between the objective and barrel.

    So...there are variables other than just the front objective....that need to be taken into account when buying the correct rings. I've gone with all 1" high for mine....so I can swap scopes from rifle to rifle, if need be, and I know there won't be an issue. Even if I swap to a straight cylinder barrel.....I should have clearance.

    Here's a handy little calculator that might be of help: http://www.mil-rad.com/scope_ring_calculator

    Wayne
     
  3. Grey Eagle

    Grey Eagle Member

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    Thanks Senderofan! It will be going on a Thompson/Center Encore 280AI, so there will be no step between the barrel and the action, like on a bolt action. I guess I might need extra high.
     
  4. Senderofan

    Senderofan Well-Known Member

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    That will depend on what scope base you go with....IMHO. If you can get the thickness of that.....it might help you calculate what ring height you need without going too high. There is a fair amount of variability with talking about the "Highest rings". This is a list of NightForce ring heights, I picked them since they have a nice list with different options in the "High" category:


    Height:
    Low: 0.885"
    Medium: 1.00"
    High: 1.125"
    Intermediate High: 1.265"
    Extra High: 1.375"
    Extreme High: 1.50"



    So, if you have the scope and can measure the outside of the front objective..... I've seen a fair amount say an average 56mm measures 60mm on the outside. You are working with half of that....anything above 30mm will get you space above the barrel. The NightForce "High" rings..1.125" will get you 28.575mm above the scope base.... ( 1.125" x 25.4mm ( which is an inch in mm's)) My Farrell bases add at least 1/4" to the height of my scope...or 6.35mm. So in that scenario...add it all up and you'd have 5mm of space by itself............. or 3mm's ( about 1/8th of an inch) with a Butler Creek front cover on the front of that scope( Butler Creeks add 2mm around the front objective.) If you didn't take the time to measure and calculate....and got the 1.5" rings....you'd probably have a ton of space and might have issues with site picture unless you build up the cheekpiece.

    Of course the Intermediate High rings would probably give you space to spare and not have to think about how thick your base is.

    Just some ramblings from an old fart varmint hunter.

    Best of Luck,

    Wayne

    If you go with a canted base(s).....you might lose a little height of the base due to the scope being tilted towards the barrel.
     
  5. WapitiBob

    WapitiBob Well-Known Member

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    Oct 16, 2011
    I have an NXS 56MM on NF 20moa rail and Low NF rings, on a brux #5.

    Plenty of room.
     
  6. Grey Eagle

    Grey Eagle Member

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    Thanks Wayne! After I posted, I remembered I have the Picatinny rail installed. I will measure the height of that. I don't have the scope yet. I am looking at an IOR 4.5-14x56. Maybe I can find the outside diameter of the bell online.